<?xml version='1.0'encoding='utf-8'?> <?xml-stylesheet type="text/xsl" href="rfc2629.xslt" ?> <!-- generated by https://github.com/cabo/kramdown-rfc2629 version 1.3.24 -->encoding='UTF-8'?> <!DOCTYPE rfcSYSTEM "rfc2629-xhtml.ent"> <?rfc toc="yes"?> <?rfc sortrefs="yes"?> <?rfc symrefs="yes"?> <?rfc docmapping="yes"?>[ <!ENTITY nbsp " "> <!ENTITY zwsp "​"> <!ENTITY nbhy "‑"> <!ENTITY wj "⁠"> ]> <rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-quic-http-34"category="std"number="9114" obsoletes="" updates="" submissionType="IETF" category="std" consensus="true" xml:lang="en" tocInclude="true" sortRefs="true" symRefs="true" version="3"><!-- xml2rfc v2v3 conversion 3.5.0 --><link href='https://datatracker.ietf.org/doc/draft-ietf-quic-http-latest' rel='prev'/> <front><title abbrev="HTTP/3">Hypertext Transfer Protocol Version 3 (HTTP/3)</title><title>HTTP/3</title> <seriesInfoname="Internet-Draft" value="draft-ietf-quic-http-34"/>name='RFC' value='9114'/> <authorinitials="M." surname="Bishop" fullname="Mike Bishop" role="editor">fullname='Mike Bishop' initials='M.' role='editor' surname='Bishop'> <organization>Akamai</organization> <address> <email>mbishop@evequefou.be</email> </address> </author> <dateyear="2021" month="February" day="02"/>month='June' year='2022'/> <area>Transport</area> <workgroup>QUIC</workgroup> <keyword>HTTP/2</keyword> <keyword>HPACK</keyword> <keyword>QPACK</keyword> <keyword>Web</keyword> <abstract> <t>The QUIC transport protocol has several features that are desirable in a transport for HTTP, such as stream multiplexing, per-stream flow control, and low-latency connection establishment. This document describes a mapping of HTTP semantics over QUIC. This document also identifies HTTP/2 features that are subsumed byQUIC,QUIC and describes how HTTP/2 extensions can be ported to HTTP/3.</t> </abstract><note> <name>DO NOT DEPLOY THIS VERSION OF HTTP</name> <t>DO NOT DEPLOY THIS VERSION OF HTTP/3 UNTIL IT IS IN AN RFC. This version is still a work in progress. For trial deployments, please use earlier versions.</t> </note> <note> <name>Note to Readers</name> <t>Discussion of this draft takes place on the QUIC working group mailing list (quic@ietf.org), which is archived at <eref target="https://mailarchive.ietf.org/arch/search/?email_list=quic"/>.</t> <t>Working Group information can be found at <eref target="https://github.com/quicwg"/>; source code and issues list for this draft can be found at <eref target="https://github.com/quicwg/base-drafts/labels/-http"/>.</t> </note></front> <middle> <sectionanchor="introduction" numbered="true" toc="default">anchor='introduction'> <name>Introduction</name> <t>HTTP semantics (<xreftarget="SEMANTICS" format="default"/>)target='RFC9110'/>) are used for a broad range of services on the Internet. These semantics have most commonly been used with HTTP/1.1 and HTTP/2. HTTP/1.1 has been used over a variety of transport and session layers, while HTTP/2 has been used primarily with TLS over TCP. HTTP/3 supports the same semantics over a new transportprotocol,protocol: QUIC.</t> <sectionanchor="prior-versions-of-http" numbered="true" toc="default">anchor='prior-versions-of-http'> <name>PriorversionsVersions of HTTP</name> <t>HTTP/1.1 (<xreftarget="HTTP11" format="default"/>)target='RFC9112'/>) uses whitespace-delimited text fields to convey HTTP messages. While these exchanges arehuman-readable,human readable, using whitespace for message formatting leads to parsing complexity and excessive tolerance of variant behavior.</t> <t>Because HTTP/1.1 does not include a multiplexing layer, multiple TCP connections are often used to service requests in parallel. However, that has a negative impact on congestion control and network efficiency, since TCP does not share congestion control across multiple connections.</t> <t>HTTP/2 (<xreftarget="HTTP2" format="default"/>)target='RFC9113'/>) introduced a binary framing and multiplexing layer to improve latency without modifying the transport layer. However, because the parallel nature of HTTP/2's multiplexing is not visible to TCP's loss recovery mechanisms, a lost or reordered packet causes all active transactions to experience a stall regardless of whether that transaction was directly impacted by the lost packet.</t> </section> <sectionanchor="delegation-to-quic" numbered="true" toc="default">anchor='delegation-to-quic'> <name>Delegation to QUIC</name> <t>The QUIC transport protocol incorporates stream multiplexing and per-stream flow control, similar to that provided by the HTTP/2 framing layer. By providing reliability at the stream level and congestion control across the entire connection, QUIC has the capability to improve the performance of HTTP compared to a TCP mapping. QUIC also incorporates TLS 1.3 (<xreftarget="TLS13" format="default"/>)target='TLS'/>) at the transport layer, offering comparable confidentiality and integrity to running TLS over TCP, with the improved connection setup latency of TCP Fast Open (<xreftarget="TFO" format="default"/>).</t>target='TFO'/>).</t> <t>This document definesHTTP/3,HTTP/3: a mapping of HTTP semantics over the QUIC transport protocol, drawing heavily on the design of HTTP/2. HTTP/3 relies on QUIC to provide confidentiality and integrity protection of data; peer authentication; and reliable, in-order, per-stream delivery. While delegating stream lifetime andflow controlflow-control issues to QUIC, a binary framing similar to the HTTP/2 framing is used on each stream. Some HTTP/2 features are subsumed by QUIC, while other features are implemented atop QUIC.</t> <t>QUIC is described in <xreftarget="QUIC-TRANSPORT" format="default"/>.target='QUIC-TRANSPORT'/>. For a full description of HTTP/2, see <xreftarget="HTTP2" format="default"/>.</t>target='RFC9113'/>.</t> </section> </section> <sectionanchor="http3-protocol-overview" numbered="true" toc="default">anchor='http3-protocol-overview'> <name>HTTP/3 Protocol Overview</name> <t>HTTP/3 provides a transport for HTTP semantics using the QUIC transport protocol and an internal framing layer similar to HTTP/2.</t> <t>Once a client knows that an HTTP/3 server exists at a certain endpoint, it opens a QUIC connection. QUIC provides protocol negotiation, stream-based multiplexing, and flow control. Discovery of an HTTP/3 endpoint is described in <xreftarget="discovery" format="default"/>.</t>target='discovery'/>.</t> <t>Within each stream, the basic unit of HTTP/3 communication is a frame (<xreftarget="frames" format="default"/>).target='frames'/>). Each frame type serves a different purpose. For example,HEADERS<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> andDATA<xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frames form the basis of HTTP requests and responses (<xreftarget="request-response" format="default"/>).target='request-response'/>). Frames that apply to the entire connection are conveyed on a dedicatedcontrol stream.</t><xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>.</t> <t>Multiplexing of requests is performed using the QUIC stream abstraction, which is described in <xrefsection="2" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>.section='2' sectionFormat='of' target='QUIC-TRANSPORT'/>. Each request-response pair consumes a single QUIC stream. Streams are independent of each other, so one stream that is blocked or suffers packet loss does not prevent progress on other streams.</t> <t>Server push is an interaction mode introduced in HTTP/2 (<xreftarget="HTTP2" format="default"/>)target='RFC9113'/>) that permits a server to push a request-response exchange to a client in anticipation of the client making the indicated request. This trades off network usage against a potential latency gain. Several HTTP/3 frames are used to manage server push, such asPUSH_PROMISE, MAX_PUSH_ID,<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/>, <xref format='none' target='frame-max-push-id'>MAX_PUSH_ID</xref><iref item='MAX_PUSH_ID'/>, andCANCEL_PUSH.</t><xref format='none' target='frame-cancel-push'>CANCEL_PUSH</xref><iref item='CANCEL_PUSH'/>.</t> <t>As in HTTP/2, request and response fields are compressed for transmission. Because HPACK (<xreftarget="HPACK" format="default"/>)target='HPACK'/>) relies on in-order transmission of compressed field sections (a guarantee not provided by QUIC), HTTP/3 replaces HPACK with QPACK (<xreftarget="QPACK" format="default"/>).target='RFC9204'/>). QPACK uses separate unidirectional streams to modify and track field table state, while encoded field sections refer to the state of the table without modifying it.</t> <sectionanchor="document-organization" numbered="true" toc="default">anchor='document-organization'> <name>Document Organization</name> <t>The following sections provide a detailed overview of the lifecycle of an HTTP/3 connection:</t> <ulspacing="normal"> <li>Connection Setup and Managementspacing='normal'> <li>"<xref format='title' target='connection-setup'/>" (<xreftarget="connection-setup" format="default"/>)target='connection-setup'/>) covers how an HTTP/3 endpoint is discovered and an HTTP/3 connection is established.</li><li>HTTP Request Lifecycle<li>"<xref format='title' target='http-request-lifecycle'/>" (<xreftarget="http-request-lifecycle" format="default"/>)target='http-request-lifecycle'/>) describes how HTTP semantics are expressed using frames.</li><li>Connection Closure<li>"<xref format='title' target='connection-closure'/>" (<xreftarget="connection-closure" format="default"/>)target='connection-closure'/>) describes how HTTP/3 connections are terminated, either gracefully or abruptly.</li> </ul> <t>The details of the wire protocol and interactions with the transport are described in subsequent sections:</t> <ulspacing="normal"> <li>Stream Mapping and Usagespacing='normal'> <li>"<xref format='title' target='stream-mapping'/>" (<xreftarget="stream-mapping" format="default"/>)target='stream-mapping'/>) describes the way QUIC streams are used.</li><li>HTTP Framing Layer<li>"<xref format='title' target='http-framing-layer'/>" (<xreftarget="http-framing-layer" format="default"/>)target='http-framing-layer'/>) describes the frames used on most streams.</li><li>Error Handling<li>"<xref format='title' target='errors'/>" (<xreftarget="errors" format="default"/>)target='errors'/>) describes how error conditions are handled and expressed, either on a particular stream or for the connection as a whole.</li> </ul> <t>Additional resources are provided in the final sections:</t> <ulspacing="normal"> <li>Extensions to HTTP/3spacing='normal'> <li>"<xref format='title' target='extensions'/>" (<xreftarget="extensions" format="default"/>)target='extensions'/>) describes how new capabilities can be added in future documents.</li> <li>A more detailed comparison between HTTP/2 and HTTP/3 can be found in <xreftarget="h2-considerations" format="default"/>.</li>target='h2-considerations'/>.</li> </ul> </section> <sectionanchor="conventions-and-terminology" numbered="true" toc="default">anchor='conventions-and-terminology'> <name>Conventions and Terminology</name> <t>The key words"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY","<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>", "<bcp14>MAY</bcp14>", and"OPTIONAL""<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as described in BCP 14 <xref target="RFC2119" format="default"/> <xref target="RFC8174" format="default"/> when, and only when, they appear in all capitals, as shown here.</t> <t>This document uses the variable-length integer encoding from <xreftarget="QUIC-TRANSPORT" format="default"/>.</t>target='QUIC-TRANSPORT'/>.</t> <t>The following terms are used:</t> <dl><dt> abort: </dt><dt>abort:</dt> <dd> <t>An abrupt termination of a connection or stream, possibly due to an error condition.</t> </dd><dt> client: </dt><dt>client:</dt> <dd> <t>The endpoint that initiates an HTTP/3 connection. Clients send HTTP requests and receive HTTP responses.</t> </dd><dt> connection: </dt><dt>connection:</dt> <dd> <t>A transport-layer connection between twoendpoints,endpoints using QUIC as the transport protocol.</t> </dd><dt> connection error: </dt><dt><xref format='none' target='errors'>connection error</xref><iref item='connection error'/>:</dt> <dd> <t>An error that affects the entire HTTP/3 connection.</t> </dd><dt> endpoint: </dt><dt>endpoint:</dt> <dd> <t>Either the client or server of the connection.</t> </dd><dt> frame: </dt><dt>frame:</dt> <dd> <t>The smallest unit of communication on a stream in HTTP/3, consisting of a header and a variable-length sequence of bytes structured according to the frametype. </t>type.</t> <t>Protocol elements called "frames" exist in both this document and <xreftarget="QUIC-TRANSPORT" format="default"/>.target='QUIC-TRANSPORT'/>. Where frames from <xreftarget="QUIC-TRANSPORT" format="default"/>target='QUIC-TRANSPORT'/> are referenced, the frame name will be prefaced with"QUIC.""QUIC". For example, "QUIC CONNECTION_CLOSEframes."frames". References without this preface refer to frames defined in <xreftarget="frames" format="default"/>.</t>target='frames'/>.</t> </dd><dt> HTTP/3 connection: </dt><dt>HTTP/3 connection:</dt> <dd> <t>A QUIC connection where the negotiated application protocol is HTTP/3.</t> </dd><dt> peer: </dt><dt>peer:</dt> <dd> <t>An endpoint. When discussing a particular endpoint, "peer" refers to the endpoint that is remote to the primary subject of discussion.</t> </dd><dt> receiver: </dt><dt>receiver:</dt> <dd> <t>An endpoint that is receiving frames.</t> </dd><dt> sender: </dt><dt>sender:</dt> <dd> <t>An endpoint that is transmitting frames.</t> </dd><dt> server: </dt><dt>server:</dt> <dd> <t>The endpoint that accepts an HTTP/3 connection. Servers receive HTTP requests and send HTTP responses.</t> </dd><dt> stream: </dt><dt>stream:</dt> <dd> <t>A bidirectional or unidirectional bytestream provided by the QUIC transport. All streams within an HTTP/3 connection can be considered "HTTP/3streams,"streams", but multiple stream types are defined within HTTP/3.</t> </dd><dt> stream error: </dt><dt><xref format='none' target='errors'>stream error</xref><iref item='stream error'/>:</dt> <dd> <t>An application-level error on the individual stream.</t> </dd> </dl> <t>The term "content" is defined in <xrefsection="6.4" sectionFormat="of" target="SEMANTICS" format="default"/>.</t>section='6.4' sectionFormat='of' target='RFC9110'/>.</t> <t>Finally, the terms "resource", "message", "user agent", "origin server", "gateway", "intermediary", "proxy", and "tunnel" are defined in <xrefsection="3" sectionFormat="of" target="SEMANTICS" format="default"/>.</t>section='3' sectionFormat='of' target='RFC9110'/>.</t> <t>Packet diagrams in this document use the format defined in <xrefsection="1.3" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>section='1.3' sectionFormat='of' target='QUIC-TRANSPORT'/> to illustrate the order and size of fields.</t> </section> </section> <sectionanchor="connection-setup" numbered="true" toc="default">anchor='connection-setup'> <name>Connection Setup and Management</name> <sectionanchor="discovery" numbered="true" toc="default">anchor='discovery'> <name>Discovering an HTTP/3 Endpoint</name> <t>HTTP relies on the notion of an authoritative response: a response that has been determined to be the most appropriate response for that request given the state of the target resource at the time of response message origination by (or at the direction of) the origin server identified within the target URI. Locating an authoritative server for an HTTP URI is discussed in <xrefsection="4.3" sectionFormat="of" target="SEMANTICS" format="default"/>.</t>section='4.3' sectionFormat='of' target='RFC9110'/>.</t> <t>The "https" scheme associates authority with possession of a certificate that the client considers to be trustworthy for the host identified by the authority component of the URI. Upon receiving a server certificate in the TLS handshake, the clientMUST<bcp14>MUST</bcp14> verify that the certificate is an acceptable match for the URI's origin server using the process described in <xrefsection="4.3.4" sectionFormat="of" target="SEMANTICS" format="default"/>.section='4.3.4' sectionFormat='of' target='RFC9110'/>. If the certificate cannot be verified with respect to the URI's origin server, the clientMUST NOT<bcp14>MUST NOT</bcp14> consider the server authoritative for that origin.</t> <t>A clientMAY<bcp14>MAY</bcp14> attempt access to a resource with an "https" URI by resolving the host identifier to an IP address, establishing a QUIC connection to that address on the indicated port (including validation of the server certificate as described above), and sending an HTTP/3 request message targeting the URI to the server over that secured connection. Unless some other mechanism is used to select HTTP/3, the token "h3" is used in theApplication LayerApplication-Layer Protocol Negotiation (ALPN; see <xreftarget="RFC7301" format="default"/>)target='RFC7301'/>) extension during the TLS handshake.</t> <t>Connectivity problems (e.g., blocking UDP) can result in a failure to establish a QUICconnection establishment failure;connection; clientsSHOULD<bcp14>SHOULD</bcp14> attempt to use TCP-based versions of HTTP in this case.</t> <t>ServersMAY<bcp14>MAY</bcp14> serve HTTP/3 on any UDP port; an alternative service advertisement always includes an explicit port, and URIs contain either an explicit port or a default port associated with the scheme.</t> <sectionanchor="alt-svc" numbered="true" toc="default">anchor='alt-svc'> <name>HTTP Alternative Services</name> <t>An HTTP origin can advertise the availability of an equivalent HTTP/3 endpoint via the Alt-Svc HTTP response header field or the HTTP/2 ALTSVC frame (<xreftarget="ALTSVC" format="default"/>),target='ALTSVC'/>) using the "h3" ALPN token.</t> <t>For example, an origin could indicate in an HTTP response that HTTP/3 was available on UDP port 50781 at the same hostname by including the following header field:</t><artwork type="example" name="" align="left" alt=""><![CDATA[<sourcecode type='http-message'><![CDATA[ Alt-Svc: h3=":50781"]]></artwork>]]></sourcecode> <t>On receipt of an Alt-Svc record indicating HTTP/3 support, a clientMAY<bcp14>MAY</bcp14> attempt to establish a QUIC connection to the indicated host and port; if this connection is successful, the client can send HTTP requests using the mapping described in this document.</t> </section> <sectionanchor="other-schemes" numbered="true" toc="default">anchor='other-schemes'> <name>Other Schemes</name> <t>Although HTTP is independent of the transport protocol, the "http" scheme associates authority with the ability to receive TCP connections on the indicated port of whatever host is identified within the authority component. Because HTTP/3 does not use TCP, HTTP/3 cannot be used for direct access to the authoritative server for a resource identified by an "http" URI. However, protocol extensions such as <xreftarget="ALTSVC" format="default"/>target='ALTSVC'/> permit the authoritative server to identify other services that are also authoritative and that might be reachable over HTTP/3.</t> <t>Prior to making requests for an origin whose scheme is not "https", the clientMUST<bcp14>MUST</bcp14> ensure the server is willing to serve that scheme. For origins whose scheme is "http", an experimental method to accomplish this is described in <xreftarget="RFC8164" format="default"/>.target='RFC8164'/>. Other mechanisms might be defined for various schemes in the future.</t> </section> </section> <sectionanchor="connection-establishment" numbered="true" toc="default">anchor='connection-establishment'> <name>Connection Establishment</name> <t>HTTP/3 relies on QUIC version 1 as the underlying transport. The use of other QUIC transport versions with HTTP/3MAY<bcp14>MAY</bcp14> be defined by future specifications.</t> <t>QUIC version 1 uses TLS version 1.3 or greater as its handshake protocol. HTTP/3 clientsMUST<bcp14>MUST</bcp14> support a mechanism to indicate the target host to the server during the TLS handshake. If the server is identified by a domain name (<xreftarget="DNS-TERMS" format="default"/>),target='DNS-TERMS'/>), clientsMUST<bcp14>MUST</bcp14> send the Server Name Indication (SNI; <xreftarget="RFC6066" format="default"/>)target='RFC6066'/>) TLS extension unless an alternative mechanism to indicate the target host is used.</t> <t>QUIC connections are established as described in <xreftarget="QUIC-TRANSPORT" format="default"/>.target='QUIC-TRANSPORT'/>. During connection establishment, HTTP/3 support is indicated by selecting the ALPN token "h3" in the TLS handshake. Support for other application-layer protocolsMAY<bcp14>MAY</bcp14> be offered in the same handshake.</t> <t>While connection-level options pertaining to the core QUIC protocol are set in the initial crypto handshake,HTTP/3-specificsettings specific to HTTP/3 are conveyed in theSETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame. After the QUIC connection is established, aSETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame(<xref target="frame-settings" format="default"/>) MUST<bcp14>MUST</bcp14> be sent by each endpoint as the initial frame of their respective HTTPcontrol stream; see<xreftarget="control-streams" format="default"/>.</t>format='none' target='control-streams'>control stream</xref><iref item='control stream'/>.</t> </section> <sectionanchor="connection-reuse" numbered="true" toc="default">anchor='connection-reuse'> <name>Connection Reuse</name> <t>HTTP/3 connections are persistent across multiple requests. For best performance, it is expected that clients will not close connections until it is determined that no further communication with a server is necessary (for example, when a user navigates away from a particular web page) or until the server closes the connection.</t> <t>Once a connectionexiststo a serverendpoint,endpoint exists, this connectionMAY<bcp14>MAY</bcp14> be reused for requests with multiple different URI authority components. To use an existing connection for a new origin, clientsMUST<bcp14>MUST</bcp14> validate the certificate presented by the server for the new origin server using the process described in <xrefsection="4.3.4" sectionFormat="of" target="SEMANTICS" format="default"/>.section='4.3.4' sectionFormat='of' target='RFC9110'/>. This implies that clients will need to retain the server certificate and any additional information needed to verify that certificate; clientswhichthat do not do so will be unable to reuse the connection for additional origins.</t> <t>If the certificate is not acceptable with regard to the new origin for any reason, the connectionMUST NOT<bcp14>MUST NOT</bcp14> be reused and a new connectionSHOULD<bcp14>SHOULD</bcp14> be established for the new origin. If the reason the certificate cannot be verified might apply to other origins already associated with the connection, the clientSHOULD re-validate<bcp14>SHOULD</bcp14> revalidate the server certificate for those origins. For instance, if validation of a certificate fails because the certificate has expired or been revoked, this might be used to invalidate all other origins for which that certificate was used to establish authority.</t> <t>ClientsSHOULD NOT<bcp14>SHOULD NOT</bcp14> open more than one HTTP/3 connection to a given IP address and UDP port, where the IP address and port might be derived from a URI, a selected alternative service (<xreftarget="ALTSVC" format="default"/>),target='ALTSVC'/>), a configured proxy, or name resolution of any of these. A clientMAY<bcp14>MAY</bcp14> open multiple HTTP/3 connections to the same IP address and UDP port using different transport or TLS configurations butSHOULD<bcp14>SHOULD</bcp14> avoid creating multiple connections with the same configuration.</t> <t>Servers are encouraged to maintain open HTTP/3 connections for as long as possible but are permitted to terminate idle connections if necessary. When either endpoint chooses to close the HTTP/3 connection, the terminating endpointSHOULD<bcp14>SHOULD</bcp14> first send aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame (<xreftarget="connection-shutdown" format="default"/>)target='connection-shutdown'/>) so that both endpoints can reliably determine whether previously sent frames have been processed and gracefully complete or terminate any necessary remaining tasks.</t> <t>A server that does not wish clients to reuse HTTP/3 connections for a particular origin can indicate that it is not authoritative for a request by sending a 421 (Misdirected Request) status code in response to the request; see <xrefsection="7.4" sectionFormat="of" target="SEMANTICS" format="default"/>.</t>section='7.4' sectionFormat='of' target='RFC9110'/>.</t> </section> </section> <sectionanchor="http-request-lifecycle" numbered="true" toc="default"> <name>HTTP Request Lifecycle</name>anchor='http-request-lifecycle'> <name>Expressing HTTP Semantics in HTTP/3</name> <sectionanchor="request-response" numbered="true" toc="default">anchor='request-response'> <name>HTTP MessageExchanges</name>Framing</name> <t>A client sends an HTTP request on arequest stream,<xref format='none' target='request-streams'>request stream</xref><iref item='request stream'/>, which is a client-initiated bidirectional QUIC stream; see <xreftarget="request-streams" format="default"/>.target='request-streams'/>. A clientMUST<bcp14>MUST</bcp14> send only a single request on a given stream. A server sends zero or more interim HTTP responses on the same stream as the request, followed by a single final HTTP response, as detailed below. See <xrefsection="15" sectionFormat="of" target="SEMANTICS" format="default"/>section='15' sectionFormat='of' target='RFC9110'/> for a description of interim and final HTTP responses.</t> <t>Pushed responses are sent on a server-initiated unidirectional QUIC stream; see <xreftarget="push-streams" format="default"/>.target='push-streams'/>. A server sends zero or more interim HTTP responses, followed by a single final HTTP response, in the same manner as a standard response. Push is described in more detail in <xreftarget="server-push" format="default"/>.</t>target='server-push'/>.</t> <t>On a given stream, receipt of multiple requests or receipt of an additional HTTP response following a final HTTP responseMUST<bcp14>MUST</bcp14> be treated asmalformed (<xref target="malformed" format="default"/>).</t><xref format='none' target='malformed'>malformed</xref><iref item='malformed'/>.</t> <t>An HTTP message (request or response) consists of:</t> <olspacing="normal" type="1"><li>thespacing='normal' type='1'> <li>the header section, including message control data, sent as a singleHEADERS frame (see<xreftarget="frame-headers" format="default"/>),</li>format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> frame,</li> <li>optionally, the content, if present, sent as a series ofDATA frames (see<xreftarget="frame-data" format="default"/>),format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frames, and</li> <li>optionally, the trailer section, if present, sent as a singleHEADERS<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> frame.</li> </ol> <t>Header and trailer sections are described in Sections <xreftarget="SEMANTICS" section="6.3" sectionFormat="bare" format="default"/>section='6.3' sectionFormat='bare' target='RFC9110'/> and <xreftarget="SEMANTICS" section="6.5" sectionFormat="bare" format="default"/>section='6.5' sectionFormat='bare' target='RFC9110'/> of <xreftarget="SEMANTICS" format="default"/>;target='RFC9110'/>; the content is described in <xrefsection="6.4" sectionFormat="of" target="SEMANTICS" format="default"/>.</t>section='6.4' sectionFormat='of' target='RFC9110'/>.</t> <t>Receipt of an invalid sequence of framesMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED; see<xreftarget="errors" format="default"/>.format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>. In particular, aDATA<xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frame before anyHEADERS<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> frame, or aHEADERS<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> orDATA<xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frame after the trailingHEADERS<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> frame, is considered invalid. Other frame types, especially unknown frame types, might be permitted subject to their own rules; see <xreftarget="extensions" format="default"/>.</t>target='extensions'/>.</t> <t>A serverMAY<bcp14>MAY</bcp14> send one or morePUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frames(<xref target="frame-push-promise" format="default"/>)before, after, or interleaved with the frames of a response message. ThesePUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frames are not part of the response; see <xreftarget="server-push" format="default"/>target='server-push'/> for more details.PUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frames are not permitted onpush streams;<xref format='none' target='push-streams'>push streams</xref><iref item='push stream'/>; a pushed response that includesPUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> framesMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED; see<xreftarget="errors" format="default"/>.</t>format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> <t>Frames of unknown types (<xreftarget="extensions" format="default"/>),target='extensions'/>), including reserved frames (<xreftarget="frame-reserved" format="default"/>) MAYtarget='frame-reserved'/>) <bcp14>MAY</bcp14> be sent on a request orpush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> before, after, or interleaved with other frames described in this section.</t> <t>TheHEADERS<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> andPUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frames might reference updates to the QPACK dynamic table. While these updates are not directly part of the message exchange, they must be received and processed before the message can be consumed. See <xreftarget="header-formatting" format="default"/>target='header-formatting'/> for more details.</t> <t>Transfer codings (see <xrefsection="6.1" sectionFormat="of" target="HTTP11" format="default"/>)section='7' sectionFormat='of' target='RFC9112'/>) are not defined for HTTP/3; the Transfer-Encoding header fieldMUST NOT<bcp14>MUST NOT</bcp14> be used.</t> <t>A responseMAY<bcp14>MAY</bcp14> consist of multiple messages when and only when one or more interim responses (1xx; see <xrefsection="15.2" sectionFormat="of" target="SEMANTICS" format="default"/>)section='15.2' sectionFormat='of' target='RFC9110'/>) precede a final response to the same request. Interim responses do not contain content or trailer sections.</t> <t>An HTTP request/response exchange fully consumes a client-initiated bidirectional QUIC stream. After sending a request, a clientMUST<bcp14>MUST</bcp14> close the stream for sending. Unless using the CONNECT method (see <xreftarget="connect" format="default"/>),target='connect'/>), clientsMUST NOT<bcp14>MUST NOT</bcp14> make stream closure dependent on receiving a response to their request. After sending a final response, the serverMUST<bcp14>MUST</bcp14> close the stream for sending. At this point, the QUIC stream is fully closed.</t> <t>When a stream is closed, this indicates the end of the final HTTP message. Because some messages are large or unbounded, endpointsSHOULD<bcp14>SHOULD</bcp14> begin processing partial HTTP messages once enough of the message has been received to make progress. If a client-initiated stream terminates without enough of the HTTP message to provide a complete response, the serverSHOULD<bcp14>SHOULD</bcp14> abort its response stream with the error codeH3_REQUEST_INCOMPLETE; see<xreftarget="errors" format="default"/>.</t>format='none' target='H3_REQUEST_INCOMPLETE'>H3_REQUEST_INCOMPLETE</xref><iref item='H3_REQUEST_INCOMPLETE'/>.</t> <t>A server can send a complete response prior to the client sending an entire request if the response does not depend on any portion of the request that has not been sent and received. When the server does not need to receive the remainder of the request, itMAY<bcp14>MAY</bcp14> abort reading therequest stream,<xref format='none' target='request-streams'>request stream</xref><iref item='request stream'/>, send a complete response, and cleanly close the sending part of the stream. The error codeH3_NO_ERROR SHOULD<xref format='none' target='H3_NO_ERROR'>H3_NO_ERROR</xref><iref item='H3_NO_ERROR'/> <bcp14>SHOULD</bcp14> be used when requesting that the client stop sending on therequest stream.<xref format='none' target='request-streams'>request stream</xref><iref item='request stream'/>. ClientsMUST NOT<bcp14>MUST NOT</bcp14> discard complete responses as a result of having their request terminated abruptly, though clients can always discard responses at their discretion for other reasons. If the server sends a partial or complete response but does not abort reading the request, clientsSHOULD<bcp14>SHOULD</bcp14> continue sending thebodycontent of the request and close the stream normally.</t> <sectionanchor="header-formatting" numbered="true" toc="default"> <name>Field Formattinganchor='request-cancellation'> <name>Request Cancellation andCompression</name>Rejection</name> <t>Once a <xref format='none' target='request-streams'>request stream</xref><iref item='request stream'/> has been opened, the request <bcp14>MAY</bcp14> be cancelled by either endpoint. Clients cancel requests if the response is no longer of interest; servers cancel requests if they are unable to or choose not to respond. When possible, it is <bcp14>RECOMMENDED</bcp14> that servers send an HTTP response with an appropriate status code rather than cancelling a request it has already begun processing.</t> <t>Implementations <bcp14>SHOULD</bcp14> cancel requests by abruptly terminating any directions of a stream that are still open. To do so, an implementation resets the sending parts of streams and aborts reading on the receiving parts of streams; see <xref section='2.4' sectionFormat='of' target='QUIC-TRANSPORT'/>.</t> <t>When the server cancels a request without performing any application processing, the request is considered "rejected". The server <bcp14>SHOULD</bcp14> abort its response stream with the error code <xref format='none' target='H3_REQUEST_REJECTED'>H3_REQUEST_REJECTED</xref><iref item='H3_REQUEST_REJECTED'/>. In this context, "processed" means that some data from the stream was passed to some higher layer of software that might have taken some action as a result. The client can treat requests rejected by the server as though they had never been sent at all, thereby allowing them to be retried later.</t> <t>Servers <bcp14>MUST NOT</bcp14> use the <xref format='none' target='H3_REQUEST_REJECTED'>H3_REQUEST_REJECTED</xref><iref item='H3_REQUEST_REJECTED'/> error code for requests that were partially or fully processed. When a server abandons a response after partial processing, it <bcp14>SHOULD</bcp14> abort its response stream with the error code <xref format='none' target='H3_REQUEST_CANCELLED'>H3_REQUEST_CANCELLED</xref><iref item='H3_REQUEST_CANCELLED'/>.</t> <t>Client <bcp14>SHOULD</bcp14> use the error code <xref format='none' target='H3_REQUEST_CANCELLED'>H3_REQUEST_CANCELLED</xref><iref item='H3_REQUEST_CANCELLED'/> to cancel requests. Upon receipt of this error code, a server <bcp14>MAY</bcp14> abruptly terminate the response using the error code <xref format='none' target='H3_REQUEST_REJECTED'>H3_REQUEST_REJECTED</xref><iref item='H3_REQUEST_REJECTED'/> if no processing was performed. Clients <bcp14>MUST NOT</bcp14> use the <xref format='none' target='H3_REQUEST_REJECTED'>H3_REQUEST_REJECTED</xref><iref item='H3_REQUEST_REJECTED'/> error code, except when a server has requested closure of the <xref format='none' target='request-streams'>request stream</xref><iref item='request stream'/> with this error code.</t> <t>If a stream is cancelled after receiving a complete response, the client <bcp14>MAY</bcp14> ignore the cancellation and use the response. However, if a stream is cancelled after receiving a partial response, the response <bcp14>SHOULD NOT</bcp14> be used. Only idempotent actions such as GET, PUT, or DELETE can be safely retried; a client <bcp14>SHOULD NOT</bcp14> automatically retry a request with a non-idempotent method unless it has some means to know that the request semantics are idempotent independent of the method or some means to detect that the original request was never applied. See <xref section='9.2.2' sectionFormat='of' target='RFC9110'/> for more details.</t> </section> <section anchor='malformed'> <name>Malformed Requests and Responses</name><iref item='malformed' primary='true'/> <t>A malformed request or response is one that is an otherwise valid sequence of frames but is invalid due to:</t> <ul spacing='normal'> <li>the presence of prohibited fields or pseudo-header fields,</li> <li>the absence of mandatory pseudo-header fields,</li> <li>invalid values for pseudo-header fields,</li> <li>pseudo-header fields after fields,</li> <li>an invalid sequence of HTTP messages,</li> <li>the inclusion of uppercase field names, or</li> <li>the inclusion of invalid characters in field names or values.</li> </ul> <t>A request or response that is defined as having content when it contains a Content-Length header field (<xref section='8.6' sectionFormat='of' target='RFC9110'/>) is malformed if the value of the Content-Length header field does not equal the sum of the <xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frame lengths received. A response that is defined as never having content, even when a Content-Length is present, can have a non-zero Content-Length header field even though no content is included in <xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frames.</t> <t>Intermediaries that process HTTP requests or responses (i.e., any intermediary not acting as a tunnel) <bcp14>MUST NOT</bcp14> forward a malformed request or response. Malformed requests or responses that are detected <bcp14>MUST</bcp14> be treated as a <xref format='none' target='errors'>stream error</xref><iref item='stream error'/> of type <xref format='none' target='H3_MESSAGE_ERROR'>H3_MESSAGE_ERROR</xref><iref item='H3_MESSAGE_ERROR'/>.</t> <t>For malformed requests, a server <bcp14>MAY</bcp14> send an HTTP response indicating the error prior to closing or resetting the stream. Clients <bcp14>MUST NOT</bcp14> accept a malformed response. Note that these requirements are intended to protect against several types of common attacks against HTTP; they are deliberately strict because being permissive can expose implementations to these vulnerabilities.</t> </section> </section> <section anchor='header-formatting'> <name>HTTP Fields</name> <t>HTTP messages carry metadata as a series of key-value pairs calledHTTP fields;"HTTP fields"; see Sections <xreftarget="SEMANTICS" section="6.3" sectionFormat="bare" format="default"/>section='6.3' sectionFormat='bare' target='RFC9110'/> and <xreftarget="SEMANTICS" section="6.5" sectionFormat="bare" format="default"/>section='6.5' sectionFormat='bare' target='RFC9110'/> of <xreftarget="SEMANTICS" format="default"/>.target='RFC9110'/>. For a listing of registered HTTP fields, see the "Hypertext Transfer Protocol (HTTP) Field Name Registry" maintained at <ereftarget="https://www.iana.org/assignments/http-fields/"/>.</t> <ul empty="true" spacing="normal"> <li> <strong>Note:</strong> This registry will not exist until <xref target="SEMANTICS" format="default"/> is approved. <strong>RFC Editor</strong>, please remove this note priorbrackets='angle' target='https://www.iana.org/assignments/http-fields/'/>. Like HTTP/2, HTTP/3 has additional considerations related topublication.</li> </ul>the use of characters in field names, the Connection header field, and pseudo-header fields.</t> <t>Field names are strings containing a subset of ASCII characters. Properties of HTTP field names and values are discussed in more detail in <xrefsection="5.1" sectionFormat="of" target="SEMANTICS" format="default"/>. As in HTTP/2, characterssection='5.1' sectionFormat='of' target='RFC9110'/>. Characters in field namesMUST<bcp14>MUST</bcp14> be converted to lowercase prior to their encoding. A request or response containing uppercase characters in field namesMUST<bcp14>MUST</bcp14> be treated asmalformed (<xref target="malformed" format="default"/>).</t> <t>Like HTTP/2, HTTP/3<xref format='none' target='malformed'>malformed</xref><iref item='malformed'/>.</t> <t>HTTP/3 does not use the Connection header field to indicate connection-specific fields; in this protocol, connection-specific metadata is conveyed by other means. An endpointMUST NOT<bcp14>MUST NOT</bcp14> generate an HTTP/3 field section containing connection-specific fields; any message containing connection-specific fieldsMUST<bcp14>MUST</bcp14> be treated asmalformed (<xref target="malformed" format="default"/>).</t><xref format='none' target='malformed'>malformed</xref><iref item='malformed'/>.</t> <t>The only exception to this is the TE header field, whichMAY<bcp14>MAY</bcp14> be present in an HTTP/3 request header; when it is, itMUST NOT<bcp14>MUST NOT</bcp14> contain any value other than "trailers".</t> <t>An intermediary transforming an HTTP/1.x message to HTTP/3MUST<bcp14>MUST</bcp14> remove connection-specific header fields as discussed in <xrefsection="7.6.1" sectionFormat="of" target="SEMANTICS" format="default"/>,section='7.6.1' sectionFormat='of' target='RFC9110'/>, or their messages will be treated by other HTTP/3 endpoints asmalformed<xref format='none' target='malformed'>malformed</xref><iref item='malformed'/>.</t> <section anchor='field-compression'> <name>Field Compression</name> <t><xref target='RFC9204'/> describes a variation of HPACK that gives an encoder some control over how much head-of-line blocking can be caused by compression. This allows an encoder to balance compression efficiency with latency. HTTP/3 uses QPACK to compress header and trailer sections, including the control data present in the header section.</t> <t>To allow for better compression efficiency, the Cookie header field (<xreftarget="malformed" format="default"/>).</t>target='COOKIES'/>) <bcp14>MAY</bcp14> be split into separate field lines, each with one or more cookie-pairs, before compression. If a decompressed field section contains multiple cookie field lines, these <bcp14>MUST</bcp14> be concatenated into a single byte string using the two-byte delimiter of "<tt>; </tt>" (ASCII 0x3b, 0x20) before being passed into a context other than HTTP/2 or HTTP/3, such as an HTTP/1.1 connection, or a generic HTTP server application.</t> </section> <sectionanchor="pseudo-header-fields" numbered="true" toc="default"> <name>Pseudo-Header Fields</name>anchor='header-size-constraints'> <name>Header Size Constraints</name> <t>An HTTP/3 implementation <bcp14>MAY</bcp14> impose a limit on the maximum size of the message header it will accept on an individual HTTP message. A server that receives a larger header section than it is willing to handle can send an HTTP 431 (Request Header Fields Too Large) status code (<xref target='RFC6585'/>). A client can discard responses that it cannot process. The size of a field list is calculated based on the uncompressed size of fields, including the length of the name and value in bytes plus an overhead of 32 bytes for each field.</t> <t>If an implementation wishes to advise its peer of this limit, it can be conveyed as a number of bytes in the <xref format='none' target='SETTINGS_MAX_FIELD_SECTION_SIZE'>SETTINGS_MAX_FIELD_SECTION_SIZE</xref><iref item='SETTINGS_MAX_FIELD_SECTION_SIZE'/> parameter. An implementation that has received this parameter <bcp14>SHOULD NOT</bcp14> send an HTTP message header that exceeds the indicated size, as the peer will likely refuse to process it. However, an HTTP message can traverse one or more intermediaries before reaching the origin server; see <xref section='3.7' sectionFormat='of' target='RFC9110'/>. Because this limit is applied separately by each implementation that processes the message, messages below this limit are not guaranteed to be accepted.</t> </section> </section> <section anchor='http-control-data'> <name>HTTP Control Data</name> <t>Like HTTP/2, HTTP/3 employs a series of pseudo-headerfieldsfields, where the field name begins with the':'<tt>:</tt> character (ASCII 0x3a). These pseudo-header fields conveythe target URI, the method of the request, and the status code for the response.</t>message control data; see <xref section='6.2' sectionFormat='of' target='RFC9110'/>.</t> <t>Pseudo-header fields are not HTTP fields. EndpointsMUST NOT<bcp14>MUST NOT</bcp14> generate pseudo-header fields other than those defined in thisdocument; however,document. However, an extension could negotiate a modification of this restriction; see <xreftarget="extensions" format="default"/>.</t>target='extensions'/>.</t> <t>Pseudo-header fields are only valid in the context in which they are defined. Pseudo-header fields defined for requestsMUST NOT<bcp14>MUST NOT</bcp14> appear in responses; pseudo-header fields defined for responsesMUST NOT<bcp14>MUST NOT</bcp14> appear in requests. Pseudo-header fieldsMUST NOT<bcp14>MUST NOT</bcp14> appear in trailer sections. EndpointsMUST<bcp14>MUST</bcp14> treat a request or response that contains undefined or invalid pseudo-header fields asmalformed (<xref target="malformed" format="default"/>).</t><xref format='none' target='malformed'>malformed</xref><iref item='malformed'/>.</t> <t>All pseudo-header fieldsMUST<bcp14>MUST</bcp14> appear in the header section before regular header fields. Any request or response that contains a pseudo-header field that appears in a header section after a regular header fieldMUST<bcp14>MUST</bcp14> be treated asmalformed (<xref target="malformed" format="default"/>).</t><xref format='none' target='malformed'>malformed</xref><iref item='malformed'/>.</t> <section anchor='request-pseudo-header-fields'> <name>Request Pseudo-Header Fields</name> <t>The following pseudo-header fields are defined for requests:</t> <dl><dt> ":method": </dt><dt>":method":</dt> <dd> <t>Contains the HTTP method (<xrefsection="9" sectionFormat="of" target="SEMANTICS" format="default"/>)</t> </dd> <dt> ":scheme": </dt>section='9' sectionFormat='of' target='RFC9110'/>)</t> </dd> <dt>":scheme":</dt> <dd> <t>Contains the scheme portion of the target URI (<xrefsection="3.1" sectionFormat="of" target="URI" format="default"/>)</t>section='3.1' sectionFormat='of' target='URI'/>).</t> </dd> <dt/> <dd><t>":scheme"<t>The :scheme pseudo-header is not restricted to URIs with scheme "http" and "https". A proxy or gateway can translate requests for non-HTTP schemes, enabling the use of HTTP to interact with non-HTTP services.</t> </dd> <dt/> <dd> <t>See <xreftarget="other-schemes" format="default"/>target='other-schemes'/> for guidance on using a scheme other than "https".</t> </dd><dt> ":authority": </dt><dt>":authority":</dt> <dd> <t>Contains the authority portion of the target URI (<xrefsection="3.2" sectionFormat="of" target="URI" format="default"/>).section='3.2' sectionFormat='of' target='URI'/>). The authorityMUST NOT<bcp14>MUST NOT</bcp14> include the deprecated"userinfo"userinfo subcomponent for URIs of scheme "http" or "https".</t> </dd> <dt/> <dd> <t>To ensure that the HTTP/1.1 request line can be reproduced accurately, this pseudo-header fieldMUST<bcp14>MUST</bcp14> be omitted when translating from an HTTP/1.1 request that has a request target inorigin or asteriska method-specific form; see <xrefsection="7.1" sectionFormat="of" target="SEMANTICS" format="default"/>.section='7.1' sectionFormat='of' target='RFC9110'/>. Clients that generate HTTP/3 requests directlySHOULD<bcp14>SHOULD</bcp14> use the":authority":authority pseudo-header field instead of the Host header field. An intermediary that converts an HTTP/3 request to HTTP/1.1MUST<bcp14>MUST</bcp14> create a Host field if one is not present in a request by copying the value of the":authority":authority pseudo-header field.</t> </dd><dt> ":path": </dt><dt>":path":</dt> <dd> <t>Contains the path and query parts of the target URI (the "path-absolute" production and optionally a'?'<tt>?</tt> character (ASCII 0x3f) followed by the "query" production; see Sections <xreftarget="URI" section="3.3" sectionFormat="bare" format="default"/>section='3.3' sectionFormat='bare' target='URI'/> and <xreftarget="URI" section="3.4" sectionFormat="bare" format="default"/>section='3.4' sectionFormat='bare' target='URI'/> of <xreftarget="URI" format="default"/>. A request in asterisk form includes the value '*' for the ":path" pseudo-header field.</t>target='URI'/>.</t> </dd> <dt/> <dd> <t>This pseudo-header fieldMUST NOT<bcp14>MUST NOT</bcp14> be empty for "http" or "https" URIs; "http" or "https" URIs that do not contain a path componentMUST<bcp14>MUST</bcp14> include a value of'/'. The exception to this rule is an<tt>/</tt> (ASCII 0x2f). An OPTIONS requestfor an "http" or "https" URIthat does not include a pathcomponent; these MUST include a ":path" pseudo-header field with acomponent includes the valueof '*';<tt>*</tt> (ASCII 0x2a) for the :path pseudo-header field; see <xrefsection="7.1" sectionFormat="of" target="SEMANTICS" format="default"/>.</t>section='7.1' sectionFormat='of' target='RFC9110'/>.</t> </dd> </dl> <t>All HTTP/3 requestsMUST<bcp14>MUST</bcp14> include exactly one value for the":method", ":scheme",:method, :scheme, and":path":path pseudo-header fields, unlessitthe request is a CONNECT request; see <xreftarget="connect" format="default"/>.</t>target='connect'/>.</t> <t>If the":scheme":scheme pseudo-header field identifies a scheme that has a mandatory authority component (including "http" and "https"), the requestMUST<bcp14>MUST</bcp14> contain either an":authority":authority pseudo-header field or a"Host"Host header field. If these fields are present, theyMUST NOT<bcp14>MUST NOT</bcp14> be empty. If both fields are present, theyMUST<bcp14>MUST</bcp14> contain the same value. If the scheme does not have a mandatory authority component and none is provided in the request target, the requestMUST NOT<bcp14>MUST NOT</bcp14> contain the":authority":authority pseudo-header or"Host"Host header fields.</t> <t>An HTTP request that omits mandatory pseudo-header fields or contains invalid values for those pseudo-header fields ismalformed (<xref target="malformed" format="default"/>).</t><xref format='none' target='malformed'>malformed</xref><iref item='malformed'/>.</t> <t>HTTP/3 does not define a way to carry the version identifier that is included in the HTTP/1.1 requestline.</t>line. HTTP/3 requests implicitly have a protocol version of "3.0".</t> </section> <section anchor='response-pseudo-header-fields'> <name>Response Pseudo-Header Fields</name> <t>For responses, a single ":status" pseudo-header field is defined that carries the HTTP status code; see <xrefsection="15" sectionFormat="of" target="SEMANTICS" format="default"/>.section='15' sectionFormat='of' target='RFC9110'/>. This pseudo-header fieldMUST<bcp14>MUST</bcp14> be included in all responses; otherwise, the response ismalformed (<xref target="malformed" format="default"/>).</t><xref format='none' target='malformed'>malformed</xref><iref item='malformed'/> (see <xref target='malformed'/>).</t> <t>HTTP/3 does not define a way to carry the version or reason phrase that is included in an HTTP/1.1 statusline.</t> </section> <section anchor="field-compression" numbered="true" toc="default"> <name>Field Compression</name> <t><xref target="QPACK" format="default"/> describes a variation of HPACK that gives an encoder some control over how much head-of-line blocking can be caused by compression. This allows an encoder to balance compression efficiency with latency.line. HTTP/3uses QPACK to compress header and trailer sections, including the pseudo-header fields present in the header section.</t> <t>To allow for better compression efficiency, the "Cookie" field (<xref target="RFC6265" format="default"/>) MAY be split into separate field lines, each with one or more cookie-pairs, before compression. If a decompressed field section contains multiple cookie field lines, these MUST be concatenated into a single byte string using the two-byte delimiter of 0x3b, 0x20 (the ASCII string "; ") before being passed into a context other than HTTP/2 or HTTP/3, such as an HTTP/1.1 connection, or a generic HTTP server application.</t> </section> <section anchor="header-size-constraints" numbered="true" toc="default"> <name>Header Size Constraints</name> <t>An HTTP/3 implementation MAY impose a limit on the maximum size of the message header it will accept on an individual HTTP message. A server that receives a larger header section than it is willing to handle can send an HTTP 431 (Request Header Fields Too Large) status code (<xref target="RFC6585" format="default"/>). A client can discardresponsesthat it cannot process. The size of a field list is calculated based on the uncompressed size of fields, including the length of the name and value in bytes plus an overhead of 32 bytes for each field.</t> <t>If an implementation wishes to advise its peer of this limit, it can be conveyed as a number of bytes in the SETTINGS_MAX_FIELD_SECTION_SIZE parameter. An implementation that has received this parameter SHOULD NOT send an HTTP message header that exceeds the indicated size, as the peer will likely refuse to process it. However, an HTTP message can traverse one or more intermediaries before reaching the origin server; see <xref section="3.7" sectionFormat="of" target="SEMANTICS" format="default"/>. Because this limit is applied separately by each implementation which processes the message, messages below this limit are not guaranteed to be accepted.</t> </section> </section> <section anchor="request-cancellation" numbered="true" toc="default"> <name>Request Cancellation and Rejection</name> <t>Once a request stream has been opened, the request MAY be cancelled by either endpoint. Clients cancel requests if the response is no longer of interest; servers cancel requests if they are unable to or choose not to respond. When possible, it is RECOMMENDED that servers send an HTTP response with an appropriate status code rather than canceling a request it has already begun processing.</t> <t>Implementations SHOULD cancel requests by abruptly terminating any directions of a stream that are still open. This means resetting the sending parts of streams and aborting reading on receiving parts of streams; see <xref section="2.4" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>.</t> <t>When the server cancels a request without performing any application processing, the request is considered "rejected." The server SHOULD abort its response stream with the error code H3_REQUEST_REJECTED. In this context, "processed" means that some data from the stream was passed to some higher layer of software that might have taken some action as a result. The client can treat requests rejected by the server as though they had never been sent at all, thereby allowing them to be retried later.</t> <t>Servers MUST NOT use the H3_REQUEST_REJECTED error code for requests that were partially or fully processed. When a server abandons a response after partial processing, it SHOULD abort its response stream with the error code H3_REQUEST_CANCELLED.</t> <t>Client SHOULD use the error code H3_REQUEST_CANCELLED to cancel requests. Upon receipt of this error code, a server MAY abruptly terminate the response using the error code H3_REQUEST_REJECTED if no processing was performed. Clients MUST NOT use the H3_REQUEST_REJECTED error code, except when a server has requested closure of the request stream with this error code.</t> <t>If a stream is canceled after receiving a complete response, the client MAY ignore the cancellation and use the response. However, if a stream is cancelled after receiving a partial response, the response SHOULD NOT be used. Only idempotent actions such as GET, PUT, or DELETE can be safely retried; a client SHOULD NOT automatically retry a request with a non-idempotent method unless it has some means to know that the request semantics are idempotent independent of the method or some means to detect that the original request was never applied. See <xref section="9.2.2" sectionFormat="of" target="SEMANTICS" format="default"/> for more details.</t> </section> <section anchor="malformed" numbered="true" toc="default"> <name>Malformed Requests and Responses</name> <t>A malformed request or response is one that is an otherwise valid sequence of frames but is invalid due to:</t> <ul spacing="normal"> <li>the presence of prohibited fields or pseudo-header fields,</li> <li>the absence of mandatory pseudo-header fields,</li> <li>invalid values for pseudo-header fields,</li> <li>pseudo-header fields after fields,</li> <li>an invalid sequence of HTTP messages,</li> <li>the inclusion of uppercase field names, or</li> <li>the inclusion of invalid characters in field names or values.</li> </ul> <t>A request or response that is defined as having content when it contains a Content-Length header field (<xref section="6.4.1" sectionFormat="of" target="SEMANTICS" format="default"/>), is malformed if the value of a Content-Length header field does not equal the sum of the DATA frame lengths received. A response that is defined as never having content, even when a Content-Length is present, canimplicitly have anon-zero Content-Length field even though no content is included in DATA frames.</t> <t>Intermediaries that process HTTP requests or responses (i.e., any intermediary not acting as a tunnel) MUST NOT forward a malformed request or response. Malformed requests or responses that are detected MUST be treated as a stream error (<xref target="errors" format="default"/>) of type H3_MESSAGE_ERROR.</t> <t>For malformed requests, a server MAY send an HTTP response indicating the error prior to closing or resetting the stream. Clients MUST NOT accept a malformed response. Note that these requirements are intended to protect against several typesprotocol version ofcommon attacks against HTTP; they are deliberately strict because being permissive can expose implementations to these vulnerabilities.</t>"3.0".</t> </section> </section> <sectionanchor="connect" numbered="true" toc="default">anchor='connect'> <name>The CONNECT Method</name> <t>The CONNECT method requests that the recipient establish a tunnel to the destination origin server identified by the request-target; see <xrefsection="9.3.6" sectionFormat="of" target="SEMANTICS" format="default"/>.section='9.3.6' sectionFormat='of' target='RFC9110'/>. It is primarily used with HTTP proxies to establish a TLS session with an origin server for the purposes of interacting with "https" resources.</t> <t>In HTTP/1.x, CONNECT is used to convert an entire HTTP connection into a tunnel to a remote host. In HTTP/2 and HTTP/3, the CONNECT method is used to establish a tunnel over a single stream.</t> <t>A CONNECT requestMUST<bcp14>MUST</bcp14> be constructed as follows:</t> <ulspacing="normal">spacing='normal'> <li>The":method":method pseudo-header field is set to "CONNECT"</li> <li>The":scheme":scheme and":path":path pseudo-header fields are omitted</li> <li>The":authority":authority pseudo-header field contains the host and port to connect to (equivalent to the authority-form of the request-target of CONNECT requests; see <xrefsection="7.1" sectionFormat="of" target="SEMANTICS" format="default"/>)</li>section='7.1' sectionFormat='of' target='RFC9110'/>).</li> </ul> <t>Therequest stream<xref format='none' target='request-streams'>request stream</xref><iref item='request stream'/> remains open at the end of the request to carry the data to be transferred. A CONNECT request that does not conform to these restrictions ismalformed; see<xreftarget="malformed" format="default"/>.</t>format='none' target='malformed'>malformed</xref><iref item='malformed'/>.</t> <t>A proxy that supports CONNECT establishes a TCP connection (<xreftarget="RFC0793" format="default"/>)target='RFC0793'/>) to the server identified in the":authority":authority pseudo-header field. Once this connection is successfully established, the proxy sends aHEADERS<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> frame containing a 2xx series status code to the client, as defined in <xrefsection="15.3" sectionFormat="of" target="SEMANTICS" format="default"/>.</t>section='15.3' sectionFormat='of' target='RFC9110'/>.</t> <t>AllDATA<xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frames on the stream correspond to data sent or received on the TCP connection. The payload of anyDATA<xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frame sent by the client is transmitted by the proxy to the TCP server; data received from the TCP server is packaged intoDATA<xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frames by the proxy. Note that the size and number of TCP segments is not guaranteed to map predictably to the size and number of HTTPDATA<xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> or QUIC STREAM frames.</t> <t>Once the CONNECT method has completed, onlyDATA<xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frames are permitted to be sent on the stream. Extension framesMAY<bcp14>MAY</bcp14> be used if specifically permitted by the definition of the extension. Receipt of any other known frame typeMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED; see<xreftarget="errors" format="default"/>.</t>format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> <t>The TCP connection can be closed by either peer. When the client ends therequest stream<xref format='none' target='request-streams'>request stream</xref><iref item='request stream'/> (that is, the receive stream at the proxy enters the "Data Recvd" state), the proxy will set the FIN bit on its connection to the TCP server. When the proxy receives a packet with the FIN bit set, it will close the send stream that it sends to the client. TCP connections that remainhalf-closedhalf closed in a single direction are not invalid, but are often handled poorly by servers, so clientsSHOULD NOT<bcp14>SHOULD NOT</bcp14> close a stream for sending while they still expect to receive data from the target of the CONNECT.</t> <t>A TCPconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> is signaled by abruptly terminating the stream. A proxy treats any error in the TCP connection, which includes receiving a TCP segment with the RST bit set, as astream error<xref format='none' target='errors'>stream error</xref><iref item='stream error'/> of typeH3_CONNECT_ERROR; see<xreftarget="errors" format="default"/>. Correspondingly,format='none' target='H3_CONNECT_ERROR'>H3_CONNECT_ERROR</xref><iref item='H3_CONNECT_ERROR'/>.</t> <t>Correspondingly, if a proxy detects an error with the stream or the QUIC connection, itMUST<bcp14>MUST</bcp14> close the TCP connection. If the proxy detects that the client has reset the stream or aborted reading from the stream, it <bcp14>MUST</bcp14> close the TCP connection. If the stream is reset or reading is aborted by the client, a proxy <bcp14>SHOULD</bcp14> perform the same operation on the other direction in order to ensure that both directions of the stream are cancelled. In all these cases, if the underlying TCP implementation permits it, the proxySHOULD<bcp14>SHOULD</bcp14> send a TCP segment with the RST bit set.</t> <t>Since CONNECT creates a tunnel to an arbitrary server, proxies that support CONNECTSHOULD<bcp14>SHOULD</bcp14> restrict its use to a set of known ports or a list of safe request targets; see <xrefsection="9.3.6" sectionFormat="of" target="SEMANTICS" format="default"/>section='9.3.6' sectionFormat='of' target='RFC9110'/> for moredetail.</t>details.</t> </section> <sectionanchor="http-upgrade" numbered="true" toc="default">anchor='http-upgrade'> <name>HTTP Upgrade</name> <t>HTTP/3 does not support the HTTP Upgrade mechanism (<xrefsection="7.8" sectionFormat="of" target="SEMANTICS" format="default"/>)section='7.8' sectionFormat='of' target='RFC9110'/>) or the 101 (Switching Protocols) informational status code (<xrefsection="15.2.2" sectionFormat="of" target="SEMANTICS" format="default"/>).</t>section='15.2.2' sectionFormat='of' target='RFC9110'/>).</t> </section> <sectionanchor="server-push" numbered="true" toc="default">anchor='server-push'> <name>ServerPush</name>Push</name><iref item='push ID' primary='true'/> <t>Server push is an interaction mode that permits a server to push a request-response exchange to a client in anticipation of the client making the indicated request. This trades off network usage against a potential latency gain. HTTP/3 server push is similar to what is described in <xrefsection="8.2" sectionFormat="of" target="HTTP2" format="default"/>,section='8.2' sectionFormat='of' target='RFC9113'/>, but it uses different mechanisms.</t> <t>Each server push is assigned a uniquePushpush ID by the server. ThePushpush ID is used to refer to the push in various contexts throughout the lifetime of the HTTP/3 connection.</t> <t>ThePushpush ID space begins atzero,zero and ends at a maximum value set by theMAX_PUSH_ID frame; see<xreftarget="frame-max-push-id" format="default"/>.format='none' target='frame-max-push-id'>MAX_PUSH_ID</xref><iref item='MAX_PUSH_ID'/> frame. In particular, a server is not able to push until after the client sends aMAX_PUSH_ID<xref format='none' target='frame-max-push-id'>MAX_PUSH_ID</xref><iref item='MAX_PUSH_ID'/> frame. A client sendsMAX_PUSH_ID<xref format='none' target='frame-max-push-id'>MAX_PUSH_ID</xref><iref item='MAX_PUSH_ID'/> frames to control the number of pushes that a server can promise. A serverSHOULD<bcp14>SHOULD</bcp14> usePushpush IDs sequentially, beginning from zero. A clientMUST<bcp14>MUST</bcp14> treat receipt of apush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_ID_ERROR (<xref target="errors" format="default"/>)<xref format='none' target='H3_ID_ERROR'>H3_ID_ERROR</xref><iref item='H3_ID_ERROR'/> when noMAX_PUSH_ID<xref format='none' target='frame-max-push-id'>MAX_PUSH_ID</xref><iref item='MAX_PUSH_ID'/> frame has been sent or when the stream references aPushpush ID that is greater than the maximumPushpush ID.</t> <t>ThePushpush ID is used in one or morePUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frames(<xref target="frame-push-promise" format="default"/>)that carry the control data and headersectionfields of the request message. These frames are sent on therequest stream<xref format='none' target='request-streams'>request stream</xref><iref item='request stream'/> that generated the push. This allows the server push to be associated with a client request. When the samePushpush ID is promised on multiplerequest streams,<xref format='none' target='request-streams'>request streams</xref><iref item='request stream'/>, the decompressed request field sectionsMUST<bcp14>MUST</bcp14> contain the same fields in the same order, and both the name and the value in each fieldMUST<bcp14>MUST</bcp14> be identical.</t> <t>ThePushpush ID is then included with thepush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> that ultimately fulfills thosepromises; see <xref target="push-streams" format="default"/>.promises. Thepush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> identifies thePushpush ID of the promise that it fulfills, then contains a response to the promised request as described in <xreftarget="request-response" format="default"/>.</t>target='request-response'/>.</t> <t>Finally, thePushpush ID can be used inCANCEL_PUSH<xref format='none' target='frame-cancel-push'>CANCEL_PUSH</xref><iref item='CANCEL_PUSH'/> frames; see <xreftarget="frame-cancel-push" format="default"/>.target='frame-cancel-push'/>. Clients use this frame to indicate they do not wish to receive a promised resource. Servers use this frame to indicate they will not be fulfilling a previous promise.</t> <t>Not all requests can be pushed. A serverMAY<bcp14>MAY</bcp14> push requests that have the following properties:</t> <ulspacing="normal">spacing='normal'> <li>cacheable; see <xrefsection="9.2.3" sectionFormat="of" target="SEMANTICS" format="default"/></li>section='9.2.3' sectionFormat='of' target='RFC9110'/></li> <li>safe; see <xrefsection="9.2.1" sectionFormat="of" target="SEMANTICS" format="default"/></li>section='9.2.1' sectionFormat='of' target='RFC9110'/></li> <li>does not includearequestbodycontent or a trailer section</li> </ul> <t>The serverMUST<bcp14>MUST</bcp14> include a value in the":authority":authority pseudo-header field for which the server is authoritative. If the client has not yet validated the connection for the origin indicated by the pushed request, itMUST<bcp14>MUST</bcp14> perform the same verification process it would do before sending a request for that origin on the connection; see <xreftarget="connection-reuse" format="default"/>.target='connection-reuse'/>. If this verification fails, the clientMUST NOT<bcp14>MUST NOT</bcp14> consider the server authoritative for that origin.</t> <t>ClientsSHOULD<bcp14>SHOULD</bcp14> send aCANCEL_PUSH<xref format='none' target='frame-cancel-push'>CANCEL_PUSH</xref><iref item='CANCEL_PUSH'/> frame upon receipt of aPUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frame carrying a request that is not cacheable, is not known to be safe, that indicates the presence ofarequestbody,content, or for which it does not consider the server authoritative. Any corresponding responsesMUST NOT<bcp14>MUST NOT</bcp14> be used or cached.</t> <t>Each pushed response is associated with one or more client requests. The push is associated with therequest stream<xref format='none' target='request-streams'>request stream</xref><iref item='request stream'/> on which thePUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frame was received. The same server push can be associated with additional client requests using aPUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frame with the samePushpush ID on multiplerequest streams.<xref format='none' target='request-streams'>request streams</xref><iref item='request stream'/>. These associations do not affect the operation of the protocol, butMAYthey <bcp14>MAY</bcp14> be considered by user agents when deciding how to use pushed resources.</t> <t>Ordering of aPUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frame in relation to certain parts of the response is important. The serverSHOULD<bcp14>SHOULD</bcp14> sendPUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frames prior to sendingHEADERS<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> orDATA<xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frames that reference the promised responses. This reduces the chance that a client requests a resource that will be pushed by the server.</t> <t>Due to reordering,push stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> data can arrive before the correspondingPUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frame. When a client receives a newpush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> with an as-yet-unknownPushpush ID, both the associated client request and the pushed request header fields are unknown. The client can buffer the stream data in expectation of the matchingPUSH_PROMISE.<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/>. The client can use stream flow control(see <xref section="4.1" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>)(<xref section='4.1' sectionFormat='of' target='QUIC-TRANSPORT'/>) to limit the amount of data a server may commit to the pushedstream.</t>stream. Clients <bcp14>SHOULD</bcp14> abort reading and discard data already read from <xref format='none' target='push-streams'>push streams</xref><iref item='push stream'/> if no corresponding <xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frame is processed in a reasonable amount of time.</t> <t>Push stream data can also arrive after a client hascanceledcancelled a push. In this case, the client can abort reading the stream with an error code ofH3_REQUEST_CANCELLED.<xref format='none' target='H3_REQUEST_CANCELLED'>H3_REQUEST_CANCELLED</xref><iref item='H3_REQUEST_CANCELLED'/>. This asks the server not to transfer additional data and indicates that it will be discarded upon receipt.</t> <t>Pushed responses that are cacheable (see <xrefsection="3" sectionFormat="of" target="CACHING" format="default"/>)section='3' sectionFormat='of' target='RFC9111'/>) can be stored by the client, if it implements an HTTP cache. Pushed responses are considered successfully validated on the origin server (e.g., if the "no-cache" cache response directive is present; see <xrefsection="5.2.2.3" sectionFormat="of" target="CACHING" format="default"/>)section='5.2.2.4' sectionFormat='of' target='RFC9111'/>) at the time the pushed response is received.</t> <t>Pushed responses that are not cacheableMUST NOT<bcp14>MUST NOT</bcp14> be stored by any HTTP cache. TheyMAY<bcp14>MAY</bcp14> be made available to the application separately.</t> </section> </section> <sectionanchor="connection-closure" numbered="true" toc="default">anchor='connection-closure'> <name>Connection Closure</name> <t>Once established, an HTTP/3 connection can be used for many requests and responses over time until the connection is closed. Connection closure can happen in any of several different ways.</t> <sectionanchor="idle-connections" numbered="true" toc="default">anchor='idle-connections'> <name>Idle Connections</name> <t>Each QUIC endpoint declares an idle timeout during the handshake. If the QUIC connection remains idle (no packets received) for longer than this duration, the peer will assume that the connection has been closed. HTTP/3 implementations will need to open a new HTTP/3 connection for new requests if the existing connection has been idle for longer than the idle timeout negotiated during the QUIC handshake, andSHOULDthey <bcp14>SHOULD</bcp14> do so if approaching the idle timeout; see <xrefsection="10.1" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>.</t>section='10.1' sectionFormat='of' target='QUIC-TRANSPORT'/>.</t> <t>HTTP clients are expected to request that the transport keep connections open while there are responses outstanding for requests or server pushes, as described in <xrefsection="10.1.2" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>.section='10.1.2' sectionFormat='of' target='QUIC-TRANSPORT'/>. If the client is not expecting a response from the server, allowing an idle connection to time out is preferred over expending effort maintaining a connection that might not be needed. A gatewayMAY<bcp14>MAY</bcp14> maintain connections in anticipation of need rather than incur the latency cost of connection establishment to servers. ServersSHOULD NOT<bcp14>SHOULD NOT</bcp14> actively keep connections open.</t> </section> <sectionanchor="connection-shutdown" numbered="true" toc="default">anchor='connection-shutdown'> <name>Connection Shutdown</name> <t>Even when a connection is not idle, either endpoint can decide to stop using the connection and initiate a graceful connection close. Endpoints initiate the graceful shutdown of an HTTP/3 connection by sending aGOAWAY frame (<xref target="frame-goaway" format="default"/>).<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame. TheGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame contains an identifier that indicates to the receiver the range of requests or pushes that were or might be processed in this connection. The server sends a client-initiated bidirectionalStreamstream ID; the client sends aPush ID (<xref target="server-push" format="default"/>).<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/>. Requests or pushes with the indicated identifier or greater are rejected (<xreftarget="request-cancellation" format="default"/>)target='request-cancellation'/>) by the sender of theGOAWAY.<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/>. This identifierMAY<bcp14>MAY</bcp14> be zero if no requests or pushes were processed.</t> <t>The information in theGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame enables a client and server to agree on which requests or pushes were accepted prior to the shutdown of the HTTP/3 connection. Upon sending aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame, the endpointSHOULD<bcp14>SHOULD</bcp14> explicitly cancel (see Sections <xreftarget="request-cancellation" format="default"/>format='counter' target='request-cancellation'/> and <xreftarget="frame-cancel-push" format="default"/>)format='counter' target='frame-cancel-push'/>) any requests or pushes that have identifiers greater than or equal tothatthe one indicated, in order to clean up transport state for the affected streams. The endpointSHOULD<bcp14>SHOULD</bcp14> continue to do so as more requests or pushes arrive.</t> <t>EndpointsMUST NOT<bcp14>MUST NOT</bcp14> initiate new requests or promise new pushes on the connection after receipt of aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame from the peer. ClientsMAY<bcp14>MAY</bcp14> establish a new connection to send additional requests.</t> <t>Some requests or pushes might already be in transit:</t> <ulspacing="normal">spacing='normal'> <li> <t>Upon receipt of aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame, if the client has already sent requests with aStreamstream ID greater than or equal to the identifier contained in theGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame, those requests will not be processed. Clients can safely retry unprocessed requests on a different HTTP connection. A client that is unable to retry requests loses all requests that are in flight when the server closes theconnection. </t> <t> Requestsconnection.</t> <t>Requests onStreamstream IDs less than theStreamstream ID in aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame from the server might have been processed; their status cannot be known until a response is received, the stream is reset individually, anotherGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> is received with a lowerStreamstream ID than that of the request in question, or the connectionterminates. </t> <t> Servers MAYterminates.</t> <t>Servers <bcp14>MAY</bcp14> reject individual requests on streams below the indicated ID if these requests were not processed.</t> </li> <li>If a server receives aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame after having promised pushes with aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> greater than or equal to the identifier contained in theGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame, those pushes will not be accepted.</li> </ul> <t>ServersSHOULD<bcp14>SHOULD</bcp14> send aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame when the closing of a connection is known in advance, even if the advance notice is small, so that the remote peer can know whether or not a request has been partiallyprocessed or not.processed. For example, if an HTTP client sends a POST at the same time that a server closes a QUIC connection, the client cannot know if the server started to process that POST request if the server does not send aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame to indicate what streams it might have acted on.</t> <t>An endpointMAY<bcp14>MAY</bcp14> send multipleGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frames indicating different identifiers, but the identifier in each frameMUST NOT<bcp14>MUST NOT</bcp14> be greater than the identifier in any previous frame, since clients might already have retried unprocessed requests on another HTTP connection. Receiving aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> containing a larger identifier than previously receivedMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_ID_ERROR; see<xreftarget="errors" format="default"/>.</t>format='none' target='H3_ID_ERROR'>H3_ID_ERROR</xref><iref item='H3_ID_ERROR'/>.</t> <t>An endpoint that is attempting to gracefully shut down a connection can send aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame with a value set to the maximum possible value (2<sup>62</sup>-4 for servers, 2<sup>62</sup>-1 for clients). This ensures that the peer stops creating new requests or pushes. After allowing time for any in-flight requests or pushes to arrive, the endpoint can send anotherGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame indicating which requests or pushes it might accept before the end of the connection. This ensures that a connection can be cleanly shut down without losing requests.</t> <t>A client has more flexibility in the value it chooses for the Push ID field in aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> that it sends. A value of 2<sup>62</sup>-1 indicates that the server can continue fulfilling pushes that have already been promised. A smaller value indicates the client will reject pushes withPushpush IDs greater than or equal to this value. Like the server, the clientMAY<bcp14>MAY</bcp14> send subsequentGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frames so long as the specifiedPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> is no greater than any previously sent value.</t> <t>Even when aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> indicates that a given request or push will not be processed or accepted upon receipt, the underlying transport resources still exist. The endpoint that initiated these requests can cancel them to clean up transport state.</t> <t>Once all accepted requests and pushes have been processed, the endpoint can permit the connection to become idle, orMAYit <bcp14>MAY</bcp14> initiate an immediate closure of the connection. An endpoint that completes a graceful shutdownSHOULD<bcp14>SHOULD</bcp14> use theH3_NO_ERROR<xref format='none' target='H3_NO_ERROR'>H3_NO_ERROR</xref><iref item='H3_NO_ERROR'/> error code when closing the connection.</t> <t>If a client has consumed all available bidirectional stream IDs with requests, the server need not send aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame, since the client is unable to make further requests.</t> </section> <sectionanchor="immediate-application-closure" numbered="true" toc="default">anchor='immediate-application-closure'> <name>Immediate Application Closure</name> <t>An HTTP/3 implementation can immediately close the QUIC connection at any time. This results in sending a QUIC CONNECTION_CLOSE frame to the peer indicating that the application layer has terminated the connection. The application error code in this frame indicates to the peer why the connection is being closed. See <xreftarget="errors" format="default"/>target='errors'/> for error codes that can be used when closing a connection in HTTP/3.</t> <t>Before closing the connection, aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frameMAY<bcp14>MAY</bcp14> be sent to allow the client to retry some requests. Including theGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame in the same packet as the QUIC CONNECTION_CLOSE frame improves the chances of the frame being received by clients.</t> <t>If there are open streams that have not been explicitly closed, they are implicitly closed when the connection is closed; see <xrefsection="10.2" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>.</t>section='10.2' sectionFormat='of' target='QUIC-TRANSPORT'/>.</t> </section> <sectionanchor="transport-closure" numbered="true" toc="default">anchor='transport-closure'> <name>Transport Closure</name> <t>For various reasons, the QUIC transport could indicate to the application layer that the connection has terminated. This might be due to an explicit closure by the peer, a transport-level error, or a change in network topology that interrupts connectivity.</t> <t>If a connection terminates without aGOAWAY<xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> frame, clientsMUST<bcp14>MUST</bcp14> assume that any request that was sent, whether in whole or in part, might have been processed.</t> </section> </section> <sectionanchor="stream-mapping" numbered="true" toc="default">anchor='stream-mapping'> <name>Stream Mapping and Usage</name> <t>A QUIC stream provides reliable in-order delivery of bytes, but makes no guarantees about order of delivery with regard to bytes on other streams. In version 1 of QUIC, the stream data containing HTTP frames is carried by QUIC STREAM frames, but this framing is invisible to the HTTP framing layer. The transport layer buffers and orders received stream data, exposing a reliable byte stream to the application. Although QUIC permits out-of-order delivery within a stream, HTTP/3 does not make use of this feature.</t> <t>QUIC streams can be either unidirectional, carrying data only from initiator to receiver, orbidirectional.bidirectional, carrying data in both directions. Streams can be initiated by either the client or the server. For more detail on QUIC streams, see <xrefsection="2" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>.</t>section='2' sectionFormat='of' target='QUIC-TRANSPORT'/>.</t> <t>When HTTP fields and data are sent over QUIC, the QUIC layer handles most of the stream management. HTTP does not need to do any separate multiplexing when usingQUIC -QUIC: data sent over a QUIC stream always maps to a particular HTTP transaction or to the entire HTTP/3 connection context.</t> <sectionanchor="request-streams" numbered="true" toc="default">anchor='request-streams'> <name>BidirectionalStreams</name>Streams</name><iref item='request stream' primary='true'/> <t>All client-initiated bidirectional streams are used for HTTP requests and responses. A bidirectional stream ensures that the response can be readily correlated with the request. These streams are referred to as request streams.</t> <t>This means that the client's first request occurs on QUIC stream 0, with subsequent requests onstreamstreams 4, 8, and so on. In order to permit these streams to open, an HTTP/3 serverSHOULD<bcp14>SHOULD</bcp14> configure non-zero minimum values for the number of permitted streams and the initial streamflow controlflow-control window. So as to not unnecessarily limit parallelism, at least 100 request streamsSHOULD<bcp14>SHOULD</bcp14> be permitted at a time.</t> <t>HTTP/3 does not use server-initiated bidirectional streams, though an extension could define a use for these streams. ClientsMUST<bcp14>MUST</bcp14> treat receipt of a server-initiated bidirectional stream as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_STREAM_CREATION_ERROR (<xref target="errors" format="default"/>)<xref format='none' target='H3_STREAM_CREATION_ERROR'>H3_STREAM_CREATION_ERROR</xref><iref item='H3_STREAM_CREATION_ERROR'/> unless such an extension has been negotiated.</t> </section> <sectionanchor="unidirectional-streams" numbered="true" toc="default">anchor='unidirectional-streams'> <name>Unidirectional Streams</name> <t>Unidirectional streams, in either direction, are used for a range of purposes. The purpose is indicated by a stream type, which is sent as a variable-length integer at the start of the stream. The format and structure of data that follows this integer is determined by the stream type.</t><figure anchor="fig-stream-header"><figure> <name>Unidirectional Stream Header</name> <artworktype="drawing" name="" align="left" alt=""><![CDATA[type='ascii-art'><![CDATA[ Unidirectional Stream Header { Stream Type (i), } ]]></artwork> </figure> <t>Two stream types are defined in this document:control streams<xref format='none' target='control-streams'>control streams</xref><iref item='control stream'/> (<xreftarget="control-streams" format="default"/>)target='control-streams'/>) andpush streams<xref format='none' target='push-streams'>push streams</xref><iref item='push stream'/> (<xreftarget="push-streams" format="default"/>).target='push-streams'/>). <xreftarget="QPACK" format="default"/>target='RFC9204'/> defines two additional stream types. Other stream types can be defined by extensions to HTTP/3; see <xreftarget="extensions" format="default"/>target='extensions'/> for more details. Some stream types are reserved (<xreftarget="stream-grease" format="default"/>).</t>target='stream-grease'/>).</t> <t>The performance of HTTP/3 connections in the early phase of their lifetime is sensitive to the creation and exchange of data on unidirectional streams. Endpoints that excessively restrict the number of streams or theflow controlflow-control window of these streams will increase the chance that the remote peer reaches the limit early and becomes blocked. In particular, implementations should consider that remote peers may wish to exercise reserved stream behavior (<xreftarget="stream-grease" format="default"/>)target='stream-grease'/>) with some of the unidirectional streams they are permitted touse. To avoid blocking,use.</t> <t>Each endpoint needs to create at least one unidirectional stream for the HTTP <xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>. QPACK requires two additional unidirectional streams, and other extensions might require further streams. Therefore, the transport parameters sent by both clients and serversMUST<bcp14>MUST</bcp14> allow the peer to create at leastone unidirectional stream for the HTTP control stream plus the number ofthree unidirectionalstreams required by mandatory extensions (three being the minimum number required for the base HTTP/3 protocol and QPACK), and SHOULDstreams. These transport parameters <bcp14>SHOULD</bcp14> also provide at least 1,024 bytes offlow controlflow-control credit to each unidirectional stream.</t> <t>Note that an endpoint is not required to grant additional credits to create more unidirectional streams if its peer consumes all the initial credits before creating the critical unidirectional streams. EndpointsSHOULD<bcp14>SHOULD</bcp14> create the HTTPcontrol stream<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/> as well as the unidirectional streams required by mandatory extensions (such as the QPACK encoder and decoder streams) first, and then create additional streams as allowed by their peer.</t> <t>If the stream header indicates a stream type that is not supported by the recipient, the remainder of the stream cannot be consumed as the semantics are unknown. Recipients of unknown stream typesMAY<bcp14>MUST</bcp14> either abort reading of the streamwith anor discard incoming data without further processing. If reading is aborted, the recipient <bcp14>SHOULD</bcp14> use the <xref format='none' target='H3_STREAM_CREATION_ERROR'>H3_STREAM_CREATION_ERROR</xref><iref item='H3_STREAM_CREATION_ERROR'/> error codeof H3_STREAM_CREATION_ERRORor a reserved error code (<xreftarget="http-error-codes" format="default"/>), but MUST NOTtarget='http-error-codes'/>). The recipient <bcp14>MUST NOT</bcp14> considersuch streamsunknown stream types to be aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of any kind.</t> <t>As certain stream types can affect connection state, a recipient <bcp14>SHOULD NOT</bcp14> discard data from incoming unidirectional streams prior to reading the stream type.</t> <t>ImplementationsMAY<bcp14>MAY</bcp14> send stream types before knowing whether the peer supports them. However, stream types that could modify the state or semantics of existing protocol components, including QPACK or other extensions,MUST NOT<bcp14>MUST NOT</bcp14> be sent until the peer is known to support them.</t> <t>A sender can close or reset a unidirectional stream unless otherwise specified. A receiverMUST<bcp14>MUST</bcp14> tolerate unidirectional streams being closed or reset prior to the reception of the unidirectional stream header.</t> <sectionanchor="control-streams" numbered="true" toc="default">anchor='control-streams'> <name>ControlStreams</name>Streams</name><iref item='control stream' primary='true'/> <t>A control stream is indicated by a stream type of 0x00. Data on this stream consists of HTTP/3 frames, as defined in <xreftarget="frames" format="default"/>.</t>target='frames'/>.</t> <t>Each sideMUST<bcp14>MUST</bcp14> initiate a single control stream at the beginning of the connection and send itsSETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame as the first frame on this stream. If the first frame of the control stream is any other frame type, thisMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_MISSING_SETTINGS.<xref format='none' target='H3_MISSING_SETTINGS'>H3_MISSING_SETTINGS</xref><iref item='H3_MISSING_SETTINGS'/>. Only one control stream per peer is permitted; receipt of a second stream claiming to be a control streamMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_STREAM_CREATION_ERROR.<xref format='none' target='H3_STREAM_CREATION_ERROR'>H3_STREAM_CREATION_ERROR</xref><iref item='H3_STREAM_CREATION_ERROR'/>. The senderMUST NOT<bcp14>MUST NOT</bcp14> close the control stream, and the receiverMUST NOT<bcp14>MUST NOT</bcp14> request that the sender close the control stream. If either control stream is closed at any point, thisMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_CLOSED_CRITICAL_STREAM.<xref format='none' target='H3_CLOSED_CRITICAL_STREAM'>H3_CLOSED_CRITICAL_STREAM</xref><iref item='H3_CLOSED_CRITICAL_STREAM'/>. Connection errors are described in <xreftarget="errors" format="default"/>.</t>target='errors'/>.</t> <t>Because the contents of the control stream are used to manage the behavior of other streams, endpointsSHOULD<bcp14>SHOULD</bcp14> provide enoughflow controlflow-control credit to keep the peer's control stream from becoming blocked.</t> <t>A pair of unidirectional streams is used rather than a single bidirectional stream. This allows either peer to send data as soon as it is able. Depending on whether 0-RTT is available on the QUIC connection, either client or server might be able to send stream data first.</t> </section> <sectionanchor="push-streams" numbered="true" toc="default">anchor='push-streams'> <name>PushStreams</name>Streams</name><iref item='push stream' primary='true'/> <t>Server push is an optional feature introduced in HTTP/2 that allows a server to initiate a response before a request has been made. See <xreftarget="server-push" format="default"/>target='server-push'/> for more details.</t> <t>A push stream is indicated by a stream type of 0x01, followed by thePush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> of the promise that it fulfills, encoded as a variable-length integer. The remaining data on this stream consists of HTTP/3 frames, as defined in <xreftarget="frames" format="default"/>,target='frames'/>, and fulfills a promised server push by zero or more interim HTTP responses followed by a single final HTTP response, as defined in <xreftarget="request-response" format="default"/>.target='request-response'/>. Server push andPushpush IDs are described in <xreftarget="server-push" format="default"/>.</t>target='server-push'/>.</t> <t>Only servers can push; if a server receives a client-initiated push stream, thisMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_STREAM_CREATION_ERROR; see<xreftarget="errors" format="default"/>.</t> <figure anchor="fig-push-stream-header">format='none' target='H3_STREAM_CREATION_ERROR'>H3_STREAM_CREATION_ERROR</xref><iref item='H3_STREAM_CREATION_ERROR'/>.</t> <figure> <name>Push Stream Header</name> <artworktype="drawing" name="" align="left" alt=""><![CDATA[type='ascii-art'><![CDATA[ Push Stream Header { Stream Type (i) = 0x01, Push ID (i), } ]]></artwork> </figure> <t>A client <bcp14>SHOULD NOT</bcp14> abort reading on a push stream prior to reading the push stream header, as this could lead to disagreement between client and server on which push IDs have already been consumed.</t> <t>EachPush ID MUST<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> <bcp14>MUST</bcp14> only be used once in a push stream header. If a client detects that a push stream header includes aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> that was used in another push stream header, the clientMUST<bcp14>MUST</bcp14> treat this as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_ID_ERROR; see<xreftarget="errors" format="default"/>.</t>format='none' target='H3_ID_ERROR'>H3_ID_ERROR</xref><iref item='H3_ID_ERROR'/>.</t> </section> <sectionanchor="stream-grease" numbered="true" toc="default">anchor='stream-grease'> <name>Reserved Stream Types</name> <t>Stream types of the format <tt>0x1f * N + 0x21</tt> for non-negative integer values ofN<tt>N</tt> are reserved to exercise the requirement that unknown types be ignored. These streams have no semantics, and they can be sent when application-layer padding is desired. TheyMAY<bcp14>MAY</bcp14> also be sent on connections where no data is currently being transferred. EndpointsMUST NOT<bcp14>MUST NOT</bcp14> consider these streams to have any meaning upon receipt.</t> <t>The payload and length of the stream are selected in any manner the sending implementation chooses. When sending a reserved stream type, the implementationMAY<bcp14>MAY</bcp14> either terminate the stream cleanly or reset it. When resetting the stream, either theH3_NO_ERROR<xref format='none' target='H3_NO_ERROR'>H3_NO_ERROR</xref><iref item='H3_NO_ERROR'/> error code or a reserved error code (<xreftarget="http-error-codes" format="default"/>) SHOULDtarget='http-error-codes'/>) <bcp14>SHOULD</bcp14> be used.</t> </section> </section> </section> <sectionanchor="http-framing-layer" numbered="true" toc="default">anchor='http-framing-layer'> <name>HTTP Framing Layer</name> <t>HTTP frames are carried on QUIC streams, as described in <xreftarget="stream-mapping" format="default"/>.target='stream-mapping'/>. HTTP/3 defines three stream types:control stream, request stream, and push stream.<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>, <xref format='none' target='request-streams'>request stream</xref><iref item='request stream'/>, and <xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/>. This section describes HTTP/3 frame formats and their permitted stream types; see <xreftarget="stream-frame-mapping" format="default"/>target='stream-frame-mapping'/> for an overview. A comparison between HTTP/2 and HTTP/3 frames is provided in <xreftarget="h2-frames" format="default"/>.</t>target='h2-frames'/>.</t> <tableanchor="stream-frame-mapping" align="center">anchor='stream-frame-mapping'> <name>HTTP/3 Frames and Stream Type Overview</name> <thead> <tr> <thalign="left">Frame</th>align='left'>Frame</th> <thalign="left">Controlalign='left'>Control Stream</th> <thalign="left">Requestalign='left'>Request Stream</th> <thalign="left">Pushalign='left'>Push Stream</th> <thalign="left">Section</th>align='left'>Section</th> </tr> </thead> <tbody> <tr> <tdalign="left">DATA</td>align='left'><xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/></td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left">Yes</td>align='left'>Yes</td> <tdalign="left">Yes</td>align='left'>Yes</td> <tdalign="left"> <xref target="frame-data" format="default"/></td>align='left'><xref target='frame-data'/></td> </tr> <tr> <tdalign="left">HEADERS</td>align='left'><xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/></td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left">Yes</td>align='left'>Yes</td> <tdalign="left">Yes</td>align='left'>Yes</td> <tdalign="left"> <xref target="frame-headers" format="default"/></td>align='left'><xref target='frame-headers'/></td> </tr> <tr> <tdalign="left">CANCEL_PUSH</td>align='left'><xref format='none' target='frame-cancel-push'>CANCEL_PUSH</xref><iref item='CANCEL_PUSH'/></td> <tdalign="left">Yes</td>align='left'>Yes</td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left"> <xref target="frame-cancel-push" format="default"/></td>align='left'><xref target='frame-cancel-push'/></td> </tr> <tr> <tdalign="left">SETTINGS</td>align='left'><xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/></td> <tdalign="left">Yesalign='left'>Yes (1)</td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left"> <xref target="frame-settings" format="default"/></td>align='left'><xref target='frame-settings'/></td> </tr> <tr> <tdalign="left">PUSH_PROMISE</td>align='left'><xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/></td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left">Yes</td>align='left'>Yes</td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left"> <xref target="frame-push-promise" format="default"/></td>align='left'><xref target='frame-push-promise'/></td> </tr> <tr> <tdalign="left">GOAWAY</td>align='left'><xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/></td> <tdalign="left">Yes</td>align='left'>Yes</td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left"> <xref target="frame-goaway" format="default"/></td>align='left'><xref target='frame-goaway'/></td> </tr> <tr> <tdalign="left">MAX_PUSH_ID</td>align='left'><xref format='none' target='frame-max-push-id'>MAX_PUSH_ID</xref><iref item='MAX_PUSH_ID'/></td> <tdalign="left">Yes</td>align='left'>Yes</td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left">No</td>align='left'>No</td> <tdalign="left"> <xref target="frame-max-push-id" format="default"/></td>align='left'><xref target='frame-max-push-id'/></td> </tr> <tr> <tdalign="left">Reserved</td>align='left'>Reserved</td> <tdalign="left">Yes</td>align='left'>Yes</td> <tdalign="left">Yes</td>align='left'>Yes</td> <tdalign="left">Yes</td>align='left'>Yes</td> <tdalign="left"> <xref target="frame-reserved" format="default"/></td>align='left'><xref target='frame-reserved'/></td> </tr> </tbody> </table> <t>TheSETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame can only occur as the first frame of a Control stream; this is indicated in <xreftarget="stream-frame-mapping" format="default"/>target='stream-frame-mapping'/> with a (1). Specific guidance is provided in the relevant section.</t> <t>Note that, unlike QUIC frames, HTTP/3 frames can span multiple packets.</t> <sectionanchor="frame-layout" numbered="true" toc="default">anchor='frame-layout'> <name>Frame Layout</name> <t>All frames have the following format:</t><figure anchor="fig-frame"><figure> <name>HTTP/3 Frame Format</name> <artworktype="drawing" name="" align="left" alt=""><![CDATA[type='ascii-art'><![CDATA[ HTTP/3 Frame Format { Type (i), Length (i), Frame Payload (..), } ]]></artwork> </figure> <t>A frame includes the following fields:</t> <dl><dt> Type: </dt><dt>Type:</dt> <dd> <t>A variable-length integer that identifies the frame type.</t> </dd><dt> Length: </dt><dt>Length:</dt> <dd> <t>A variable-length integer that describes the length in bytes of the Frame Payload.</t> </dd><dt> Frame Payload: </dt><dt>Frame Payload:</dt> <dd> <t>A payload, the semantics of which are determined by the Type field.</t> </dd> </dl> <t>Each frame's payloadMUST<bcp14>MUST</bcp14> contain exactly the fields identified in its description. A frame payload that contains additional bytes after the identified fields or a frame payload that terminates before the end of the identified fieldsMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_ERROR; see<xreftarget="errors" format="default"/>.format='none' target='H3_FRAME_ERROR'>H3_FRAME_ERROR</xref><iref item='H3_FRAME_ERROR'/>. In particular, redundant length encodingsMUST<bcp14>MUST</bcp14> be verified to be self-consistent; see <xreftarget="frame-parsing" format="default"/>.</t>target='frame-parsing'/>.</t> <t>When a stream terminates cleanly, if the last frame on the stream was truncated, thisMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_ERROR; see<xreftarget="errors" format="default"/>.format='none' target='H3_FRAME_ERROR'>H3_FRAME_ERROR</xref><iref item='H3_FRAME_ERROR'/>. Streams that terminate abruptly may be reset at any point in a frame.</t> </section> <sectionanchor="frames" numbered="true" toc="default">anchor='frames'> <name>Frame Definitions</name> <sectionanchor="frame-data" numbered="true" toc="default"> <name>DATA</name>anchor='frame-data'> <name>DATA</name><iref item='DATA' primary='true'/> <t>DATA frames(type=0x0)(type=0x00) convey arbitrary, variable-length sequences of bytes associated with HTTP request or response content.</t> <t>DATA framesMUST<bcp14>MUST</bcp14> be associated with an HTTP request or response. If a DATA frame is received on acontrol stream,<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>, the recipientMUST<bcp14>MUST</bcp14> respond with aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED; see<xreftarget="errors" format="default"/>.</t> <figure anchor="fig-data">format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> <figure> <name>DATA Frame</name> <artworktype="drawing" name="" align="left" alt=""><![CDATA[type='ascii-art'><![CDATA[ DATA Frame { Type (i) =0x0,0x00, Length (i), Data (..), } ]]></artwork> </figure> </section> <sectionanchor="frame-headers" numbered="true" toc="default"> <name>HEADERS</name>anchor='frame-headers'> <name>HEADERS</name><iref item='HEADERS' primary='true'/> <t>The HEADERS frame(type=0x1)(type=0x01) is used to carry an HTTP fieldsection,section that is encoded using QPACK. See <xreftarget="QPACK" format="default"/>target='RFC9204'/> for more details.</t><figure anchor="fig-headers"><figure> <name>HEADERS Frame</name> <artworktype="drawing" name="" align="left" alt=""><![CDATA[type='ascii-art'><![CDATA[ HEADERS Frame { Type (i) =0x1,0x01, Length (i), Encoded Field Section (..), } ]]></artwork> </figure> <t>HEADERS frames can only be sent onrequest<xref format='none' target='request-streams'>request streams</xref><iref item='request stream'/> orpush streams.<xref format='none' target='push-streams'>push streams</xref><iref item='push stream'/>. If a HEADERS frame is received on acontrol stream,<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>, the recipientMUST<bcp14>MUST</bcp14> respond with aconnection error (<xref target="errors" format="default"/>)<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED.</t><xref format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> </section> <sectionanchor="frame-cancel-push" numbered="true" toc="default"> <name>CANCEL_PUSH</name>anchor='frame-cancel-push'> <name>CANCEL_PUSH</name><iref item='CANCEL_PUSH' primary='true'/> <t>The CANCEL_PUSH frame(type=0x3)(type=0x03) is used to request cancellation of a server push prior to thepush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> being received. The CANCEL_PUSH frame identifies a server push byPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> (see <xreftarget="server-push" format="default"/>),target='server-push'/>), encoded as a variable-length integer.</t> <t>When a client sendsCANCEL_PUSH,a CANCEL_PUSH frame, it is indicating that it does not wish to receive the promised resource. The serverSHOULD<bcp14>SHOULD</bcp14> abort sending the resource, but the mechanism to do so depends on the state of the correspondingpush stream.<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/>. If the server has not yet created apush stream,<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/>, it does not create one. If thepush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> is open, the serverSHOULD<bcp14>SHOULD</bcp14> abruptly terminate that stream. If thepush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> has already ended, the serverMAY<bcp14>MAY</bcp14> still abruptly terminate the stream orMAY<bcp14>MAY</bcp14> take no action.</t> <t>A server sends a CANCEL_PUSH frame to indicate that it will not be fulfilling a promisewhichthat was previously sent. The client cannot expect the corresponding promise to be fulfilled, unless it has already received and processed the promised response. Regardless of whether apush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> has been opened, a serverSHOULD<bcp14>SHOULD</bcp14> send a CANCEL_PUSH frame when it determines that promise will not be fulfilled. If a stream has already been opened, the server can abort sending on the stream with an error code ofH3_REQUEST_CANCELLED.</t><xref format='none' target='H3_REQUEST_CANCELLED'>H3_REQUEST_CANCELLED</xref><iref item='H3_REQUEST_CANCELLED'/>.</t> <t>Sending a CANCEL_PUSH frame has no direct effect on the state of existingpush streams.<xref format='none' target='push-streams'>push streams</xref><iref item='push stream'/>. A clientSHOULD NOT<bcp14>SHOULD NOT</bcp14> send a CANCEL_PUSH frame when it has already received a correspondingpush stream.<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/>. Apush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> could arrive after a client has sent a CANCEL_PUSH frame, because a server might not have processed the CANCEL_PUSH. The clientSHOULD<bcp14>SHOULD</bcp14> abort reading the stream with an error code ofH3_REQUEST_CANCELLED.</t><xref format='none' target='H3_REQUEST_CANCELLED'>H3_REQUEST_CANCELLED</xref><iref item='H3_REQUEST_CANCELLED'/>.</t> <t>A CANCEL_PUSH frame is sent on thecontrol stream.<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>. Receiving a CANCEL_PUSH frame on a stream other than thecontrol stream MUST<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/> <bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED.</t> <figure anchor="fig-cancel-push"><xref format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> <figure> <name>CANCEL_PUSH Frame</name> <artworktype="drawing" name="" align="left" alt=""><![CDATA[type='ascii-art'><![CDATA[ CANCEL_PUSH Frame { Type (i) =0x3,0x03, Length (i), Push ID (i), } ]]></artwork> </figure> <t>The CANCEL_PUSH frame carries aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> encoded as a variable-length integer. The Push ID field identifies the server push that is being cancelled; see <xreftarget="server-push" format="default"/>.target='server-push'/>. If a CANCEL_PUSH frame is received that references aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> greater than currently allowed on the connection, thisMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_ID_ERROR.</t><xref format='none' target='H3_ID_ERROR'>H3_ID_ERROR</xref><iref item='H3_ID_ERROR'/>.</t> <t>If the client receives a CANCEL_PUSH frame, that frame might identify aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> that has not yet been mentioned by aPUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frame due to reordering. If a server receives a CANCEL_PUSH frame for aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> that has not yet been mentioned by aPUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frame, thisMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_ID_ERROR.</t><xref format='none' target='H3_ID_ERROR'>H3_ID_ERROR</xref><iref item='H3_ID_ERROR'/>.</t> </section> <sectionanchor="frame-settings" numbered="true" toc="default"> <name>SETTINGS</name>anchor='frame-settings'> <name>SETTINGS</name><iref item='SETTINGS' primary='true'/> <t>The SETTINGS frame(type=0x4)(type=0x04) conveys configuration parameters that affect how endpoints communicate, such as preferences and constraints on peer behavior. Individually, a SETTINGS parameter can also be referred to as a "setting"; the identifier and value of each setting parameter can be referred to as a "setting identifier" and a "setting value".</t> <t>SETTINGS frames always apply to an entire HTTP/3 connection, never a single stream. A SETTINGS frameMUST<bcp14>MUST</bcp14> be sent as the first frame of eachcontrol stream<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/> (see <xreftarget="control-streams" format="default"/>)target='control-streams'/>) by each peer, andMUST NOTit <bcp14>MUST NOT</bcp14> be sent subsequently. If an endpoint receives a second SETTINGS frame on thecontrol stream,<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>, the endpointMUST<bcp14>MUST</bcp14> respond with aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED.</t><xref format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> <t>SETTINGS framesMUST NOT<bcp14>MUST NOT</bcp14> be sent on any stream other than thecontrol stream.<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>. If an endpoint receives a SETTINGS frame on a different stream, the endpointMUST<bcp14>MUST</bcp14> respond with aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED.</t><xref format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> <t>SETTINGS parameters are not negotiated; they describe characteristics of the sending peer that can be used by the receiving peer. However, a negotiation can be implied by the use ofSETTINGS -SETTINGS: each peer uses SETTINGS to advertise a set of supported values. The definition of the setting would describe how each peer combines the two sets to conclude which choice will be used. SETTINGS does not provide a mechanism to identify when the choice takes effect.</t> <t>Different values for the same parameter can be advertised by each peer. For example, a client might be willing to consume a very large response field section, while servers are more cautious about request size.</t> <t>The same setting identifierMUST NOT<bcp14>MUST NOT</bcp14> occur more than once in the SETTINGS frame. A receiverMAY<bcp14>MAY</bcp14> treat the presence of duplicate setting identifiers as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_SETTINGS_ERROR.</t><xref format='none' target='H3_SETTINGS_ERROR'>H3_SETTINGS_ERROR</xref><iref item='H3_SETTINGS_ERROR'/>.</t> <t>The payload of a SETTINGS frame consists of zero or more parameters. Each parameter consists of a setting identifier and a value, both encoded as QUIC variable-length integers.</t><figure anchor="fig-ext-settings"><figure> <name>SETTINGS Frame</name> <artworktype="drawing" name="" align="left" alt=""><![CDATA[type='ascii-art'><![CDATA[ Setting { Identifier (i), Value (i), } SETTINGS Frame { Type (i) =0x4,0x04, Length (i), Setting (..) ..., } ]]></artwork> </figure> <t>An implementationMUST<bcp14>MUST</bcp14> ignore any parameter with an identifier it does not understand.</t> <sectionanchor="settings-parameters" numbered="true" toc="default">anchor='settings-parameters'> <name>Defined SETTINGS Parameters</name> <t>The following settings are defined in HTTP/3:</t> <dl><dt> SETTINGS_MAX_FIELD_SECTION_SIZE (0x6): </dt><dt>SETTINGS_MAX_FIELD_SECTION_SIZE (0x06)<iref item='SETTINGS_MAX_FIELD_SECTION_SIZE'/>:</dt> <dd><t>The<t anchor='SETTINGS_MAX_FIELD_SECTION_SIZE'>The default value is unlimited. See <xreftarget="header-size-constraints" format="default"/>target='header-size-constraints'/> for usage.</t> </dd> </dl> <t>Setting identifiers of the format <tt>0x1f * N + 0x21</tt> for non-negative integer values ofN<tt>N</tt> are reserved to exercise the requirement that unknown identifiers be ignored. Such settings have no defined meaning. EndpointsSHOULD<bcp14>SHOULD</bcp14> include at least one such setting in their SETTINGS frame. EndpointsMUST NOT<bcp14>MUST NOT</bcp14> consider such settings to have any meaning upon receipt.</t> <t>Because the setting has no defined meaning, the value of the setting can be any value the implementation selects.</t> <t>Setting identifierswhichthat were defined in <xreftarget="HTTP2" format="default"/>target='RFC9113'/> where there is no corresponding HTTP/3 setting have also been reserved (<xreftarget="iana-settings" format="default"/>).target='iana-settings'/>). These reserved settingsMUST NOT<bcp14>MUST NOT</bcp14> be sent, and their receiptMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_SETTINGS_ERROR.</t><xref format='none' target='H3_SETTINGS_ERROR'>H3_SETTINGS_ERROR</xref><iref item='H3_SETTINGS_ERROR'/>.</t> <t>Additional settings can be defined by extensions to HTTP/3; see <xreftarget="extensions" format="default"/>target='extensions'/> for more details.</t> </section> <sectionanchor="settings-initialization" numbered="true" toc="default">anchor='settings-initialization'> <name>Initialization</name> <t>An HTTP implementationMUST NOT<bcp14>MUST NOT</bcp14> send frames or requests that would be invalid based on its current understanding of the peer's settings.</t> <t>All settings begin at an initial value. Each endpointSHOULD<bcp14>SHOULD</bcp14> use these initial values to send messages before the peer's SETTINGS frame has arrived, as packets carrying the settings can be lost or delayed. When the SETTINGS frame arrives, any settings are changed to their new values.</t> <t>This removes the need to wait for the SETTINGS frame before sending messages. EndpointsMUST NOT<bcp14>MUST NOT</bcp14> require any data to be received from the peer prior to sending the SETTINGS frame; settingsMUST<bcp14>MUST</bcp14> be sent as soon as the transport is ready to send data.</t> <t>For servers, the initial value of each client setting is the default value.</t> <t>For clients using a 1-RTT QUIC connection, the initial value of each server setting is the default value. 1-RTT keys will always become available prior to the packet containing SETTINGS being processed by QUIC, even if the server sends SETTINGS immediately. ClientsSHOULD NOT<bcp14>SHOULD NOT</bcp14> wait indefinitely for SETTINGS to arrive before sending requests, butSHOULDthey <bcp14>SHOULD</bcp14> process received datagrams in order to increase the likelihood of processing SETTINGS before sending the first request.</t> <t>When a 0-RTT QUIC connection is being used, the initial value of each server setting is the value used in the previous session. ClientsSHOULD<bcp14>SHOULD</bcp14> store the settings the server provided in the HTTP/3 connection where resumption information was provided, butMAYthey <bcp14>MAY</bcp14> opt not to store settings in certain cases (e.g., if the session ticket is received before the SETTINGS frame). A clientMUST<bcp14>MUST</bcp14> comply with stored settings -- or defaultvalues,values if no values are stored -- when attempting 0-RTT. Once a server has provided new settings, clientsMUST<bcp14>MUST</bcp14> comply with those values.</t> <t>A server can remember the settings that itadvertised,advertised or store an integrity-protected copy of the values in the ticket and recover the information when accepting 0-RTT data. A server uses the HTTP/3 settings values in determining whether to accept 0-RTT data. If the server cannot determine that the settings remembered by a client are compatible with its current settings, itMUST NOT<bcp14>MUST NOT</bcp14> accept 0-RTT data. Remembered settings are compatible if a client complying with those settings would not violate the server's current settings.</t> <t>A serverMAY<bcp14>MAY</bcp14> accept 0-RTT and subsequently provide different settings in its SETTINGS frame. If 0-RTT data is accepted by the server, its SETTINGS frameMUST NOT<bcp14>MUST NOT</bcp14> reduce any limits or alter any values that might be violated by the client with its 0-RTT data. The serverMUST<bcp14>MUST</bcp14> include all settings that differ from their default values. If a server accepts 0-RTT but then sends settings that are not compatible with the previously specified settings, thisMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_SETTINGS_ERROR.<xref format='none' target='H3_SETTINGS_ERROR'>H3_SETTINGS_ERROR</xref><iref item='H3_SETTINGS_ERROR'/>. If a server accepts 0-RTT but then sends a SETTINGS frame that omits a setting value that the client understands (apart from reserved setting identifiers) that was previously specified to have a non-default value, thisMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_SETTINGS_ERROR.</t><xref format='none' target='H3_SETTINGS_ERROR'>H3_SETTINGS_ERROR</xref><iref item='H3_SETTINGS_ERROR'/>.</t> </section> </section> <sectionanchor="frame-push-promise" numbered="true" toc="default"> <name>PUSH_PROMISE</name>anchor='frame-push-promise'> <name>PUSH_PROMISE</name><iref item='PUSH_PROMISE' primary='true'/> <t>The PUSH_PROMISE frame(type=0x5)(type=0x05) is used to carry a promised request header section from server to client on arequest stream, as in HTTP/2.</t> <figure anchor="fig-push-promise"><xref format='none' target='request-streams'>request stream</xref><iref item='request stream'/>.</t> <figure> <name>PUSH_PROMISE Frame</name> <artworktype="drawing" name="" align="left" alt=""><![CDATA[type='ascii-art'><![CDATA[ PUSH_PROMISE Frame { Type (i) =0x5,0x05, Length (i), Push ID (i), Encoded Field Section (..), } ]]></artwork> </figure> <t>The payload consists of:</t> <dl><dt> Push ID: </dt><dt>Push ID:</dt> <dd> <t>A variable-length integer that identifies the server push operation. APush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> is used inpush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> headers (<xreftarget="server-push" format="default"/>)target='server-push'/>) andCANCEL_PUSH frames (<xref target="frame-cancel-push" format="default"/>).</t><xref format='none' target='frame-cancel-push'>CANCEL_PUSH</xref><iref item='CANCEL_PUSH'/> frames.</t> </dd><dt> Encoded<dt>Encoded FieldSection: </dt>Section:</dt> <dd> <t>QPACK-encoded request header fields for the promised response. See <xreftarget="QPACK" format="default"/>target='RFC9204'/> for more details.</t> </dd> </dl> <t>A serverMUST NOT<bcp14>MUST NOT</bcp14> use aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> that is larger than the client has provided in aMAX_PUSH_ID<xref format='none' target='frame-max-push-id'>MAX_PUSH_ID</xref><iref item='MAX_PUSH_ID'/> frame (<xreftarget="frame-max-push-id" format="default"/>).target='frame-max-push-id'/>). A clientMUST<bcp14>MUST</bcp14> treat receipt of a PUSH_PROMISE frame that contains a largerPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> than the client has advertised as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> ofH3_ID_ERROR.</t><xref format='none' target='H3_ID_ERROR'>H3_ID_ERROR</xref><iref item='H3_ID_ERROR'/>.</t> <t>A serverMAY<bcp14>MAY</bcp14> use the samePush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> in multiple PUSH_PROMISE frames. If so, the decompressed request header setsMUST<bcp14>MUST</bcp14> contain the same fields in the same order, and both the name and the value in each fieldMUST<bcp14>MUST</bcp14> be exact matches. ClientsSHOULD<bcp14>SHOULD</bcp14> compare the request header sections for resources promised multiple times. If a client receives aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> that has already been promised and detects a mismatch, itMUST<bcp14>MUST</bcp14> respond with aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_GENERAL_PROTOCOL_ERROR.<xref format='none' target='H3_GENERAL_PROTOCOL_ERROR'>H3_GENERAL_PROTOCOL_ERROR</xref><iref item='H3_GENERAL_PROTOCOL_ERROR'/>. If the decompressed field sections match exactly, the clientSHOULD<bcp14>SHOULD</bcp14> associate the pushed content with each stream on which a PUSH_PROMISE frame was received.</t> <t>Allowing duplicate references to the samePush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> is primarily to reduce duplication caused by concurrent requests. A serverSHOULD<bcp14>SHOULD</bcp14> avoid reusing aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> over a long period. Clients are likely to consume server push responses and not retain them for reuse over time. Clients that see a PUSH_PROMISE frame that uses aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> that they have already consumed and discarded are forced to ignore the promise.</t> <t>If a PUSH_PROMISE frame is received on thecontrol stream,<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>, the clientMUST<bcp14>MUST</bcp14> respond with aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED; see<xreftarget="errors" format="default"/>.</t>format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> <t>A clientMUST NOT<bcp14>MUST NOT</bcp14> send a PUSH_PROMISE frame. A serverMUST<bcp14>MUST</bcp14> treat the receipt of a PUSH_PROMISE frame as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED; see<xreftarget="errors" format="default"/>.</t>format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> <t>See <xreftarget="server-push" format="default"/>target='server-push'/> for a description of the overall server push mechanism.</t> </section> <sectionanchor="frame-goaway" numbered="true" toc="default"> <name>GOAWAY</name>anchor='frame-goaway'> <name>GOAWAY</name><iref item='GOAWAY' primary='true'/> <t>The GOAWAY frame(type=0x7)(type=0x07) is used to initiate graceful shutdown of an HTTP/3 connection by either endpoint. GOAWAY allows an endpoint to stop accepting new requests or pushes while still finishing processing of previously received requests and pushes. This enables administrative actions, like server maintenance. GOAWAY by itself does not close a connection.</t><figure anchor="fig-goaway"><figure> <name>GOAWAY Frame</name> <artworktype="drawing" name="" align="left" alt=""><![CDATA[type='ascii-art'><![CDATA[ GOAWAY Frame { Type (i) =0x7,0x07, Length (i), Stream ID/Push ID(..),(i), } ]]></artwork> </figure> <t>The GOAWAY frame is always sent on thecontrol stream.<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>. In theserver to clientserver-to-client direction, it carries a QUICStreamstream ID for a client-initiated bidirectional stream encoded as a variable-length integer. A clientMUST<bcp14>MUST</bcp14> treat receipt of a GOAWAY frame containing aStreamstream ID of any other type as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_ID_ERROR.</t><xref format='none' target='H3_ID_ERROR'>H3_ID_ERROR</xref><iref item='H3_ID_ERROR'/>.</t> <t>In theclient to serverclient-to-server direction, the GOAWAY frame carries aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> encoded as a variable-length integer.</t> <t>The GOAWAY frame applies to the entire connection, not a specific stream. A clientMUST<bcp14>MUST</bcp14> treat a GOAWAY frame on a stream other than thecontrol stream<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/> as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED; see<xreftarget="errors" format="default"/>.</t>format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> <t>See <xreftarget="connection-shutdown" format="default"/>target='connection-shutdown'/> for more information on the use of the GOAWAY frame.</t> </section> <sectionanchor="frame-max-push-id" numbered="true" toc="default"> <name>MAX_PUSH_ID</name>anchor='frame-max-push-id'> <name>MAX_PUSH_ID</name><iref item='MAX_PUSH_ID' primary='true'/> <t>The MAX_PUSH_ID frame(type=0xd)(type=0x0d) is used by clients to control the number of server pushes that the server can initiate. This sets the maximum value for aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> that the server can use inPUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> andCANCEL_PUSH<xref format='none' target='frame-cancel-push'>CANCEL_PUSH</xref><iref item='CANCEL_PUSH'/> frames. Consequently, this also limits the number ofpush streams<xref format='none' target='push-streams'>push streams</xref><iref item='push stream'/> that the server can initiate in addition to the limit maintained by the QUIC transport.</t> <t>The MAX_PUSH_ID frame is always sent on thecontrol stream.<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>. Receipt of a MAX_PUSH_ID frame on any other streamMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED.</t><xref format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> <t>A serverMUST NOT<bcp14>MUST NOT</bcp14> send a MAX_PUSH_ID frame. A clientMUST<bcp14>MUST</bcp14> treat the receipt of a MAX_PUSH_ID frame as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED.</t><xref format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> <t>The maximumPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> is unset when an HTTP/3 connection is created, meaning that a server cannot push until it receives a MAX_PUSH_ID frame. A client that wishes to manage the number of promised server pushes can increase the maximumPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> by sending MAX_PUSH_ID frames as the server fulfills or cancels server pushes.</t><figure anchor="fig-max-push"><figure> <name>MAX_PUSH_ID Frame</name> <artworktype="drawing" name="" align="left" alt=""><![CDATA[type='ascii-art'><![CDATA[ MAX_PUSH_ID Frame { Type (i) =0xd,0x0d, Length (i), Push ID (i), } ]]></artwork> </figure> <t>The MAX_PUSH_ID frame carries a single variable-length integer that identifies the maximum value for aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> that the server can use; see <xreftarget="server-push" format="default"/>.target='server-push'/>. A MAX_PUSH_ID frame cannot reduce the maximumPush ID;<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/>; receipt of a MAX_PUSH_ID frame that contains a smaller value than previously receivedMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_ID_ERROR.</t><xref format='none' target='H3_ID_ERROR'>H3_ID_ERROR</xref><iref item='H3_ID_ERROR'/>.</t> </section> <sectionanchor="frame-reserved" numbered="true" toc="default">anchor='frame-reserved'> <name>Reserved Frame Types</name> <t>Frame types of the format <tt>0x1f * N + 0x21</tt> for non-negative integer values ofN<tt>N</tt> are reserved to exercise the requirement that unknown types be ignored (<xreftarget="extensions" format="default"/>).target='extensions'/>). These frames have no semantics, andMAYthey <bcp14>MAY</bcp14> be sent on any stream where frames are allowed to be sent. This enables their use for application-layer padding. EndpointsMUST NOT<bcp14>MUST NOT</bcp14> consider these frames to have any meaning upon receipt.</t> <t>The payload and length of the frames are selected in any manner the implementation chooses.</t> <t>Frame types that were used in HTTP/2 where there is no corresponding HTTP/3 frame have also been reserved (<xreftarget="iana-frames" format="default"/>).target='iana-frames'/>). These frame typesMUST NOT<bcp14>MUST NOT</bcp14> be sent, and their receiptMUST<bcp14>MUST</bcp14> be treated as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_FRAME_UNEXPECTED.</t><xref format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>.</t> </section> </section> </section> <sectionanchor="errors" numbered="true" toc="default">anchor='errors'> <name>ErrorHandling</name>Handling</name><iref item='connection error' primary='true'/><iref item='stream error' primary='true'/> <t>When a stream cannot be completed successfully, QUIC allows the application to abruptly terminate (reset) that stream and communicate a reason; see <xrefsection="2.4" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>.section='2.4' sectionFormat='of' target='QUIC-TRANSPORT'/>. This is referred to as a "streamerror."error". An HTTP/3 implementation can decide to close a QUIC stream and communicate the type of error. Wire encodings of error codes are defined in <xreftarget="http-error-codes" format="default"/>.target='http-error-codes'/>. Stream errors are distinct from HTTP status codeswhichthat indicate error conditions. Stream errors indicate that the sender did not transfer or consume the full request or response, while HTTP status codes indicate the result of a request that was successfully received.</t> <t>If an entire connection needs to be terminated, QUIC similarly provides mechanisms to communicate a reason; see <xrefsection="5.3" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>.section='5.3' sectionFormat='of' target='QUIC-TRANSPORT'/>. This is referred to as a "connectionerror."error". Similar to stream errors, an HTTP/3 implementation can terminate a QUIC connection and communicate the reason using an error code from <xreftarget="http-error-codes" format="default"/>.</t>target='http-error-codes'/>.</t> <t>Although the reasons for closing streams and connections are called"errors,""errors", these actions do not necessarily indicate a problem with the connection or either implementation. For example, a stream can be reset if the requested resource is no longer needed.</t> <t>An endpointMAY<bcp14>MAY</bcp14> choose to treat a stream error as a connection error under certain circumstances, closing the entire connection in response to a condition on a single stream. Implementations need to consider the impact on outstanding requests before making this choice.</t> <t>Because new error codes can be defined without negotiation (see <xreftarget="extensions" format="default"/>),target='extensions'/>), use of an error code in an unexpected context or receipt of an unknown error codeMUST<bcp14>MUST</bcp14> be treated as equivalent toH3_NO_ERROR.<xref format='none' target='H3_NO_ERROR'>H3_NO_ERROR</xref><iref item='H3_NO_ERROR'/>. However, closing a stream can have other effects regardless of the error code; for example, see <xreftarget="request-response" format="default"/>.</t>target='request-response'/>.</t> <sectionanchor="http-error-codes" numbered="true" toc="default">anchor='http-error-codes'> <name>HTTP/3 Error Codes</name> <t>The following error codes are defined for use when abruptly terminating streams, aborting reading of streams, or immediately closing HTTP/3 connections.</t> <dl><dt> H3_NO_ERROR (0x100): </dt><dt>H3_NO_ERROR (0x0100)<iref item='H3_NO_ERROR'/>:</dt> <dd><t>No<t anchor='H3_NO_ERROR'>No error. This is used when the connection or stream needs to be closed, but there is no error to signal.</t> </dd><dt> H3_GENERAL_PROTOCOL_ERROR (0x101): </dt><dt>H3_GENERAL_PROTOCOL_ERROR (0x0101)<iref item='H3_GENERAL_PROTOCOL_ERROR'/>:</dt> <dd><t>Peer<t anchor='H3_GENERAL_PROTOCOL_ERROR'>Peer violated protocol requirements in a way that does not match a more specific errorcode,code or endpoint declines to use the more specific error code.</t> </dd><dt> H3_INTERNAL_ERROR (0x102): </dt><dt>H3_INTERNAL_ERROR (0x0102)<iref item='H3_INTERNAL_ERROR'/>:</dt> <dd><t>An<t anchor='H3_INTERNAL_ERROR'>An internal error has occurred in the HTTP stack.</t> </dd><dt> H3_STREAM_CREATION_ERROR (0x103): </dt><dt>H3_STREAM_CREATION_ERROR (0x0103)<iref item='H3_STREAM_CREATION_ERROR'/>:</dt> <dd><t>The<t anchor='H3_STREAM_CREATION_ERROR'>The endpoint detected that its peer created a stream that it will not accept.</t> </dd><dt> H3_CLOSED_CRITICAL_STREAM (0x104): </dt><dt>H3_CLOSED_CRITICAL_STREAM (0x0104)<iref item='H3_CLOSED_CRITICAL_STREAM'/>:</dt> <dd><t>A<t anchor='H3_CLOSED_CRITICAL_STREAM'>A stream required by the HTTP/3 connection was closed or reset.</t> </dd><dt> H3_FRAME_UNEXPECTED (0x105): </dt><dt>H3_FRAME_UNEXPECTED (0x0105)<iref item='H3_FRAME_UNEXPECTED'/>:</dt> <dd><t>A<t anchor='H3_FRAME_UNEXPECTED'>A frame was received that was not permitted in the current state or on the current stream.</t> </dd><dt> H3_FRAME_ERROR (0x106): </dt><dt>H3_FRAME_ERROR (0x0106)<iref item='H3_FRAME_ERROR'/>:</dt> <dd><t>A<t anchor='H3_FRAME_ERROR'>A frame that fails to satisfy layout requirements or with an invalid size was received.</t> </dd><dt> H3_EXCESSIVE_LOAD (0x107): </dt><dt>H3_EXCESSIVE_LOAD (0x0107)<iref item='H3_EXCESSIVE_LOAD'/>:</dt> <dd><t>The<t anchor='H3_EXCESSIVE_LOAD'>The endpoint detected that its peer is exhibiting a behavior that might be generating excessive load.</t> </dd><dt> H3_ID_ERROR (0x108): </dt><dt>H3_ID_ERROR (0x0108)<iref item='H3_ID_ERROR'/>:</dt> <dd><t>A Stream<t anchor='H3_ID_ERROR'>A stream ID orPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> was used incorrectly, such as exceeding a limit, reducing a limit, or being reused.</t> </dd><dt> H3_SETTINGS_ERROR (0x109): </dt><dt>H3_SETTINGS_ERROR (0x0109)<iref item='H3_SETTINGS_ERROR'/>:</dt> <dd><t>An<t anchor='H3_SETTINGS_ERROR'>An endpoint detected an error in the payload of aSETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame.</t> </dd><dt> H3_MISSING_SETTINGS (0x10a): </dt> <dd> <t>No SETTINGS<dt>H3_MISSING_SETTINGS (0x010a)<iref item='H3_MISSING_SETTINGS'/>:</dt> <dd> <t anchor='H3_MISSING_SETTINGS'>No <xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame was received at the beginning of thecontrol stream.</t> </dd> <dt> H3_REQUEST_REJECTED (0x10b): </dt><xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>.</t> </dd> <dt>H3_REQUEST_REJECTED (0x010b)<iref item='H3_REQUEST_REJECTED'/>:</dt> <dd><t>A<t anchor='H3_REQUEST_REJECTED'>A server rejected a request without performing any application processing.</t> </dd><dt> H3_REQUEST_CANCELLED (0x10c): </dt><dt>H3_REQUEST_CANCELLED (0x010c)<iref item='H3_REQUEST_CANCELLED'/>:</dt> <dd><t>The<t anchor='H3_REQUEST_CANCELLED'>The request or its response (including pushed response) is cancelled.</t> </dd><dt> H3_REQUEST_INCOMPLETE (0x10d): </dt><dt>H3_REQUEST_INCOMPLETE (0x010d)<iref item='H3_REQUEST_INCOMPLETE'/>:</dt> <dd><t>The<t anchor='H3_REQUEST_INCOMPLETE'>The client's stream terminated without containing afully-formedfully formed request.</t> </dd><dt> H3_MESSAGE_ERROR (0x10e): </dt><dt>H3_MESSAGE_ERROR (0x010e)<iref item='H3_MESSAGE_ERROR'/>:</dt> <dd><t>An<t anchor='H3_MESSAGE_ERROR'>An HTTP message wasmalformed<xref format='none' target='malformed'>malformed</xref><iref item='malformed'/> and cannot be processed.</t> </dd><dt> H3_CONNECT_ERROR (0x10f): </dt><dt>H3_CONNECT_ERROR (0x010f)<iref item='H3_CONNECT_ERROR'/>:</dt> <dd><t>The<t anchor='H3_CONNECT_ERROR'>The TCP connection established in response to a CONNECT request was reset or abnormally closed.</t> </dd><dt> H3_VERSION_FALLBACK (0x110): </dt><dt>H3_VERSION_FALLBACK (0x0110)<iref item='H3_VERSION_FALLBACK'/>:</dt> <dd><t>The<t anchor='H3_VERSION_FALLBACK'>The requested operation cannot be served over HTTP/3. The peer should retry over HTTP/1.1.</t> </dd> </dl> <t>Error codes of the format <tt>0x1f * N + 0x21</tt> for non-negative integer values ofN<tt>N</tt> are reserved to exercise the requirement that unknown error codes be treated as equivalent toH3_NO_ERROR<xref format='none' target='H3_NO_ERROR'>H3_NO_ERROR</xref><iref item='H3_NO_ERROR'/> (<xreftarget="extensions" format="default"/>).target='extensions'/>). ImplementationsSHOULD<bcp14>SHOULD</bcp14> select an error code from this space with some probability when they would have sentH3_NO_ERROR.</t><xref format='none' target='H3_NO_ERROR'>H3_NO_ERROR</xref><iref item='H3_NO_ERROR'/>.</t> </section> </section> <sectionanchor="extensions" numbered="true" toc="default">anchor='extensions'> <name>Extensions to HTTP/3</name> <t>HTTP/3 permits extension of the protocol. Within the limitations described in this section, protocol extensions can be used to provide additional services or alter any aspect of the protocol. Extensions are effective only within the scope of a single HTTP/3 connection.</t> <t>This applies to the protocol elements defined in this document. This does not affect the existing options for extending HTTP, such as defining new methods, status codes, or fields.</t> <t>Extensions are permitted to use new frame types (<xreftarget="frames" format="default"/>),target='frames'/>), new settings (<xreftarget="settings-parameters" format="default"/>),target='settings-parameters'/>), new error codes (<xreftarget="errors" format="default"/>),target='errors'/>), or new unidirectional stream types (<xreftarget="unidirectional-streams" format="default"/>).target='unidirectional-streams'/>). Registries are established for managing these extension points: frame types (<xreftarget="iana-frames" format="default"/>),target='iana-frames'/>), settings (<xreftarget="iana-settings" format="default"/>),target='iana-settings'/>), error codes (<xreftarget="iana-error-codes" format="default"/>),target='iana-error-codes'/>), and stream types (<xreftarget="iana-stream-types" format="default"/>).</t>target='iana-stream-types'/>).</t> <t>ImplementationsMUST<bcp14>MUST</bcp14> ignore unknown or unsupported values in all extensible protocol elements. ImplementationsMUST<bcp14>MUST</bcp14> discardframes anddata or abort reading on unidirectional streams that have unknown or unsupported types. This means that any of these extension points can be safely used by extensions without prior arrangement or negotiation. However, where a known frame type is required to be in a specific location, such as theSETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame as the first frame of thecontrol stream<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/> (see <xreftarget="control-streams" format="default"/>),target='control-streams'/>), an unknown frame type does not satisfy that requirement andSHOULD<bcp14>SHOULD</bcp14> be treated as an error.</t> <t>Extensions that could change the semantics of existing protocol componentsMUST<bcp14>MUST</bcp14> be negotiated before being used. For example, an extension that changes the layout of theHEADERS<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> frame cannot be used until the peer has given a positive signal that this is acceptable. Coordinating when such a revised layout comes into effect could prove complex. As such, allocating new identifiers for new definitions of existing protocol elements is likely to be more effective.</t> <t>This document does not mandate a specific method for negotiating the use of anextensionextension, but it notes that a setting (<xreftarget="settings-parameters" format="default"/>)target='settings-parameters'/>) could be used for that purpose. If both peers set a value that indicates willingness to use the extension, then the extension can be used. If a setting is used for extension negotiation, the default valueMUST<bcp14>MUST</bcp14> be defined in such a fashion that the extension is disabled if the setting is omitted.</t> </section> <sectionanchor="security-considerations" numbered="true" toc="default">anchor='security-considerations'> <name>Security Considerations</name> <t>The security considerations of HTTP/3 should be comparable to those of HTTP/2 with TLS. However, many of the considerations from <xrefsection="10" sectionFormat="of" target="HTTP2" format="default"/>section='10' sectionFormat='of' target='RFC9113'/> apply to <xreftarget="QUIC-TRANSPORT" format="default"/>target='QUIC-TRANSPORT'/> and are discussed in that document.</t> <sectionanchor="server-authority" numbered="true" toc="default">anchor='server-authority'> <name>Server Authority</name> <t>HTTP/3 relies on the HTTP definition of authority. The security considerations of establishing authority are discussed in <xrefsection="17.1" sectionFormat="of" target="SEMANTICS" format="default"/>.</t>section='17.1' sectionFormat='of' target='RFC9110'/>.</t> </section> <sectionanchor="cross-protocol-attacks" numbered="true" toc="default">anchor='cross-protocol-attacks'> <name>Cross-Protocol Attacks</name> <t>The use of ALPN in the TLS and QUIC handshakes establishes the target application protocol before application-layer bytes are processed. This ensures that endpoints have strong assurances that peers are using the same protocol.</t> <t>This does not guarantee protection from all cross-protocol attacks. <xrefsection="21.5" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>section='21.5' sectionFormat='of' target='QUIC-TRANSPORT'/> describes some ways in which the plaintext of QUIC packets can be used to perform request forgery against endpoints that don't use authenticated transports.</t> </section> <sectionanchor="intermediary-encapsulation-attacks" numbered="true" toc="default"> <name>Intermediary Encapsulationanchor='intermediary-encapsulation-attacks'> <name>Intermediary-Encapsulation Attacks</name> <t>The HTTP/3 field encoding allows the expression of names that are not valid field names in the syntax used by HTTP (<xrefsection="5.1" sectionFormat="of" target="SEMANTICS" format="default"/>).section='5.1' sectionFormat='of' target='RFC9110'/>). Requests or responses containing invalid field namesMUST<bcp14>MUST</bcp14> be treated asmalformed (<xref target="malformed" format="default"/>). An<xref format='none' target='malformed'>malformed</xref><iref item='malformed'/>. Therefore, an intermediarythereforecannot translate an HTTP/3 request or response containing an invalid field name into an HTTP/1.1 message.</t> <t>Similarly, HTTP/3 can transport field values that are not valid. While most values that can be encoded will not alter field parsing, carriage return(CR, ASCII 0xd),(ASCII 0x0d), line feed(LF, ASCII 0xa),(ASCII 0x0a), and thezeronull character(NUL, ASCII 0x0)(ASCII 0x00) might be exploited by an attacker if they are translated verbatim. Any request or response that contains a character not permitted in a field valueMUST<bcp14>MUST</bcp14> be treated asmalformed (<xref target="malformed" format="default"/>).<xref format='none' target='malformed'>malformed</xref><iref item='malformed'/>. Valid characters are defined by the "field-content" ABNF rule in <xrefsection="5.5" sectionFormat="of" target="SEMANTICS" format="default"/>.</t>section='5.5' sectionFormat='of' target='RFC9110'/>.</t> </section> <sectionanchor="cacheability-of-pushed-responses" numbered="true" toc="default">anchor='cacheability-of-pushed-responses'> <name>Cacheability of Pushed Responses</name> <t>Pushed responses do not have an explicit request from the client; the request is provided by the server in thePUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frame.</t> <t>Caching responses that are pushed is possible based on the guidance provided by the origin server in the Cache-Control header field. However, this can cause issues if a single server hosts more than one tenant. For example, a server might offer multiple users each a small portion of its URI space.</t> <t>Where multiple tenants share space on the same server, that serverMUST<bcp14>MUST</bcp14> ensure that tenants are not able to push representations of resources that they do not have authority over. Failure to enforce this would allow a tenant to provide a representation that would be served out of cache, overriding the actual representation that the authoritative tenant provides.</t> <t>Clients are required to reject pushed responses for which an origin server is not authoritative; see <xreftarget="server-push" format="default"/>.</t>target='server-push'/>.</t> </section> <sectionanchor="denial-of-service-considerations" numbered="true" toc="default">anchor='denial-of-service-considerations'> <name>Denial-of-Service Considerations</name> <t>An HTTP/3 connection can demand a greater commitment of resources to operate than an HTTP/1.1 or HTTP/2 connection. The use of field compression and flow control depend on a commitment of resources for storing a greater amount of state. Settings for these features ensure that memory commitments for these features are strictly bounded.</t> <t>The number ofPUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frames is constrained in a similar fashion. A client that accepts server pushSHOULD<bcp14>SHOULD</bcp14> limit the number ofPushpush IDs it issues at a time.</t> <t>Processing capacity cannot be guarded as effectively as state capacity.</t> <t>The ability to send undefined protocol elements that the peer is required to ignore can be abused to cause a peer to expend additional processing time. This might be done by setting multiple undefinedSETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> parameters, unknown frame types, or unknown stream types. Note, however, that some uses are entirely legitimate, such as optional-to-understand extensions and padding to increase resistance to traffic analysis.</t> <t>Compression of field sections also offers some opportunities to waste processing resources; see <xrefsection="7" sectionFormat="of" target="QPACK" format="default"/>section='7' sectionFormat='of' target='RFC9204'/> for more details on potential abuses.</t> <t>All these features -- i.e., server push, unknown protocol elements, field compression -- have legitimate uses. These features become a burden only when they are used unnecessarily or to excess.</t> <t>An endpoint that does not monitor such behavior exposes itself to a risk of denial-of-service attack. ImplementationsSHOULD<bcp14>SHOULD</bcp14> track the use of these features and set limits on their use. An endpointMAY<bcp14>MAY</bcp14> treat activity that is suspicious as aconnection error<xref format='none' target='errors'>connection error</xref><iref item='connection error'/> of typeH3_EXCESSIVE_LOAD (<xref target="errors" format="default"/>),<xref format='none' target='H3_EXCESSIVE_LOAD'>H3_EXCESSIVE_LOAD</xref><iref item='H3_EXCESSIVE_LOAD'/>, but false positives will result in disrupting valid connections and requests.</t> <sectionanchor="limits-on-field-section-size" numbered="true" toc="default">anchor='limits-on-field-section-size'> <name>Limits on Field Section Size</name> <t>A large field section (<xreftarget="request-response" format="default"/>)target='request-response'/>) can cause an implementation to commit a large amount of state. Header fields that are critical for routing can appear toward the end of a header section, which prevents streaming of the header section to its ultimate destination. This ordering and other reasons, such as ensuring cache correctness, mean that an endpoint likely needs to buffer the entire header section. Since there is no hard limit to the size of a field section, some endpoints could be forced to commit a large amount of available memory for header fields.</t> <t>An endpoint can use theSETTINGS_MAX_FIELD_SECTION_SIZE<xref format='none' target='SETTINGS_MAX_FIELD_SECTION_SIZE'>SETTINGS_MAX_FIELD_SECTION_SIZE</xref><iref item='SETTINGS_MAX_FIELD_SECTION_SIZE'/> (<xreftarget="header-size-constraints" format="default"/>)target='header-size-constraints'/>) setting to advise peers of limits that might apply on the size of field sections. This setting is only advisory, so endpointsMAY<bcp14>MAY</bcp14> choose to send field sections that exceed this limit and risk having the request or response being treated asmalformed.<xref format='none' target='malformed'>malformed</xref><iref item='malformed'/>. This setting is specific to an HTTP/3 connection, so any request or response could encounter a hop with a lower, unknown limit. An intermediary can attempt to avoid this problem by passing on values presented by different peers, but they are not obligated to do so.</t> <t>A server that receives a larger field section than it is willing to handle can send an HTTP 431 (Request Header Fields Too Large) status code (<xreftarget="RFC6585" format="default"/>).target='RFC6585'/>). A client can discard responses that it cannot process.</t> </section> <sectionanchor="connect-issues" numbered="true" toc="default">anchor='connect-issues'> <name>CONNECT Issues</name> <t>The CONNECT method can be used to create disproportionate load on a proxy, since stream creation is relatively inexpensive when compared to the creation and maintenance of a TCP connection. Therefore, a proxy that supports CONNECT might be more conservative in the number of simultaneous requests it accepts.</t> <t>A proxy might also maintain some resources for a TCP connection beyond the closing of the stream that carries the CONNECT request, since the outgoing TCP connection remains in the TIME_WAIT state. To account for this, a proxy might delay increasing the QUIC stream limits for some time after a TCP connection terminates.</t> </section> </section> <sectionanchor="use-of-compression" numbered="true" toc="default">anchor='use-of-compression'> <name>Use of Compression</name> <t>Compression can allow an attacker to recover secret data when it is compressed in the same context as data under attacker control. HTTP/3 enables compression of fields (<xreftarget="header-formatting" format="default"/>);target='header-formatting'/>); the following concerns also apply to the use of HTTP compressed content-codings; see <xrefsection="8.4.1" sectionFormat="of" target="SEMANTICS" format="default"/>.</t>section='8.4.1' sectionFormat='of' target='RFC9110'/>.</t> <t>There are demonstrable attacks on compression that exploit the characteristics of the web (e.g., <xreftarget="BREACH" format="default"/>).target='BREACH'/>). The attacker induces multiple requests containing varying plaintext, observing the length of the resulting ciphertext in each, which reveals a shorter length when a guess about the secret is correct.</t> <t>Implementations communicating on a secure channelMUST NOT<bcp14>MUST NOT</bcp14> compress content that includes both confidential and attacker-controlled data unless separate compression contexts are used for each source of data. CompressionMUST NOT<bcp14>MUST NOT</bcp14> be used if the source of data cannot be reliably determined.</t> <t>Further considerations regarding the compression of field sections are described in <xreftarget="QPACK" format="default"/>.</t>target='RFC9204'/>.</t> </section> <sectionanchor="padding-and-traffic-analysis" numbered="true" toc="default">anchor='padding-and-traffic-analysis'> <name>Padding and Traffic Analysis</name> <t>Padding can be used to obscure the exact size of frame content and is provided to mitigate specific attacks within HTTP, for example, attacks where compressed content includes both attacker-controlled plaintext and secret data (e.g., <xreftarget="BREACH" format="default"/>).</t>target='BREACH'/>).</t> <t>Where HTTP/2 employs PADDING frames and Padding fields in other frames to make a connection more resistant to traffic analysis, HTTP/3 can either rely on transport-layer padding or employ the reserved frame and stream types discussed in Sections <xreftarget="frame-reserved" format="default"/>format='counter' target='frame-reserved'/> and <xreftarget="stream-grease" format="default"/>.format='counter' target='stream-grease'/>. These methods of padding produce different results in terms of the granularity of padding, how padding is arranged in relation to the information that is being protected, whether padding is applied in the case of packet loss, and how an implementation might control padding.</t> <t>Reserved stream types can be used to give the appearance of sending traffic even when the connection is idle. Because HTTP traffic often occurs in bursts, apparent traffic can be used to obscure the timing or duration of such bursts, even to the point of appearing to send a constant stream of data. However, as such traffic is still flow controlled by the receiver, a failure to promptly drain such streams and provide additionalflow controlflow-control credit can limit the sender's ability to send real traffic.</t> <t>To mitigate attacks that rely on compression, disabling or limiting compression might be preferable to padding as a countermeasure.</t> <t>Use of padding can result in less protection than might seem immediately obvious. Redundant padding could even be counterproductive. At best, padding only makes it more difficult for an attacker to infer length information by increasing the number of frames an attacker has to observe. Incorrectly implemented padding schemes can be easily defeated. In particular, randomized padding with a predictable distribution provides very little protection; similarly, padding payloads to a fixed size exposes information as payload sizes cross the fixed-sized boundary, which could be possible if an attacker can control plaintext.</t> </section> <sectionanchor="frame-parsing" numbered="true" toc="default">anchor='frame-parsing'> <name>Frame Parsing</name> <t>Several protocol elements contain nested length elements, typically in the form of frames with an explicit length containing variable-length integers. This could pose a security risk to an incautious implementer. An implementationMUST<bcp14>MUST</bcp14> ensure that the length of a frame exactly matches the length of the fields it contains.</t> </section> <sectionanchor="early-data" numbered="true" toc="default">anchor='early-data'> <name>Early Data</name> <t>The use of 0-RTT with HTTP/3 creates an exposure to replay attack. The anti-replay mitigations in <xreftarget="HTTP-REPLAY" format="default"/> MUSTtarget='HTTP-REPLAY'/> <bcp14>MUST</bcp14> be applied when using HTTP/3 with 0-RTT. When applying <xreftarget="HTTP-REPLAY" format="default"/>target='HTTP-REPLAY'/> to HTTP/3, references to the TLS layer refer to the handshake performed within QUIC, while all references to application data refer to the contents of streams.</t> </section> <sectionanchor="migration" numbered="true" toc="default">anchor='migration'> <name>Migration</name> <t>Certain HTTP implementations use the client address for logging or access-control purposes. Since a QUIC client's address might change during a connection (and future versions might support simultaneous use of multiple addresses), such implementations will need to either actively retrieve the client's current address or addresses when they are relevant or explicitly accept that the original address might change.</t> </section> <sectionanchor="privacy-considerations" numbered="true" toc="default">anchor='privacy-considerations'> <name>Privacy Considerations</name> <t>Several characteristics of HTTP/3 provide an observer an opportunity to correlate actions of a single client or server over time. These include the value of settings, the timing of reactions to stimulus, and the handling of any features that are controlled by settings.</t> <t>As far as these create observable differences in behavior, they could be used as a basis for fingerprinting a specific client.</t> <t>HTTP/3's preference for using a single QUIC connection allows correlation of a user's activity on a site. Reusing connections for different origins allows for correlation of activity across those origins.</t> <t>Several features of QUIC solicit immediate responses and can be used by an endpoint to measure latency to their peer; this might have privacy implications in certain scenarios.</t> </section> </section> <sectionanchor="iana-considerations" numbered="true" toc="default">anchor='iana-considerations'> <name>IANA Considerations</name> <t>This document registers a new ALPN protocol ID (<xreftarget="iana-alpn" format="default"/>)target='iana-alpn'/>) and creates new registries that manage the assignment ofcodepointscode points in HTTP/3.</t> <sectionanchor="iana-alpn" numbered="true" toc="default">anchor='iana-alpn'> <name>Registration of HTTP/3 Identification String</name> <t>This document creates a new registration for the identification of HTTP/3 in the"Application Layer"TLS Application-Layer Protocol Negotiation (ALPN) Protocol IDs" registry established in <xreftarget="RFC7301" format="default"/>.</t>target='RFC7301'/>.</t> <t>The "h3" string identifies HTTP/3:</t> <dl><dt> Protocol: </dt><dt>Protocol:</dt> <dd> <t>HTTP/3</t> </dd><dt> Identification Sequence: </dt><dt>Identification Sequence:</dt> <dd> <t>0x68 0x33 ("h3")</t> </dd><dt> Specification: </dt><dt>Specification:</dt> <dd> <t>This document</t> </dd> </dl> </section> <sectionanchor="iana-policy" numbered="true" toc="default">anchor='iana-policy'> <name>New Registries</name> <t>New registries created in this document operate under the QUIC registration policy documented in <xrefsection="22.1" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>.section='22.1' sectionFormat='of' target='QUIC-TRANSPORT'/>. These registries all include the common set of fields listed in <xrefsection="22.1.1" sectionFormat="of" target="QUIC-TRANSPORT" format="default"/>.section='22.1.1' sectionFormat='of' target='QUIC-TRANSPORT'/>. These registries[SHALL be/are]are collected underathe "Hypertext Transfer Protocol version 3(HTTP/3) Parameters"(HTTP/3)" heading.</t> <t>The initial allocations in these registriescreated in this documentare all assigned permanent status and list a change controller of the IETF and a contact of the HTTP working group (ietf-http-wg@w3.org).</t> <sectionanchor="iana-frames" numbered="true" toc="default">anchor='iana-frames'> <name>Frame Types</name> <t>This document establishes a registry for HTTP/3 frame type codes. The "HTTP/3 FrameType"Types" registry governs a 62-bit space. This registry follows the QUIC registry policy; see <xreftarget="iana-policy" format="default"/>.target='iana-policy'/>. Permanent registrations in this registry are assigned using the Specification Required policy (<xreftarget="RFC8126" format="default"/>),target='RFC8126'/>), except for values between 0x00 and 0x3f (in hexadecimal; inclusive), which are assigned using Standards Action or IESG Approval as defined in Sections <xreftarget="RFC8126" section="4.9" sectionFormat="bare" format="default"/>section='4.9' sectionFormat='bare' target='RFC8126'/> and <xreftarget="RFC8126" section="4.10" sectionFormat="bare" format="default"/>section='4.10' sectionFormat='bare' target='RFC8126'/> of <xreftarget="RFC8126" format="default"/>.</t>target='RFC8126'/>.</t> <t>While this registry is separate from the "HTTP/2 Frame Type" registry defined in <xreftarget="HTTP2" format="default"/>,target='RFC9113'/>, it is preferable that the assignments parallel each other where the code spaces overlap. If an entry is present in only one registry, every effortSHOULD<bcp14>SHOULD</bcp14> be made to avoid assigning the corresponding value to an unrelated operation. Expert reviewersMAY<bcp14>MAY</bcp14> reject unrelated registrationswhichthat would conflict with the same value in the corresponding registry.</t> <t>In addition to common fields as described in <xreftarget="iana-policy" format="default"/>,target='iana-policy'/>, permanent registrations in this registryMUST<bcp14>MUST</bcp14> include the following field:</t> <dl><dt> Frame Type: </dt><dt>Frame Type:</dt> <dd> <t>A name or label for the frame type.</t> </dd> </dl> <t>Specifications of frame typesMUST<bcp14>MUST</bcp14> include a description of the frame layout and its semantics, including any parts of the frame that are conditionally present.</t> <t>The entries in <xreftarget="iana-frame-table" format="default"/>target='iana-frame-table'/> are registered by this document.</t> <tableanchor="iana-frame-table" align="center">anchor='iana-frame-table'> <name>Initial HTTP/3 Frame Types</name> <thead> <tr> <thalign="left">Framealign='left'>Frame Type</th> <thalign="center">Value</th>align='center'>Value</th> <thalign="left">Specification</th>align='left'>Specification</th> </tr> </thead> <tbody> <tr> <tdalign="left">DATA</td>align='left'><xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/></td> <tdalign="center">0x0</td>align='center'>0x00</td> <tdalign="left"> <xref target="frame-data" format="default"/></td>align='left'><xref target='frame-data'/></td> </tr> <tr> <tdalign="left">HEADERS</td>align='left'><xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/></td> <tdalign="center">0x1</td>align='center'>0x01</td> <tdalign="left"> <xref target="frame-headers" format="default"/></td>align='left'><xref target='frame-headers'/></td> </tr> <tr> <tdalign="left">Reserved</td>align='left'>Reserved</td> <tdalign="center">0x2</td>align='center'>0x02</td> <tdalign="left">N/A</td>align='left'>This document</td> </tr> <tr> <tdalign="left">CANCEL_PUSH</td>align='left'><xref format='none' target='frame-cancel-push'>CANCEL_PUSH</xref><iref item='CANCEL_PUSH'/></td> <tdalign="center">0x3</td>align='center'>0x03</td> <tdalign="left"> <xref target="frame-cancel-push" format="default"/></td>align='left'><xref target='frame-cancel-push'/></td> </tr> <tr> <tdalign="left">SETTINGS</td>align='left'><xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/></td> <tdalign="center">0x4</td>align='center'>0x04</td> <tdalign="left"> <xref target="frame-settings" format="default"/></td>align='left'><xref target='frame-settings'/></td> </tr> <tr> <tdalign="left">PUSH_PROMISE</td>align='left'><xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/></td> <tdalign="center">0x5</td>align='center'>0x05</td> <tdalign="left"> <xref target="frame-push-promise" format="default"/></td>align='left'><xref target='frame-push-promise'/></td> </tr> <tr> <tdalign="left">Reserved</td>align='left'>Reserved</td> <tdalign="center">0x6</td>align='center'>0x06</td> <tdalign="left">N/A</td>align='left'>This document</td> </tr> <tr> <tdalign="left">GOAWAY</td>align='left'><xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/></td> <tdalign="center">0x7</td>align='center'>0x07</td> <tdalign="left"> <xref target="frame-goaway" format="default"/></td>align='left'><xref target='frame-goaway'/></td> </tr> <tr> <tdalign="left">Reserved</td>align='left'>Reserved</td> <tdalign="center">0x8</td>align='center'>0x08</td> <tdalign="left">N/A</td>align='left'>This document</td> </tr> <tr> <tdalign="left">Reserved</td>align='left'>Reserved</td> <tdalign="center">0x9</td>align='center'>0x09</td> <tdalign="left">N/A</td>align='left'>This document</td> </tr> <tr> <tdalign="left">MAX_PUSH_ID</td>align='left'><xref format='none' target='frame-max-push-id'>MAX_PUSH_ID</xref><iref item='MAX_PUSH_ID'/></td> <tdalign="center">0xd</td>align='center'>0x0d</td> <tdalign="left"> <xref target="frame-max-push-id" format="default"/></td>align='left'><xref target='frame-max-push-id'/></td> </tr> </tbody> </table> <t>Each code of the format <tt>0x1f * N + 0x21</tt> for non-negative integer values ofN<tt>N</tt> (that is, 0x21, 0x40, ..., through 0x3ffffffffffffffe)MUST NOT<bcp14>MUST NOT</bcp14> be assigned by IANA andMUST NOT<bcp14>MUST NOT</bcp14> appear in the listing of assigned values.</t> </section> <sectionanchor="iana-settings" numbered="true" toc="default">anchor='iana-settings'> <name>Settings Parameters</name> <t>This document establishes a registry for HTTP/3 settings. The "HTTP/3 Settings" registry governs a 62-bit space. This registry follows the QUIC registry policy; see <xreftarget="iana-policy" format="default"/>.target='iana-policy'/>. Permanent registrations in this registry are assigned using the Specification Required policy (<xreftarget="RFC8126" format="default"/>),target='RFC8126'/>), except for values between 0x00 and 0x3f (in hexadecimal; inclusive), which are assigned using Standards Action or IESG Approval as defined in Sections <xreftarget="RFC8126" section="4.9" sectionFormat="bare" format="default"/>section='4.9' sectionFormat='bare' target='RFC8126'/> and <xreftarget="RFC8126" section="4.10" sectionFormat="bare" format="default"/>section='4.10' sectionFormat='bare' target='RFC8126'/> of <xreftarget="RFC8126" format="default"/>.</t>target='RFC8126'/>.</t> <t>While this registry is separate from the "HTTP/2 Settings" registry defined in <xreftarget="HTTP2" format="default"/>,target='RFC9113'/>, it is preferable that the assignments parallel each other. If an entry is present in only one registry, every effortSHOULD<bcp14>SHOULD</bcp14> be made to avoid assigning the corresponding value to an unrelated operation. Expert reviewersMAY<bcp14>MAY</bcp14> reject unrelated registrationswhichthat would conflict with the same value in the corresponding registry.</t> <t>In addition to common fields as described in <xreftarget="iana-policy" format="default"/>,target='iana-policy'/>, permanent registrations in this registryMUST<bcp14>MUST</bcp14> include the following fields:</t> <dl><dt> Setting Name: </dt><dt>Setting Name:</dt> <dd> <t>A symbolic name for the setting. Specifying a setting name is optional.</t> </dd><dt> Default: </dt><dt>Default:</dt> <dd> <t>The value of the setting unless otherwise indicated. A defaultSHOULD<bcp14>SHOULD</bcp14> be the most restrictive possible value.</t> </dd> </dl> <t>The entries in <xreftarget="iana-setting-table" format="default"/>target='iana-setting-table'/> are registered by this document.</t> <tableanchor="iana-setting-table" align="center">anchor='iana-setting-table'> <name>Initial HTTP/3 Settings</name> <thead> <tr> <thalign="left">Settingalign='left'>Setting Name</th> <thalign="center">Value</th>align='center'>Value</th> <thalign="left">Specification</th>align='left'>Specification</th> <thalign="left">Default</th>align='left'>Default</th> </tr> </thead> <tbody> <tr> <tdalign="left">Reserved</td>align='left'>Reserved</td> <tdalign="center">0x0</td>align='center'>0x00</td> <tdalign="left">N/A</td>align='left'>This document</td> <tdalign="left">N/A</td>align='left'>N/A</td> </tr> <tr> <tdalign="left">Reserved</td>align='left'>Reserved</td> <tdalign="center">0x2</td>align='center'>0x02</td> <tdalign="left">N/A</td>align='left'>This document</td> <tdalign="left">N/A</td>align='left'>N/A</td> </tr> <tr> <tdalign="left">Reserved</td>align='left'>Reserved</td> <tdalign="center">0x3</td>align='center'>0x03</td> <tdalign="left">N/A</td>align='left'>This document</td> <tdalign="left">N/A</td>align='left'>N/A</td> </tr> <tr> <tdalign="left">Reserved</td>align='left'>Reserved</td> <tdalign="center">0x4</td>align='center'>0x04</td> <tdalign="left">N/A</td>align='left'>This document</td> <tdalign="left">N/A</td>align='left'>N/A</td> </tr> <tr> <tdalign="left">Reserved</td>align='left'>Reserved</td> <tdalign="center">0x5</td>align='center'>0x05</td> <tdalign="left">N/A</td>align='left'>This document</td> <tdalign="left">N/A</td>align='left'>N/A</td> </tr> <tr> <tdalign="left">MAX_FIELD_SECTION_SIZE</td>align='left'>MAX_FIELD_SECTION_SIZE</td> <tdalign="center">0x6</td>align='center'>0x06</td> <tdalign="left"> <xref target="settings-parameters" format="default"/></td>align='left'><xref target='settings-parameters'/></td> <tdalign="left">Unlimited</td>align='left'>Unlimited</td> </tr> </tbody> </table> <t>For formatting reasons, setting names can be abbreviated by removing the 'SETTINGS_' prefix.</t> <t>Each code of the format <tt>0x1f * N + 0x21</tt> for non-negative integer values ofN<tt>N</tt> (that is, 0x21, 0x40, ..., through 0x3ffffffffffffffe)MUST NOT<bcp14>MUST NOT</bcp14> be assigned by IANA andMUST NOT<bcp14>MUST NOT</bcp14> appear in the listing of assigned values.</t> </section> <sectionanchor="iana-error-codes" numbered="true" toc="default">anchor='iana-error-codes'> <name>Error Codes</name> <t>This document establishes a registry for HTTP/3 error codes. The "HTTP/3 ErrorCode"Codes" registry manages a 62-bit space. This registry follows the QUIC registry policy; see <xreftarget="iana-policy" format="default"/>.target='iana-policy'/>. Permanent registrations in this registry are assigned using the Specification Required policy (<xreftarget="RFC8126" format="default"/>),target='RFC8126'/>), except for values between 0x00 and 0x3f (in hexadecimal; inclusive), which are assigned using Standards Action or IESG Approval as defined in Sections <xreftarget="RFC8126" section="4.9" sectionFormat="bare" format="default"/>section='4.9' sectionFormat='bare' target='RFC8126'/> and <xreftarget="RFC8126" section="4.10" sectionFormat="bare" format="default"/>section='4.10' sectionFormat='bare' target='RFC8126'/> of <xreftarget="RFC8126" format="default"/>.</t>target='RFC8126'/>.</t> <t>Registrations for error codes are required to include a description of the error code. An expert reviewer is advised to examine new registrations for possible duplication with existing error codes. Use of existing registrations is to be encouraged, but not mandated. Use of values that are registered in the "HTTP/2 Error Code" registry is discouraged, and expert reviewersMAY<bcp14>MAY</bcp14> reject such registrations.</t> <t>In addition to common fields as described in <xreftarget="iana-policy" format="default"/>,target='iana-policy'/>, this registry includes two additional fields. Permanent registrations in this registryMUST<bcp14>MUST</bcp14> include the following field:</t> <dl><dt> Name: </dt><dt>Name:</dt> <dd> <t>A name for the error code.</t> </dd><dt> Description: </dt><dt>Description:</dt> <dd> <t>A brief description of the error code semantics.</t> </dd> </dl> <t>The entries in <xreftarget="iana-error-table" format="default"/>target='iana-error-table'/> are registered by this document. These error codes were selected from the range that operates on a Specification Required policy to avoid collisions with HTTP/2 error codes.</t> <tableanchor="iana-error-table" align="center">anchor='iana-error-table'> <name>Initial HTTP/3 Error Codes</name> <thead> <tr> <thalign="left">Name</th>align='left'>Name</th> <thalign="left">Value</th>align='left'>Value</th> <thalign="left">Description</th>align='left'>Description</th> <thalign="left">Specification</th>align='left'>Specification</th> </tr> </thead> <tbody> <tr> <tdalign="left">H3_NO_ERROR</td>align='left'><xref format='none' target='H3_NO_ERROR'>H3_NO_ERROR</xref><iref item='H3_NO_ERROR'/></td> <tdalign="left">0x100</td>align='left'>0x0100</td> <tdalign="left">Noalign='left'>No error</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_GENERAL_PROTOCOL_ERROR</td>align='left'><xref format='none' target='H3_GENERAL_PROTOCOL_ERROR'>H3_GENERAL_PROTOCOL_ERROR</xref><iref item='H3_GENERAL_PROTOCOL_ERROR'/></td> <tdalign="left">0x101</td>align='left'>0x0101</td> <tdalign="left">Generalalign='left'>General protocol error</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_INTERNAL_ERROR</td>align='left'><xref format='none' target='H3_INTERNAL_ERROR'>H3_INTERNAL_ERROR</xref><iref item='H3_INTERNAL_ERROR'/></td> <tdalign="left">0x102</td>align='left'>0x0102</td> <tdalign="left">Internalalign='left'>Internal error</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_STREAM_CREATION_ERROR</td>align='left'><xref format='none' target='H3_STREAM_CREATION_ERROR'>H3_STREAM_CREATION_ERROR</xref><iref item='H3_STREAM_CREATION_ERROR'/></td> <tdalign="left">0x103</td>align='left'>0x0103</td> <tdalign="left">Streamalign='left'>Stream creation error</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_CLOSED_CRITICAL_STREAM</td>align='left'><xref format='none' target='H3_CLOSED_CRITICAL_STREAM'>H3_CLOSED_CRITICAL_STREAM</xref><iref item='H3_CLOSED_CRITICAL_STREAM'/></td> <tdalign="left">0x104</td>align='left'>0x0104</td> <tdalign="left">Criticalalign='left'>Critical stream was closed</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_FRAME_UNEXPECTED</td>align='left'><xref format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/></td> <tdalign="left">0x105</td>align='left'>0x0105</td> <tdalign="left">Framealign='left'>Frame not permitted in the current state</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_FRAME_ERROR</td>align='left'><xref format='none' target='H3_FRAME_ERROR'>H3_FRAME_ERROR</xref><iref item='H3_FRAME_ERROR'/></td> <tdalign="left">0x106</td>align='left'>0x0106</td> <tdalign="left">Framealign='left'>Frame violated layout or size rules</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_EXCESSIVE_LOAD</td>align='left'><xref format='none' target='H3_EXCESSIVE_LOAD'>H3_EXCESSIVE_LOAD</xref><iref item='H3_EXCESSIVE_LOAD'/></td> <tdalign="left">0x107</td>align='left'>0x0107</td> <tdalign="left">Peeralign='left'>Peer generating excessive load</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_ID_ERROR</td>align='left'><xref format='none' target='H3_ID_ERROR'>H3_ID_ERROR</xref><iref item='H3_ID_ERROR'/></td> <tdalign="left">0x108</td>align='left'>0x0108</td> <tdalign="left">Analign='left'>An identifier was used incorrectly</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_SETTINGS_ERROR</td> <td align="left">0x109</td> <td align="left">SETTINGSalign='left'><xref format='none' target='H3_SETTINGS_ERROR'>H3_SETTINGS_ERROR</xref><iref item='H3_SETTINGS_ERROR'/></td> <td align='left'>0x0109</td> <td align='left'><xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame contained invalid values</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_MISSING_SETTINGS</td> <td align="left">0x10a</td> <td align="left">No SETTINGSalign='left'><xref format='none' target='H3_MISSING_SETTINGS'>H3_MISSING_SETTINGS</xref><iref item='H3_MISSING_SETTINGS'/></td> <td align='left'>0x010a</td> <td align='left'>No <xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame received</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_REQUEST_REJECTED</td>align='left'><xref format='none' target='H3_REQUEST_REJECTED'>H3_REQUEST_REJECTED</xref><iref item='H3_REQUEST_REJECTED'/></td> <tdalign="left">0x10b</td>align='left'>0x010b</td> <tdalign="left">Requestalign='left'>Request not processed</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_REQUEST_CANCELLED</td>align='left'><xref format='none' target='H3_REQUEST_CANCELLED'>H3_REQUEST_CANCELLED</xref><iref item='H3_REQUEST_CANCELLED'/></td> <tdalign="left">0x10c</td>align='left'>0x010c</td> <tdalign="left">Dataalign='left'>Data no longer needed</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_REQUEST_INCOMPLETE</td>align='left'><xref format='none' target='H3_REQUEST_INCOMPLETE'>H3_REQUEST_INCOMPLETE</xref><iref item='H3_REQUEST_INCOMPLETE'/></td> <tdalign="left">0x10d</td>align='left'>0x010d</td> <tdalign="left">Streamalign='left'>Stream terminated early</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_MESSAGE_ERROR</td>align='left'><xref format='none' target='H3_MESSAGE_ERROR'>H3_MESSAGE_ERROR</xref><iref item='H3_MESSAGE_ERROR'/></td> <tdalign="left">0x10e</td>align='left'>0x010e</td> <tdalign="left">Malformedalign='left'>Malformed message</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_CONNECT_ERROR</td>align='left'><xref format='none' target='H3_CONNECT_ERROR'>H3_CONNECT_ERROR</xref><iref item='H3_CONNECT_ERROR'/></td> <tdalign="left">0x10f</td>align='left'>0x010f</td> <tdalign="left">TCPalign='left'>TCP reset or error on CONNECT request</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> <tr> <tdalign="left">H3_VERSION_FALLBACK</td>align='left'><xref format='none' target='H3_VERSION_FALLBACK'>H3_VERSION_FALLBACK</xref><iref item='H3_VERSION_FALLBACK'/></td> <tdalign="left">0x110</td>align='left'>0x0110</td> <tdalign="left">Retryalign='left'>Retry over HTTP/1.1</td> <tdalign="left"> <xref target="http-error-codes" format="default"/></td>align='left'><xref target='http-error-codes'/></td> </tr> </tbody> </table> <t>Each code of the format <tt>0x1f * N + 0x21</tt> for non-negative integer values ofN<tt>N</tt> (that is, 0x21, 0x40, ..., through 0x3ffffffffffffffe)MUST NOT<bcp14>MUST NOT</bcp14> be assigned by IANA andMUST NOT<bcp14>MUST NOT</bcp14> appear in the listing of assigned values.</t> </section> <sectionanchor="iana-stream-types" numbered="true" toc="default">anchor='iana-stream-types'> <name>Stream Types</name> <t>This document establishes a registry for HTTP/3 unidirectional stream types. The "HTTP/3 StreamType"Types" registry governs a 62-bit space. This registry follows the QUIC registry policy; see <xreftarget="iana-policy" format="default"/>.target='iana-policy'/>. Permanent registrations in this registry are assigned using the Specification Required policy (<xreftarget="RFC8126" format="default"/>),target='RFC8126'/>), except for values between 0x00 and 0x3f (in hexadecimal; inclusive), which are assigned using Standards Action or IESG Approval as defined in Sections <xreftarget="RFC8126" section="4.9" sectionFormat="bare" format="default"/>section='4.9' sectionFormat='bare' target='RFC8126'/> and <xreftarget="RFC8126" section="4.10" sectionFormat="bare" format="default"/>section='4.10' sectionFormat='bare' target='RFC8126'/> of <xreftarget="RFC8126" format="default"/>.</t>target='RFC8126'/>.</t> <t>In addition to common fields as described in <xreftarget="iana-policy" format="default"/>,target='iana-policy'/>, permanent registrations in this registryMUST<bcp14>MUST</bcp14> include the following fields:</t> <dl><dt> Stream Type: </dt><dt>Stream Type:</dt> <dd> <t>A name or label for the stream type.</t> </dd><dt> Sender: </dt><dt>Sender:</dt> <dd> <t>Which endpoint on an HTTP/3 connection may initiate a stream of this type. Values are "Client", "Server", or "Both".</t> </dd> </dl> <t>Specifications for permanent registrationsMUST<bcp14>MUST</bcp14> include a description of the stream type, including the layout and semantics of the stream contents.</t> <t>The entries inthe following table<xref target='iana-stream-type-table'/> are registered by this document.</t> <tablealign="center">anchor='iana-stream-type-table'> <name>Initial Stream Types</name> <thead> <tr> <thalign="left">Streamalign='left'>Stream Type</th> <thalign="center">Value</th>align='center'>Value</th> <thalign="left">Specification</th>align='left'>Specification</th> <thalign="left">Sender</th>align='left'>Sender</th> </tr> </thead> <tbody> <tr> <tdalign="left">Controlalign='left'>Control Stream</td> <tdalign="center">0x00</td>align='center'>0x00</td> <tdalign="left"> <xref target="control-streams" format="default"/></td>align='left'><xref target='control-streams'/></td> <tdalign="left">Both</td>align='left'>Both</td> </tr> <tr> <tdalign="left">Pushalign='left'>Push Stream</td> <tdalign="center">0x01</td>align='center'>0x01</td> <tdalign="left"> <xref target="server-push" format="default"/></td>align='left'><xref target='server-push'/></td> <tdalign="left">Server</td>align='left'>Server</td> </tr> </tbody> </table> <t>Each code of the format <tt>0x1f * N + 0x21</tt> for non-negative integer values ofN<tt>N</tt> (that is, 0x21, 0x40, ..., through 0x3ffffffffffffffe)MUST NOT<bcp14>MUST NOT</bcp14> be assigned by IANA andMUST NOT<bcp14>MUST NOT</bcp14> appear in the listing of assigned values.</t> </section> </section> </section> </middle> <back> <displayreference target='RFC9204' to='QPACK'/> <displayreference target='RFC9110' to='HTTP'/> <displayreference target='RFC9111' to='HTTP-CACHING'/> <displayreference target='RFC9112' to='HTTP/1.1'/> <displayreference target='RFC9113' to='HTTP/2'/> <references> <name>References</name> <references> <name>Normative References</name> <referenceanchor="QUIC-TRANSPORT">anchor='RFC9204' target='https://www.rfc-editor.org/info/rfc9204'> <front><title>QUIC: A UDP-Based Multiplexed and Secure Transport</title><title>QPACK: Field Compression for HTTP/3</title> <author fullname='Charles 'Buck' Krasic' initials='C.' surname='Krasic'> <organization>Google, Inc</organization> </author> <author fullname='Mike Bishop' initials='M.' surname='Bishop'> <organization>Akamai Technologies</organization> </author> <authorinitials="J." surname="Iyengar" fullname="Jana Iyengar" role="editor">fullname='Alan Frindell' initials='A.' role='editor' surname='Frindell'> <organization>Facebook</organization> </author> <date month='June' year='2022'/> </front> <seriesInfo name='RFC' value='9204'/> <seriesInfo name='DOI' value='10.17487/RFC9204'/> </reference> <reference anchor='RFC9110' target='https://www.rfc-editor.org/info/rfc9110'> <front> <title>HTTP Semantics</title> <author fullname='Roy T. Fielding' initials='R.' role='editor' surname='Fielding'> <organization>Adobe</organization> </author> <author fullname='Mark Nottingham' initials='M.' role='editor' surname='Nottingham'> <organization>Fastly</organization> </author> <authorinitials="M." surname="Thomson" fullname="Martin Thomson" role="editor"> <organization>Mozilla</organization>fullname='Julian Reschke' initials='J.' role='editor' surname='Reschke'> <organization>greenbytes</organization> </author> <dateyear="2021" month="February" day="02"/>month='June' year='2022'/> </front> <seriesInfoname="Internet-Draft" value="draft-ietf-quic-transport-34"/>name='STD' value='97'/> <seriesInfo name='RFC' value='9110'/> <seriesInfo name='DOI' value='10.17487/RFC9110'/> </reference> <referenceanchor="QPACK">anchor='RFC9111' target='https://www.rfc-editor.org/info/rfc9111'> <front><title>QPACK: Header Compression for HTTP over QUIC</title><title>HTTP Caching</title> <authorinitials="C." surname="Krasic" fullname="Charles 'Buck' Krasic"> <organization>Google, Inc</organization>fullname='Roy T. Fielding' initials='R.' role='editor' surname='Fielding'> <organization>Adobe</organization> </author> <authorinitials="M." surname="Bishop" fullname="Mike Bishop"> <organization>Akamai Technologies</organization>fullname='Mark Nottingham' initials='M.' role='editor' surname='Nottingham'> <organization>Fastly</organization> </author> <authorinitials="A." surname="Frindell" fullname="Alan Frindell" role="editor"> <organization>Facebook</organization>fullname='Julian Reschke' initials='J.' role='editor' surname='Reschke'> <organization>greenbytes</organization> </author> <dateyear="2021" month="February" day="02"/>month='June' year='2022'/> </front> <seriesInfoname="Internet-Draft" value="draft-ietf-quic-qpack-21"/>name='STD' value='98'/> <seriesInfo name='RFC' value='9111'/> <seriesInfo name='DOI' value='10.17487/RFC9111'/> </reference> <referenceanchor="URI" target="https://www.rfc-editor.org/info/rfc3986">anchor='URI' target='https://www.rfc-editor.org/info/rfc3986'> <front> <title>Uniform Resource Identifier (URI): Generic Syntax</title> <authorinitials="T." surname="Berners-Lee" fullname="T. Berners-Lee">fullname='T. Berners-Lee' initials='T.' surname='Berners-Lee'> <organization/> </author> <authorinitials="R." surname="Fielding" fullname="R. Fielding">fullname='R. Fielding' initials='R.' surname='Fielding'> <organization/> </author> <authorinitials="L." surname="Masinter" fullname="L. Masinter">fullname='L. Masinter' initials='L.' surname='Masinter'> <organization/> </author> <dateyear="2005" month="January"/>month='January' year='2005'/> <abstract> <t>A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK]</t> </abstract> </front> <seriesInfoname="STD" value="66"/>name='STD' value='66'/> <seriesInfoname="RFC" value="3986"/>name='RFC' value='3986'/> <seriesInfoname="DOI" value="10.17487/RFC3986"/>name='DOI' value='10.17487/RFC3986'/> </reference> <referenceanchor="CACHING" target="http://www.ietf.org/internet-drafts/draft-ietf-httpbis-cache-14.txt">anchor='QUIC-TRANSPORT' target='https://www.rfc-editor.org/info/rfc9000'> <front><title>HTTP Caching</title> <author initials="R" surname="Fielding" fullname="Roy Fielding"> <organization/> </author> <author initials="M" surname="Nottingham" fullname="Mark Nottingham"> <organization/> </author> <author initials="J" surname="Reschke" fullname="Julian Reschke"> <organization/> </author> <date month="January" day="12" year="2021"/> <abstract> <t>The Hypertext Transfer Protocol (HTTP) is a stateless application- level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches<title>QUIC: A UDP-Based Multiplexed andthe associated header fields that control cache behavior or indicate cacheable response messages. This document obsoletes RFC 7234.</t> </abstract> </front> <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-cache-14"/> </reference> <reference anchor="SEMANTICS" target="http://www.ietf.org/internet-drafts/draft-ietf-httpbis-semantics-14.txt"> <front> <title>HTTP Semantics</title> <author initials="R" surname="Fielding" fullname="Roy Fielding"> <organization/> </author>Secure Transport</title> <authorinitials="M" surname="Nottingham" fullname="Mark Nottingham">fullname='J. Iyengar' initials='J.' role='editor' surname='Iyengar'> <organization/> </author> <authorinitials="J" surname="Reschke" fullname="Julian Reschke">fullname='M. Thomson' initials='M.' role='editor' surname='Thomson'> <organization/> </author> <datemonth="January" day="12" year="2021"/>month='May' year='2021'/> <abstract><t>The Hypertext Transfer Protocol (HTTP) is a stateless application- level protocol for distributed, collaborative, hypertext information systems. This<t>This documentdescribes the overall architecture of HTTP, establishes common terminology, anddefinesaspects oftheprotocol that are shared by all versions. In this definition arecoreprotocol elements, extensibility mechanisms, andof the"http"QUIC transport protocol. QUIC provides applications with flow-controlled streams for structured communication, low-latency connection establishment, and"https" Uniform Resource Identifier (URI) schemes. This document obsoletes RFC 2818, RFC 7231, RFC 7232, RFC 7233, RFC 7235, RFC 7538, RFC 7615, RFC 7694,network path migration. QUIC includes security measures that ensure confidentiality, integrity, andportionsavailability in a range ofRFC 7230.</t>deployment circumstances. Accompanying documents describe the integration of TLS for key negotiation, loss detection, and an exemplary congestion control algorithm.</t> </abstract> </front> <seriesInfoname="Internet-Draft" value="draft-ietf-httpbis-semantics-14"/>name='RFC' value='9000'/> <seriesInfo name='DOI' value='10.17487/RFC9000'/> </reference> <referenceanchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2119">anchor='RFC2119' target='https://www.rfc-editor.org/info/rfc2119'> <front> <title>Key words for use in RFCs to Indicate Requirement Levels</title> <authorinitials="S." surname="Bradner" fullname="S. Bradner">fullname='S. Bradner' initials='S.' surname='Bradner'> <organization/> </author> <dateyear="1997" month="March"/>month='March' year='1997'/> <abstract> <t>In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t> </abstract> </front> <seriesInfoname="BCP" value="14"/>name='BCP' value='14'/> <seriesInfoname="RFC" value="2119"/>name='RFC' value='2119'/> <seriesInfoname="DOI" value="10.17487/RFC2119"/>name='DOI' value='10.17487/RFC2119'/> </reference> <referenceanchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8174">anchor='RFC8174' target='https://www.rfc-editor.org/info/rfc8174'> <front> <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title> <authorinitials="B." surname="Leiba" fullname="B. Leiba">fullname='B. Leiba' initials='B.' surname='Leiba'> <organization/> </author> <dateyear="2017" month="May"/>month='May' year='2017'/> <abstract> <t>RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t> </abstract> </front> <seriesInfoname="BCP" value="14"/>name='BCP' value='14'/> <seriesInfoname="RFC" value="8174"/>name='RFC' value='8174'/> <seriesInfoname="DOI" value="10.17487/RFC8174"/>name='DOI' value='10.17487/RFC8174'/> </reference> <referenceanchor="RFC7301" target="https://www.rfc-editor.org/info/rfc7301">anchor='RFC7301' target='https://www.rfc-editor.org/info/rfc7301'> <front> <title>Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension</title> <authorinitials="S." surname="Friedl" fullname="S. Friedl">fullname='S. Friedl' initials='S.' surname='Friedl'> <organization/> </author> <authorinitials="A." surname="Popov" fullname="A. Popov">fullname='A. Popov' initials='A.' surname='Popov'> <organization/> </author> <authorinitials="A." surname="Langley" fullname="A. Langley">fullname='A. Langley' initials='A.' surname='Langley'> <organization/> </author> <authorinitials="E." surname="Stephan" fullname="E. Stephan">fullname='E. Stephan' initials='E.' surname='Stephan'> <organization/> </author> <dateyear="2014" month="July"/>month='July' year='2014'/> <abstract> <t>This document describes a Transport Layer Security (TLS) extension for application-layer protocol negotiation within the TLS handshake. For instances in which multiple application protocols are supported on the same TCP or UDP port, this extension allows the application layer to negotiate which protocol will be used within the TLS connection.</t> </abstract> </front> <seriesInfoname="RFC" value="7301"/>name='RFC' value='7301'/> <seriesInfoname="DOI" value="10.17487/RFC7301"/>name='DOI' value='10.17487/RFC7301'/> </reference> <referenceanchor="ALTSVC" target="https://www.rfc-editor.org/info/rfc7838">anchor='ALTSVC' target='https://www.rfc-editor.org/info/rfc7838'> <front> <title>HTTP Alternative Services</title> <authorinitials="M." surname="Nottingham" fullname="M. Nottingham">fullname='M. Nottingham' initials='M.' surname='Nottingham'> <organization/> </author> <authorinitials="P." surname="McManus" fullname="P. McManus">fullname='P. McManus' initials='P.' surname='McManus'> <organization/> </author> <authorinitials="J." surname="Reschke" fullname="J. Reschke">fullname='J. Reschke' initials='J.' surname='Reschke'> <organization/> </author> <dateyear="2016" month="April"/>month='April' year='2016'/> <abstract> <t>This document specifies "Alternative Services" for HTTP, which allow an origin's resources to be authoritatively available at a separate network location, possibly accessed with a different protocol configuration.</t> </abstract> </front> <seriesInfoname="RFC" value="7838"/>name='RFC' value='7838'/> <seriesInfoname="DOI" value="10.17487/RFC7838"/>name='DOI' value='10.17487/RFC7838'/> </reference> <referenceanchor="RFC6066" target="https://www.rfc-editor.org/info/rfc6066">anchor='RFC6066' target='https://www.rfc-editor.org/info/rfc6066'> <front> <title>Transport Layer Security (TLS) Extensions: Extension Definitions</title> <authorinitials="D." surname="Eastlake 3rd" fullname="D.fullname='D. Eastlake3rd">3rd' initials='D.' surname='Eastlake 3rd'> <organization/> </author> <dateyear="2011" month="January"/>month='January' year='2011'/> <abstract> <t>This document provides specifications for existing TLS extensions. It is a companion document for RFC 5246, "The Transport Layer Security (TLS) Protocol Version 1.2". The extensions specified are server_name, max_fragment_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_request. [STANDARDS-TRACK]</t> </abstract> </front> <seriesInfoname="RFC" value="6066"/>name='RFC' value='6066'/> <seriesInfoname="DOI" value="10.17487/RFC6066"/>name='DOI' value='10.17487/RFC6066'/> </reference> <referenceanchor="RFC6265" target="https://www.rfc-editor.org/info/rfc6265">anchor='COOKIES' target='https://www.rfc-editor.org/info/rfc6265'> <front> <title>HTTP State Management Mechanism</title> <authorinitials="A." surname="Barth" fullname="A. Barth">fullname='A. Barth' initials='A.' surname='Barth'> <organization/> </author> <dateyear="2011" month="April"/>month='April' year='2011'/> <abstract> <t>This document defines the HTTP Cookie and Set-Cookie header fields. These header fields can be used by HTTP servers to store state (called cookies) at HTTP user agents, letting the servers maintain a stateful session over the mostly stateless HTTP protocol. Although cookies have many historical infelicities that degrade their security and privacy, the Cookie and Set-Cookie header fields are widely used on the Internet. This document obsoletes RFC 2965. [STANDARDS-TRACK]</t> </abstract> </front> <seriesInfoname="RFC" value="6265"/>name='RFC' value='6265'/> <seriesInfoname="DOI" value="10.17487/RFC6265"/>name='DOI' value='10.17487/RFC6265'/> </reference> <referenceanchor="RFC0793" target="https://www.rfc-editor.org/info/rfc793">anchor='RFC0793' target='https://www.rfc-editor.org/info/rfc793'> <front> <title>Transmission Control Protocol</title> <authorinitials="J." surname="Postel" fullname="J. Postel">fullname='J. Postel' initials='J.' surname='Postel'> <organization/> </author> <dateyear="1981" month="September"/>month='September' year='1981'/> </front> <seriesInfoname="STD" value="7"/>name='STD' value='7'/> <seriesInfoname="RFC" value="793"/>name='RFC' value='793'/> <seriesInfoname="DOI" value="10.17487/RFC0793"/>name='DOI' value='10.17487/RFC0793'/> </reference> <referenceanchor="HTTP-REPLAY" target="https://www.rfc-editor.org/info/rfc8470">anchor='HTTP-REPLAY' target='https://www.rfc-editor.org/info/rfc8470'> <front> <title>Using Early Data in HTTP</title> <authorinitials="M." surname="Thomson" fullname="M. Thomson">fullname='M. Thomson' initials='M.' surname='Thomson'> <organization/> </author> <authorinitials="M." surname="Nottingham" fullname="M. Nottingham">fullname='M. Nottingham' initials='M.' surname='Nottingham'> <organization/> </author> <authorinitials="W." surname="Tarreau" fullname="W. Tarreau">fullname='W. Tarreau' initials='W.' surname='Tarreau'> <organization/> </author> <dateyear="2018" month="September"/>month='September' year='2018'/> <abstract> <t>Using TLS early data creates an exposure to the possibility of a replay attack. This document defines mechanisms that allow clients to communicate with servers about HTTP requests that are sent in early data. Techniques are described that use these mechanisms to mitigate the risk of replay.</t> </abstract> </front> <seriesInfoname="RFC" value="8470"/>name='RFC' value='8470'/> <seriesInfoname="DOI" value="10.17487/RFC8470"/>name='DOI' value='10.17487/RFC8470'/> </reference> <referenceanchor="RFC8126" target="https://www.rfc-editor.org/info/rfc8126">anchor='RFC8126' target='https://www.rfc-editor.org/info/rfc8126'> <front> <title>Guidelines for Writing an IANA Considerations Section in RFCs</title> <authorinitials="M." surname="Cotton" fullname="M. Cotton">fullname='M. Cotton' initials='M.' surname='Cotton'> <organization/> </author> <authorinitials="B." surname="Leiba" fullname="B. Leiba">fullname='B. Leiba' initials='B.' surname='Leiba'> <organization/> </author> <authorinitials="T." surname="Narten" fullname="T. Narten">fullname='T. Narten' initials='T.' surname='Narten'> <organization/> </author> <dateyear="2017" month="June"/>month='June' year='2017'/> <abstract> <t>Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA).</t> <t>To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry.</t> <t>This is the third edition of this document; it obsoletes RFC 5226.</t> </abstract> </front> <seriesInfoname="BCP" value="26"/>name='BCP' value='26'/> <seriesInfoname="RFC" value="8126"/>name='RFC' value='8126'/> <seriesInfoname="DOI" value="10.17487/RFC8126"/>name='DOI' value='10.17487/RFC8126'/> </reference> </references> <references> <name>Informative References</name> <referenceanchor="BREACH" target="http://breachattack.com/resources/BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf">anchor='RFC9112' target='https://www.rfc-editor.org/info/rfc9112'> <front><title>BREACH: Reviving the CRIME Attack</title><title>HTTP/1.1</title> <authorinitials="Y." surname="Gluck"> <organization/>fullname='Roy T. Fielding' initials='R.' role='editor' surname='Fielding'> <organization>Adobe</organization> </author> <authorinitials="N." surname="Harris"> <organization/>fullname='Mark Nottingham' initials='M.' role='editor' surname='Nottingham'> <organization>Fastly</organization> </author> <authorinitials="A." surname="Prado"> <organization/>fullname='Julian Reschke' initials='J.' role='editor' surname='Reschke'> <organization>greenbytes</organization> </author> <dateyear="2013" month="July"/>month='June' year='2022'/> </front> <seriesInfo name='STD' value='99'/> <seriesInfo name='RFC' value='9112'/> <seriesInfo name='DOI' value='10.17487/RFC9112'/> </reference> <referenceanchor="HTTP11" target="http://www.ietf.org/internet-drafts/draft-ietf-httpbis-messaging-14.txt">anchor='RFC9113' target='https://www.rfc-editor.org/info/rfc9113'> <front><title>HTTP/1.1</title> <author initials="R" surname="Fielding" fullname="Roy Fielding"> <organization/> </author><title>HTTP/2</title> <authorinitials="M" surname="Nottingham" fullname="Mark Nottingham"> <organization/>fullname='Martin Thomson' initials='M.' role='editor' surname='Thomson'> <organization>Mozilla</organization> </author> <authorinitials="J" surname="Reschke" fullname="Julian Reschke"> <organization/>fullname='Cory Benfield' initials='C.' role='editor' surname='Benfield'> <organization>Apple Inc.</organization> </author> <datemonth="January" day="12" year="2021"/> <abstract> <t>The Hypertext Transfer Protocol (HTTP) is a stateless application- level protocol for distributed, collaborative, hypertext information systems. This document specifies the HTTP/1.1 message syntax, message parsing, connection management, and related security concerns. This document obsoletes portions of RFC 7230.</t> </abstract>month='June' year='2022'/> </front> <seriesInfoname="Internet-Draft" value="draft-ietf-httpbis-messaging-14"/>name='RFC' value='9113'/> <seriesInfo name='DOI' value='10.17487/RFC9113'/> </reference> <referenceanchor="HTTP2" target="https://www.rfc-editor.org/info/rfc7540">anchor='BREACH' target='http://breachattack.com/resources/BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf'> <front><title>Hypertext Transfer Protocol Version 2 (HTTP/2)</title><title>BREACH: Reviving the CRIME Attack</title> <authorinitials="M." surname="Belshe" fullname="M. Belshe">initials='Y.' surname='Gluck'> <organization/> </author> <authorinitials="R." surname="Peon" fullname="R. Peon">initials='N.' surname='Harris'> <organization/> </author> <authorinitials="M." surname="Thomson" fullname="M. Thomson" role="editor">initials='A.' surname='Prado'> <organization/> </author> <dateyear="2015" month="May"/> <abstract> <t>This specification describes an optimized expression of the semantics of the Hypertext Transfer Protocol (HTTP), referred to as HTTP version 2 (HTTP/2). HTTP/2 enables a more efficient use of network resources and a reduced perception of latency by introducing header field compression and allowing multiple concurrent exchanges on the same connection. It also introduces unsolicited push of representations from servers to clients.</t> <t>This specification is an alternative to, but does not obsolete, the HTTP/1.1 message syntax. HTTP's existing semantics remain unchanged.</t> </abstract>month='July' year='2013'/> </front><seriesInfo name="RFC" value="7540"/> <seriesInfo name="DOI" value="10.17487/RFC7540"/></reference> <referenceanchor="TLS13" target="https://www.rfc-editor.org/info/rfc8446">anchor='TLS' target='https://www.rfc-editor.org/info/rfc8446'> <front> <title>The Transport Layer Security (TLS) Protocol Version 1.3</title> <authorinitials="E." surname="Rescorla" fullname="E. Rescorla">fullname='E. Rescorla' initials='E.' surname='Rescorla'> <organization/> </author> <dateyear="2018" month="August"/>month='August' year='2018'/> <abstract> <t>This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery.</t> <t>This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations.</t> </abstract> </front> <seriesInfoname="RFC" value="8446"/>name='RFC' value='8446'/> <seriesInfoname="DOI" value="10.17487/RFC8446"/>name='DOI' value='10.17487/RFC8446'/> </reference> <referenceanchor="TFO" target="https://www.rfc-editor.org/info/rfc7413">anchor='TFO' target='https://www.rfc-editor.org/info/rfc7413'> <front> <title>TCP Fast Open</title> <authorinitials="Y." surname="Cheng" fullname="Y. Cheng">fullname='Y. Cheng' initials='Y.' surname='Cheng'> <organization/> </author> <authorinitials="J." surname="Chu" fullname="J. Chu">fullname='J. Chu' initials='J.' surname='Chu'> <organization/> </author> <authorinitials="S." surname="Radhakrishnan" fullname="S. Radhakrishnan">fullname='S. Radhakrishnan' initials='S.' surname='Radhakrishnan'> <organization/> </author> <authorinitials="A." surname="Jain" fullname="A. Jain">fullname='A. Jain' initials='A.' surname='Jain'> <organization/> </author> <dateyear="2014" month="December"/>month='December' year='2014'/> <abstract> <t>This document describes an experimental TCP mechanism called TCP Fast Open (TFO). TFO allows data to be carried in the SYN and SYN-ACK packets and consumed by the receiving end during the initial connection handshake, and saves up to one full round-trip time (RTT) compared to the standard TCP, which requires a three-way handshake (3WHS) to complete before data can be exchanged. However, TFO deviates from the standard TCP semantics, since the data in the SYN could be replayed to an application in some rare circumstances. Applications should not use TFO unless they can tolerate this issue, as detailed in the Applicability section.</t> </abstract> </front> <seriesInfoname="RFC" value="7413"/>name='RFC' value='7413'/> <seriesInfoname="DOI" value="10.17487/RFC7413"/>name='DOI' value='10.17487/RFC7413'/> </reference> <referenceanchor="HPACK" target="https://www.rfc-editor.org/info/rfc7541">anchor='HPACK' target='https://www.rfc-editor.org/info/rfc7541'> <front> <title>HPACK: Header Compression for HTTP/2</title> <authorinitials="R." surname="Peon" fullname="R. Peon">fullname='R. Peon' initials='R.' surname='Peon'> <organization/> </author> <authorinitials="H." surname="Ruellan" fullname="H. Ruellan">fullname='H. Ruellan' initials='H.' surname='Ruellan'> <organization/> </author> <dateyear="2015" month="May"/>month='May' year='2015'/> <abstract> <t>This specification defines HPACK, a compression format for efficiently representing HTTP header fields, to be used in HTTP/2.</t> </abstract> </front> <seriesInfoname="RFC" value="7541"/>name='RFC' value='7541'/> <seriesInfoname="DOI" value="10.17487/RFC7541"/>name='DOI' value='10.17487/RFC7541'/> </reference> <referenceanchor="RFC8164" target="https://www.rfc-editor.org/info/rfc8164">anchor='RFC8164' target='https://www.rfc-editor.org/info/rfc8164'> <front> <title>Opportunistic Security for HTTP/2</title> <authorinitials="M." surname="Nottingham" fullname="M. Nottingham">fullname='M. Nottingham' initials='M.' surname='Nottingham'> <organization/> </author> <authorinitials="M." surname="Thomson" fullname="M. Thomson">fullname='M. Thomson' initials='M.' surname='Thomson'> <organization/> </author> <dateyear="2017" month="May"/>month='May' year='2017'/> <abstract> <t>This document describes how "http" URIs can be accessed using Transport Layer Security (TLS) and HTTP/2 to mitigate pervasive monitoring attacks. This mechanism not a replacement for "https" URIs; it is vulnerable to active attacks.</t> </abstract> </front> <seriesInfoname="RFC" value="8164"/>name='RFC' value='8164'/> <seriesInfoname="DOI" value="10.17487/RFC8164"/>name='DOI' value='10.17487/RFC8164'/> </reference> <referenceanchor="DNS-TERMS" target="https://www.rfc-editor.org/info/rfc8499">anchor='DNS-TERMS' target='https://www.rfc-editor.org/info/rfc8499'> <front> <title>DNS Terminology</title> <authorinitials="P." surname="Hoffman" fullname="P. Hoffman">fullname='P. Hoffman' initials='P.' surname='Hoffman'> <organization/> </author> <authorinitials="A." surname="Sullivan" fullname="A. Sullivan">fullname='A. Sullivan' initials='A.' surname='Sullivan'> <organization/> </author> <authorinitials="K." surname="Fujiwara" fullname="K. Fujiwara">fullname='K. Fujiwara' initials='K.' surname='Fujiwara'> <organization/> </author> <dateyear="2019" month="January"/>month='January' year='2019'/> <abstract> <t>The Domain Name System (DNS) is defined in literally dozens of different RFCs. The terminology used by implementers and developers of DNS protocols, and by operators of DNS systems, has sometimes changed in the decades since the DNS was first defined. This document gives current definitions for many of the terms used in the DNS in a single document.</t> <t>This document obsoletes RFC 7719 and updates RFC 2308.</t> </abstract> </front> <seriesInfoname="BCP" value="219"/>name='BCP' value='219'/> <seriesInfoname="RFC" value="8499"/>name='RFC' value='8499'/> <seriesInfoname="DOI" value="10.17487/RFC8499"/>name='DOI' value='10.17487/RFC8499'/> </reference> <referenceanchor="RFC6585" target="https://www.rfc-editor.org/info/rfc6585">anchor='RFC6585' target='https://www.rfc-editor.org/info/rfc6585'> <front> <title>Additional HTTP Status Codes</title> <authorinitials="M." surname="Nottingham" fullname="M. Nottingham">fullname='M. Nottingham' initials='M.' surname='Nottingham'> <organization/> </author> <authorinitials="R." surname="Fielding" fullname="R. Fielding">fullname='R. Fielding' initials='R.' surname='Fielding'> <organization/> </author> <dateyear="2012" month="April"/>month='April' year='2012'/> <abstract> <t>This document specifies additional HyperText Transfer Protocol (HTTP) status codes for a variety of common situations. [STANDARDS-TRACK]</t> </abstract> </front> <seriesInfoname="RFC" value="6585"/>name='RFC' value='6585'/> <seriesInfoname="DOI" value="10.17487/RFC6585"/>name='DOI' value='10.17487/RFC6585'/> </reference> </references> </references> <sectionanchor="h2-considerations" numbered="true" toc="default">anchor='h2-considerations'> <name>Considerations for Transitioning from HTTP/2</name> <t>HTTP/3 is strongly informed by HTTP/2, and it bears many similarities. This section describes the approach taken to design HTTP/3, points out important differences from HTTP/2, and describes how to map HTTP/2 extensions into HTTP/3.</t> <t>HTTP/3 begins from the premise that similarity to HTTP/2 is preferable, but not a hard requirement. HTTP/3 departs from HTTP/2 where QUIC differs from TCP, either to take advantage of QUIC features (like streams) or to accommodate important shortcomings (such as a lack of total ordering).These differences makeWhile HTTP/3 is similar to HTTP/2 in key aspects, such as the relationship of requests and responses tostreams. However,streams, the details of the HTTP/3 design are substantially different from HTTP/2.</t> <t>Some important departures are noted in this section.</t> <sectionanchor="h2-streams" numbered="true" toc="default">anchor='h2-streams'> <name>Streams</name> <t>HTTP/3 permits use of a larger number of streams (2<sup>62</sup>-1) than HTTP/2. The same considerations about exhaustion of stream identifier space apply, though the space is significantly larger such that it is likely that other limits in QUIC are reached first, such as the limit on the connectionflow controlflow-control window.</t> <t>In contrast to HTTP/2, stream concurrency in HTTP/3 is managed by QUIC. QUIC considers a stream closed when all data has been received and sent data has been acknowledged by the peer. HTTP/2 considers a stream closed when the frame containing the END_STREAM bit has been committed to the transport. As a result, the stream for an equivalent exchange could remain "active" for a longer period of time. HTTP/3 servers might choose to permit a larger number of concurrent client-initiated bidirectional streams to achieve equivalent concurrency to HTTP/2, depending on the expected usage patterns.</t> <t>In HTTP/2, only request and response bodies (the frame payload ofDATA<xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frames) are subject to flow control. All HTTP/3 frames are sent on QUIC streams, so all frames on all streams areflow-controlledflow controlled in HTTP/3.</t> <t>Due to the presence of other unidirectional stream types, HTTP/3 does not rely exclusively on the number of concurrent unidirectional streams to control the number of concurrent in-flight pushes. Instead, HTTP/3 clients use theMAX_PUSH_ID<xref format='none' target='frame-max-push-id'>MAX_PUSH_ID</xref><iref item='MAX_PUSH_ID'/> frame to control the number of pushes received from an HTTP/3 server.</t> </section> <sectionanchor="h2-frames" numbered="true" toc="default">anchor='h2-frames'> <name>HTTP Frame Types</name> <t>Many framing concepts from HTTP/2 can be elided on QUIC, because the transport deals with them. Because frames are already on a stream, they can omit the stream number. Because frames do not block multiplexing (QUIC's multiplexing occurs below this layer), the support for variable-maximum-length packets can be removed. Because stream termination is handled by QUIC, an END_STREAM flag is not required. This permits the removal of the Flags field from the generic frame layout.</t> <t>Frame payloads are largely drawn from <xreftarget="HTTP2" format="default"/>.target='RFC9113'/>. However, QUIC includes many features (e.g., flow control) that are also present in HTTP/2. In these cases, the HTTP mapping does not re-implement them. As a result, several HTTP/2 frame types are not required in HTTP/3. Where an HTTP/2-defined frame is no longer used, the frame ID has been reserved in order to maximize portability between HTTP/2 and HTTP/3 implementations. However, even frame types that appear in both mappings do not have identical semantics.</t> <t>Many of the differences arise from the fact that HTTP/2 provides an absolute ordering between frames across all streams, while QUIC provides this guarantee on each stream only. As a result, if a frame type makes assumptions that frames from different streams will still be received in the order sent, HTTP/3 will break them.</t> <t>Some examples of feature adaptations are described below, as well as general guidance to extension frame implementors converting an HTTP/2 extension to HTTP/3.</t> <sectionanchor="h2-diff-priority" numbered="true" toc="default">anchor='h2-diff-priority'> <name>Prioritization Differences</name> <t>HTTP/2 specifies priority assignments in PRIORITY frames and (optionally) inHEADERS<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> frames. HTTP/3 does not provide a means of signaling priority.</t> <t>Notethatthat, while there is no explicit signaling for priority, this does not mean that prioritization is not important for achieving good performance.</t> </section> <sectionanchor="field-compression-differences" numbered="true" toc="default">anchor='field-compression-differences'> <name>Field Compression Differences</name> <t>HPACK was designed with the assumption of in-order delivery. A sequence of encoded field sections must arrive (and be decoded) at an endpoint in the same order in which they were encoded. This ensures that the dynamic state at the two endpoints remains in sync.</t> <t>Because this total ordering is not provided by QUIC, HTTP/3 uses a modified version of HPACK, called QPACK. QPACK uses a single unidirectional stream to make all modifications to the dynamic table, ensuring a total order of updates. All frames that contain encoded fields merely reference the table state at a given time without modifying it.</t> <t><xreftarget="QPACK" format="default"/>target='RFC9204'/> provides additional details.</t> </section> <sectionanchor="flow-control-differences" numbered="true" toc="default"> <name>Flow Controlanchor='flow-control-differences'> <name>Flow-Control Differences</name> <t>HTTP/2 specifies a streamflow controlflow-control mechanism. Although all HTTP/2 frames are delivered on streams, only theDATA<xref format='none' target='frame-data'>DATA</xref><iref item='DATA'/> frame payload is subject to flow control. QUIC provides flow control for stream data and all HTTP/3 frame types defined in this document are sent on streams. Therefore, all frame headers and payload are subject to flow control.</t> </section> <sectionanchor="guidance-for-new-frame-type-definitions" numbered="true" toc="default">anchor='guidance-for-new-frame-type-definitions'> <name>Guidance for New Frame Type Definitions</name> <t>Frame type definitions in HTTP/3 often use the QUIC variable-length integer encoding. In particular,Streamstream IDs use this encoding, which allows for a larger range of possible values than the encoding used in HTTP/2. Some frames in HTTP/3 use an identifier other than aStreamstream ID (e.g.,Pushpush IDs). Redefinition of the encoding of extension frame types might be necessary if the encoding includes aStreamstream ID.</t> <t>Because the Flags field is not present in generic HTTP/3 frames, those frames that depend on the presence of flags need to allocate space for flags as part of their frame payload.</t> <t>Other than these issues, frame type HTTP/2 extensions are typically portable to QUIC simply by replacingStreamstream 0 in HTTP/2 with acontrol stream<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/> in HTTP/3. HTTP/3 extensions will not assume ordering, but would not be harmed by ordering, and are expected to be portable to HTTP/2.</t> </section> <sectionanchor="comparison-between-http2-and-http3-frame-types" numbered="true" toc="default">anchor='comparison-of-http2-and-http3-frame-types'> <name>ComparisonBetweenof HTTP/2 and HTTP/3 Frame Types</name> <dl><dt> DATA (0x0): </dt><dt><xref format='none' target='frame-data'>DATA</xref> (0x00)<iref item='DATA'/>:</dt> <dd> <t>Padding is not defined in HTTP/3 frames. See <xreftarget="frame-data" format="default"/>.</t>target='frame-data'/>.</t> </dd><dt> HEADERS (0x1): </dt><dt><xref format='none' target='frame-headers'>HEADERS</xref> (0x01)<iref item='HEADERS'/>:</dt> <dd> <t>The PRIORITY region ofHEADERS<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/> is not defined in HTTP/3 frames. Padding is not defined in HTTP/3 frames. See <xreftarget="frame-headers" format="default"/>.</t>target='frame-headers'/>.</t> </dd><dt> PRIORITY (0x2): </dt><dt>PRIORITY (0x02):</dt> <dd> <t>As described in <xreftarget="h2-diff-priority" format="default"/>,target='h2-diff-priority'/>, HTTP/3 does not provide a means of signaling priority.</t> </dd><dt> RST_STREAM (0x3): </dt><dt>RST_STREAM (0x03):</dt> <dd> <t>RST_STREAM frames do not exist in HTTP/3, since QUIC provides stream lifecycle management. The same code point is used for theCANCEL_PUSH<xref format='none' target='frame-cancel-push'>CANCEL_PUSH</xref><iref item='CANCEL_PUSH'/> frame (<xreftarget="frame-cancel-push" format="default"/>).</t> </dd> <dt> SETTINGS (0x4): </dt>target='frame-cancel-push'/>).</t> </dd> <dt><xref format='none' target='frame-settings'>SETTINGS</xref> (0x04)<iref item='SETTINGS'/>:</dt> <dd><t>SETTINGS<t><xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frames are sent only at the beginning of the connection. See <xreftarget="frame-settings" format="default"/>target='frame-settings'/> and <xreftarget="h2-settings" format="default"/>.</t>target='h2-settings'/>.</t> </dd><dt> PUSH_PROMISE (0x5): </dt><dt><xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref> (0x05)<iref item='PUSH_PROMISE'/>:</dt> <dd> <t>ThePUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frame does not reference a stream;insteadinstead, thepush stream<xref format='none' target='push-streams'>push stream</xref><iref item='push stream'/> references thePUSH_PROMISE<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frame using aPush ID.<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/>. See <xreftarget="frame-push-promise" format="default"/>.</t>target='frame-push-promise'/>.</t> </dd><dt> PING (0x6): </dt><dt>PING (0x06):</dt> <dd> <t>PING frames do not exist in HTTP/3, as QUIC provides equivalent functionality.</t> </dd><dt> GOAWAY (0x7): </dt><dt><xref format='none' target='frame-goaway'>GOAWAY</xref> (0x07)<iref item='GOAWAY'/>:</dt> <dd><t>GOAWAY<t><xref format='none' target='frame-goaway'>GOAWAY</xref><iref item='GOAWAY'/> does not contain an error code. In theclient to serverclient-to-server direction, it carries aPush ID<xref format='none' target='server-push'>push ID</xref><iref item='push ID'/> instead of aserver initiatedserver-initiated stream ID. See <xreftarget="frame-goaway" format="default"/>.</t>target='frame-goaway'/>.</t> </dd><dt> WINDOW_UPDATE (0x8): </dt><dt>WINDOW_UPDATE (0x08):</dt> <dd> <t>WINDOW_UPDATE frames do not exist in HTTP/3, since QUIC provides flow control.</t> </dd><dt> CONTINUATION (0x9): </dt><dt>CONTINUATION (0x09):</dt> <dd> <t>CONTINUATION frames do not exist in HTTP/3; instead, largerHEADERS/PUSH_PROMISE<xref format='none' target='frame-headers'>HEADERS</xref><iref item='HEADERS'/>/<xref format='none' target='frame-push-promise'>PUSH_PROMISE</xref><iref item='PUSH_PROMISE'/> frames than HTTP/2 are permitted.</t> </dd> </dl> <t>Frame types defined by extensions to HTTP/2 need to be separately registered for HTTP/3 if still applicable. The IDs of frames defined in <xreftarget="HTTP2" format="default"/>target='RFC9113'/> have been reserved for simplicity. Note that the frame type space in HTTP/3 is substantially larger (62 bits versus 8 bits), so many HTTP/3 frame types have no equivalent HTTP/2 code points. See <xreftarget="iana-frames" format="default"/>.</t>target='iana-frames'/>.</t> </section> </section> <sectionanchor="h2-settings" numbered="true" toc="default">anchor='h2-settings'> <name>HTTP/2 SETTINGS Parameters</name> <t>An important difference from HTTP/2 is that settings are sent once, as the first frame of thecontrol stream,<xref format='none' target='control-streams'>control stream</xref><iref item='control stream'/>, and thereafter cannot change. This eliminates many corner cases around synchronization of changes.</t> <t>Some transport-level options that HTTP/2 specifies via theSETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame are superseded by QUIC transport parameters in HTTP/3. The HTTP-level setting that is retained in HTTP/3 has the same value as in HTTP/2. The superseded settings are reserved, and their receipt is an error. See <xreftarget="settings-parameters" format="default"/>target='settings-parameters'/> for discussion of both the retained and reserved values.</t> <t>Below is a listing of how each HTTP/2SETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> parameter is mapped:</t> <dl><dt> SETTINGS_HEADER_TABLE_SIZE (0x1): </dt><dt>SETTINGS_HEADER_TABLE_SIZE (0x01):</dt> <dd> <t>See <xreftarget="QPACK" format="default"/>.</t>target='RFC9204'/>.</t> </dd><dt> SETTINGS_ENABLE_PUSH (0x2): </dt><dt>SETTINGS_ENABLE_PUSH (0x02):</dt> <dd> <t>This is removed in favor of theMAX_PUSH_ID<xref format='none' target='frame-max-push-id'>MAX_PUSH_ID</xref><iref item='MAX_PUSH_ID'/> frame, which provides a more granular control over server push. Specifying a setting with the identifier0x20x02 (corresponding to the SETTINGS_ENABLE_PUSH parameter) in the HTTP/3SETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame is an error.</t> </dd><dt> SETTINGS_MAX_CONCURRENT_STREAMS (0x3): </dt><dt>SETTINGS_MAX_CONCURRENT_STREAMS (0x03):</dt> <dd> <t>QUIC controls the largest openStreamstream ID as part of itsflow controlflow-control logic. Specifying a setting with the identifier0x30x03 (corresponding to the SETTINGS_MAX_CONCURRENT_STREAMS parameter) in the HTTP/3SETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame is an error.</t> </dd><dt> SETTINGS_INITIAL_WINDOW_SIZE (0x4): </dt><dt>SETTINGS_INITIAL_WINDOW_SIZE (0x04):</dt> <dd> <t>QUIC requires both stream and connectionflow controlflow-control window sizes to be specified in the initial transport handshake. Specifying a setting with the identifier0x40x04 (corresponding to the SETTINGS_INITIAL_WINDOW_SIZE parameter) in the HTTP/3SETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame is an error.</t> </dd><dt> SETTINGS_MAX_FRAME_SIZE (0x5): </dt><dt>SETTINGS_MAX_FRAME_SIZE (0x05):</dt> <dd> <t>This setting has no equivalent in HTTP/3. Specifying a setting with the identifier0x50x05 (corresponding to the SETTINGS_MAX_FRAME_SIZE parameter) in the HTTP/3SETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> frame is an error.</t> </dd><dt> SETTINGS_MAX_HEADER_LIST_SIZE (0x6): </dt><dt>SETTINGS_MAX_HEADER_LIST_SIZE (0x06):</dt> <dd> <t>This setting identifier has been renamedSETTINGS_MAX_FIELD_SECTION_SIZE.</t><xref format='none' target='SETTINGS_MAX_FIELD_SECTION_SIZE'>SETTINGS_MAX_FIELD_SECTION_SIZE</xref><iref item='SETTINGS_MAX_FIELD_SECTION_SIZE'/>.</t> </dd> </dl> <t>In HTTP/3, setting values are variable-length integers (6, 14, 30, or 62 bits long) rather than fixed-length 32-bit fields as in HTTP/2. This will often produce a shorter encoding, but can produce a longer encoding for settings that use the full 32-bit space. Settings ported from HTTP/2 might choose to redefine their value to limit it to 30 bits for more efficientencoding,encoding or to make use of the 62-bit space if more than 30 bits are required.</t> <t>Settings need to be defined separately for HTTP/2 and HTTP/3. The IDs of settings defined in <xreftarget="HTTP2" format="default"/>target='RFC9113'/> have been reserved for simplicity. Note that the settings identifier space in HTTP/3 is substantially larger (62 bits versus 16 bits), so many HTTP/3 settings have no equivalent HTTP/2 code point. See <xreftarget="iana-settings" format="default"/>.</t>target='iana-settings'/>.</t> <t>As QUIC streams might arrive out of order, endpoints are advised not to wait for the peers' settings to arrive before responding to other streams. See <xreftarget="settings-initialization" format="default"/>.</t>target='settings-initialization'/>.</t> </section> <sectionanchor="http2-error-codes" numbered="true" toc="default">anchor='http2-error-codes'> <name>HTTP/2 Error Codes</name> <t>QUIC has the same concepts of "stream" and "connection" errors that HTTP/2 provides. However, the differences between HTTP/2 and HTTP/3 mean that error codes are not directly portable between versions.</t> <t>The HTTP/2 error codes defined in <xrefsection="7" sectionFormat="of" target="HTTP2" format="default"/>section='7' sectionFormat='of' target='RFC9113'/> logically map to the HTTP/3 error codes as follows:</t> <dl><dt> NO_ERROR (0x0): </dt><dt>NO_ERROR (0x00):</dt> <dd><t>H3_NO_ERROR<t><xref format='none' target='H3_NO_ERROR'>H3_NO_ERROR</xref><iref item='H3_NO_ERROR'/> in <xreftarget="http-error-codes" format="default"/>.</t>target='http-error-codes'/>.</t> </dd><dt> PROTOCOL_ERROR (0x1): </dt><dt>PROTOCOL_ERROR (0x01):</dt> <dd> <t>This is mapped toH3_GENERAL_PROTOCOL_ERROR<xref format='none' target='H3_GENERAL_PROTOCOL_ERROR'>H3_GENERAL_PROTOCOL_ERROR</xref><iref item='H3_GENERAL_PROTOCOL_ERROR'/> except in cases where more specific error codes have been defined. Such cases includeH3_FRAME_UNEXPECTED, H3_MESSAGE_ERROR,<xref format='none' target='H3_FRAME_UNEXPECTED'>H3_FRAME_UNEXPECTED</xref><iref item='H3_FRAME_UNEXPECTED'/>, <xref format='none' target='H3_MESSAGE_ERROR'>H3_MESSAGE_ERROR</xref><iref item='H3_MESSAGE_ERROR'/>, andH3_CLOSED_CRITICAL_STREAM<xref format='none' target='H3_CLOSED_CRITICAL_STREAM'>H3_CLOSED_CRITICAL_STREAM</xref><iref item='H3_CLOSED_CRITICAL_STREAM'/> defined in <xreftarget="http-error-codes" format="default"/>.</t>target='http-error-codes'/>.</t> </dd><dt> INTERNAL_ERROR (0x2): </dt><dt>INTERNAL_ERROR (0x02):</dt> <dd><t>H3_INTERNAL_ERROR<t><xref format='none' target='H3_INTERNAL_ERROR'>H3_INTERNAL_ERROR</xref><iref item='H3_INTERNAL_ERROR'/> in <xreftarget="http-error-codes" format="default"/>.</t>target='http-error-codes'/>.</t> </dd><dt> FLOW_CONTROL_ERROR (0x3): </dt><dt>FLOW_CONTROL_ERROR (0x03):</dt> <dd> <t>Not applicable, since QUIC handles flow control.</t> </dd><dt> SETTINGS_TIMEOUT (0x4): </dt><dt>SETTINGS_TIMEOUT (0x04):</dt> <dd> <t>Not applicable, since no acknowledgment ofSETTINGS<xref format='none' target='frame-settings'>SETTINGS</xref><iref item='SETTINGS'/> is defined.</t> </dd><dt> STREAM_CLOSED (0x5): </dt><dt>STREAM_CLOSED (0x05):</dt> <dd> <t>Not applicable, since QUIC handles stream management.</t> </dd><dt> FRAME_SIZE_ERROR (0x6): </dt><dt>FRAME_SIZE_ERROR (0x06):</dt> <dd><t>H3_FRAME_ERROR<t><xref format='none' target='H3_FRAME_ERROR'>H3_FRAME_ERROR</xref><iref item='H3_FRAME_ERROR'/> error code defined in <xreftarget="http-error-codes" format="default"/>.</t>target='http-error-codes'/>.</t> </dd><dt> REFUSED_STREAM (0x7): </dt><dt>REFUSED_STREAM (0x07):</dt> <dd><t>H3_REQUEST_REJECTED<t><xref format='none' target='H3_REQUEST_REJECTED'>H3_REQUEST_REJECTED</xref><iref item='H3_REQUEST_REJECTED'/> (in <xreftarget="http-error-codes" format="default"/>)target='http-error-codes'/>) is used to indicate that a request was not processed. Otherwise, not applicable because QUIC handles stream management.</t> </dd><dt> CANCEL (0x8): </dt><dt>CANCEL (0x08):</dt> <dd><t>H3_REQUEST_CANCELLED<t><xref format='none' target='H3_REQUEST_CANCELLED'>H3_REQUEST_CANCELLED</xref><iref item='H3_REQUEST_CANCELLED'/> in <xreftarget="http-error-codes" format="default"/>.</t>target='http-error-codes'/>.</t> </dd><dt> COMPRESSION_ERROR (0x9): </dt><dt>COMPRESSION_ERROR (0x09):</dt> <dd> <t>Multiple error codes are defined in <xreftarget="QPACK" format="default"/>.</t>target='RFC9204'/>.</t> </dd><dt> CONNECT_ERROR (0xa): </dt><dt>CONNECT_ERROR (0x0a):</dt> <dd><t>H3_CONNECT_ERROR<t><xref format='none' target='H3_CONNECT_ERROR'>H3_CONNECT_ERROR</xref><iref item='H3_CONNECT_ERROR'/> in <xreftarget="http-error-codes" format="default"/>.</t>target='http-error-codes'/>.</t> </dd><dt> ENHANCE_YOUR_CALM (0xb): </dt><dt>ENHANCE_YOUR_CALM (0x0b):</dt> <dd><t>H3_EXCESSIVE_LOAD<t><xref format='none' target='H3_EXCESSIVE_LOAD'>H3_EXCESSIVE_LOAD</xref><iref item='H3_EXCESSIVE_LOAD'/> in <xreftarget="http-error-codes" format="default"/>.</t>target='http-error-codes'/>.</t> </dd><dt> INADEQUATE_SECURITY (0xc): </dt><dt>INADEQUATE_SECURITY (0x0c):</dt> <dd> <t>Not applicable, since QUIC is assumed to provide sufficient security on all connections.</t> </dd><dt> HTTP_1_1_REQUIRED (0xd): </dt><dt>HTTP_1_1_REQUIRED (0x0d):</dt> <dd><t>H3_VERSION_FALLBACK<t><xref format='none' target='H3_VERSION_FALLBACK'>H3_VERSION_FALLBACK</xref><iref item='H3_VERSION_FALLBACK'/> in <xreftarget="http-error-codes" format="default"/>.</t>target='http-error-codes'/>.</t> </dd> </dl> <t>Error codes need to be defined for HTTP/2 and HTTP/3 separately. See <xreftarget="iana-error-codes" format="default"/>.</t>target='iana-error-codes'/>.</t> <sectionanchor="mapping-between-http2-and-http3-errors" numbered="true" toc="default">anchor='mapping-between-http2-and-http3-errors'> <name>MappingBetweenbetween HTTP/2 and HTTP/3 Errors</name> <t>An intermediary that converts between HTTP/2 and HTTP/3 may encounter error conditions from either upstream. It is useful to communicate the occurrence oferrorerrors to thedownstreamdownstream, but error codes largely reflect connection-local problems that generally do not make sense to propagate.</t> <t>An intermediary that encounters an error from an upstream origin can indicate this by sending an HTTP status code such as502,502 (Bad Gateway), which is suitable for a broad class of errors.</t> <t>There are some rare cases where it is beneficial to propagate the error by mapping it to the closest matching error type to the receiver. For example, an intermediary that receives an HTTP/2stream error<xref format='none' target='errors'>stream error</xref><iref item='stream error'/> of type REFUSED_STREAM from the origin has a clear signal that the request was not processed and that the request is safe to retry. Propagating this error condition to the client as an HTTP/3stream error<xref format='none' target='errors'>stream error</xref><iref item='stream error'/> of typeH3_REQUEST_REJECTED<xref format='none' target='H3_REQUEST_REJECTED'>H3_REQUEST_REJECTED</xref><iref item='H3_REQUEST_REJECTED'/> allows the client to take the action it deems most appropriate. In the reverse direction, the intermediary might deem it beneficial to pass on client request cancellations that are indicated by terminating a stream withH3_REQUEST_CANCELLED;<xref format='none' target='H3_REQUEST_CANCELLED'>H3_REQUEST_CANCELLED</xref><iref item='H3_REQUEST_CANCELLED'/>; see <xreftarget="request-cancellation" format="default"/>.</t>target='request-cancellation'/>.</t> <t>Conversion between errors is described in the logical mapping. The error codes are defined in non-overlapping spaces in order to protect against accidental conversion that could result in the use of inappropriate or unknown error codes for the target version. An intermediary is permitted to promotestream errors<xref format='none' target='errors'>stream errors</xref><iref item='stream error'/> toconnection errors<xref format='none' target='errors'>connection errors</xref><iref item='connection error'/> but they should be aware of the cost to the HTTP/3 connection for what might be a temporary or intermittent error.</t> </section> </section> </section> <sectionanchor="change-log" numbered="true" toc="default"> <name>Change Log</name> <ul empty="true" spacing="normal"> <li> <strong>RFC Editor's Note:</strong> Please remove this section prior to publication of a final version of this document.</li> </ul> <section anchor="since-draft-ietf-quic-http-32" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-32</name> <ul spacing="normal"> <li>Removed draft version guidance; added final version string</li> <li>Added H3_MESSAGE_ERROR for malformed messages</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-31" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-31</name> <t>Editorial changes only.</t> </section> <section anchor="since-draft-ietf-quic-http-30" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-30</name> <t>Editorial changes only.</t> </section> <section anchor="since-draft-ietf-quic-http-29" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-29</name> <ul spacing="normal"> <li>Require a connection error if a reserved frame type that corresponds to a frame in HTTP/2 is received (#3991, #3993)</li> <li>Require a connection error if a reserved setting that corresponds to a setting in HTTP/2 is received (#3954, #3955)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-28" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-28</name> <ul spacing="normal"> <li>CANCEL_PUSH is recommended even when the stream is reset (#3698, #3700)</li> <li>Use H3_ID_ERROR when GOAWAY contains a larger identifier (#3631, #3634)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-27" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-27</name> <ul spacing="normal"> <li>Updated text to refer to latest HTTP revisions</li> <li>Use the HTTP definition of authority for establishing and coalescing connections (#253, #2223, #3558)</li> <li>Define use of GOAWAY from both endpoints (#2632, #3129)</li> <li>Require either :authority or Host if the URI scheme has a mandatory authority component (#3408, #3475)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-26" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-26</name> <ul spacing="normal"> <li>No changes</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-25" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-25</name> <ul spacing="normal"> <li>Require QUICv1 for HTTP/3 (#3117, #3323)</li> <li>Remove DUPLICATE_PUSH and allow duplicate PUSH_PROMISE (#3275, #3309)</li> <li>Clarify the definition of "malformed" (#3352, #3345)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-24" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-24</name> <ul spacing="normal"> <li>Removed H3_EARLY_RESPONSE error code; H3_NO_ERROR is recommended instead (#3130,#3208)</li> <li>Unknown error codes are equivalent to H3_NO_ERROR (#3276,#3331)</li> <li>Some error codes are reserved for greasing (#3325,#3360)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-23" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-23</name> <ul spacing="normal"> <li>Removed <tt>quic</tt> Alt-Svc parameter (#3061,#3118)</li> <li>Clients need not persist unknown settings for use in 0-RTT (#3110,#3113)</li> <li>Clarify error cases around CANCEL_PUSH (#2819,#3083)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-22" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-22</name> <ul spacing="normal"> <li>Removed priority signaling (#2922,#2924)</li> <li> <t>Further changes to error codes (#2662,#2551): </t> <ul spacing="normal"> <li>Error codes renumbered</li> <li>HTTP_MALFORMED_FRAME replaced by HTTP_FRAME_ERROR, HTTP_ID_ERROR, and others</li> </ul> </li> <li>Clarify how unknown frame types interact with required frame sequence (#2867,#2858)</li> <li>Describe interactions with the transport in terms of defined interface terms (#2857,#2805)</li> <li>Require the use of the <tt>http-opportunistic</tt> resource (RFC 8164) when scheme is <tt>http</tt> (#2439,#2973)</li> <li>Settings identifiers cannot be duplicated (#2979)</li> <li> <t>Changes to SETTINGS frames in 0-RTT (#2972,#2790,#2945): </t> <ul spacing="normal"> <li>Servers must send all settings with non-default values in their SETTINGS frame, even when resuming</li> <li>If a client doesn't have settings associated with a 0-RTT ticket, it uses the defaults</li> <li>Servers can't accept early data if they cannot recover the settings the client will have remembered</li> </ul> </li> <li>Clarify that Upgrade and the 101 status code are prohibited (#2898,#2889)</li> <li>Clarify that frame types reserved for greasing can occur on any stream, but frame types reserved due to HTTP/2 correspondence are prohibited (#2997,#2692,#2693)</li> <li>Unknown error codes cannot be treated as errors (#2998,#2816)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-21" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-21</name> <t>No changes</t> </section> <section anchor="since-draft-ietf-quic-http-20" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-20</name> <ul spacing="normal"> <li>Prohibit closing the control stream (#2509, #2666)</li> <li>Change default priority to use an orphan node (#2502, #2690)</li> <li>Exclusive priorities are restored (#2754, #2781)</li> <li>Restrict use of frames when using CONNECT (#2229, #2702)</li> <li>Close and maybe reset streams if a connection error occurs for CONNECT (#2228, #2703)</li> <li>Encourage provision of sufficient unidirectional streams for QPACK (#2100, #2529, #2762)</li> <li>Allow extensions to use server-initiated bidirectional streams (#2711, #2773)</li> <li>Clarify use of maximum header list size setting (#2516, #2774)</li> <li> <t>Extensive changes to error codes and conditions of their sending </t> <ul spacing="normal"> <li>Require connection errors for more error conditions (#2511, #2510)</li> <li>Updated the error codes for illegal GOAWAY frames (#2714, #2707)</li> <li>Specified error code for HEADERS on control stream (#2708)</li> <li>Specified error code for servers receiving PUSH_PROMISE (#2709)</li> <li>Specified error code for receiving DATA before HEADERS (#2715)</li> <li>Describe malformed messages and their handling (#2410, #2764)</li> <li>Remove HTTP_PUSH_ALREADY_IN_CACHE error (#2812, #2813)</li> <li>Refactor Push ID related errors (#2818, #2820)</li> <li>Rationalize HTTP/3 stream creation errors (#2821, #2822)</li> </ul> </li> </ul> </section> <section anchor="since-draft-ietf-quic-http-19" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-19</name> <ul spacing="normal"> <li>SETTINGS_NUM_PLACEHOLDERS is 0x9 (#2443,#2530)</li> <li>Non-zero bits in the Empty field of the PRIORITY frame MAY be treated as an error (#2501)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-18" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-18</name> <ul spacing="normal"> <li>Resetting streams following a GOAWAY is recommended, but not required (#2256,#2457)</li> <li> <t>Use variable-length integers throughout (#2437,#2233,#2253,#2275) </t> <ul spacing="normal"> <li>Variable-length frame types, stream types, and settings identifiers</li> <li>Renumbered stream type assignments</li> <li>Modified associated reserved values</li> </ul> </li> <li>Frame layout switched from Length-Type-Value to Type-Length-Value (#2395,#2235)</li> <li>Specified error code for servers receiving DUPLICATE_PUSH (#2497)</li> <li>Use connection error for invalid PRIORITY (#2507, #2508)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-17" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-17</name> <ul spacing="normal"> <li>HTTP_REQUEST_REJECTED is used to indicate a request can be retried (#2106, #2325)</li> <li>Changed error code for GOAWAY on the wrong stream (#2231, #2343)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-16" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-16</name> <ul spacing="normal"> <li>Rename "HTTP/QUIC" to "HTTP/3" (#1973)</li> <li> <t>Changes to PRIORITY frame (#1865, #2075) </t> <ul spacing="normal"> <li>Permitted as first frame of request streams</li> <li>Remove exclusive reprioritization</li> <li>Changes to Prioritized Element Type bits</li> </ul> </li> <li>Define DUPLICATE_PUSH frame to refer to another PUSH_PROMISE (#2072)</li> <li>Set defaults for settings, allow request before receiving SETTINGS (#1809, #1846, #2038)</li> <li>Clarify message processing rules for streams that aren't closed (#1972, #2003)</li> <li>Removed reservation of error code 0 and moved HTTP_NO_ERROR to this value (#1922)</li> <li>Removed prohibition of zero-length DATA frames (#2098)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-15" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-15</name> <t>Substantial editorial reorganization; no technical changes.</t> </section> <section anchor="since-draft-ietf-quic-http-14" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-14</name> <ul spacing="normal"> <li>Recommend sensible values for QUIC transport parameters (#1720,#1806)</li> <li>Define error for missing SETTINGS frame (#1697,#1808)</li> <li>Setting values are variable-length integers (#1556,#1807) and do not have separate maximum values (#1820)</li> <li>Expanded discussion of connection closure (#1599,#1717,#1712)</li> <li>HTTP_VERSION_FALLBACK falls back to HTTP/1.1 (#1677,#1685)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-13" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-13</name> <ul spacing="normal"> <li>Reserved some frame types for grease (#1333, #1446)</li> <li>Unknown unidirectional stream types are tolerated, not errors; some reserved for grease (#1490, #1525)</li> <li>Require settings to be remembered for 0-RTT, prohibit reductions (#1541, #1641)</li> <li>Specify behavior for truncated requests (#1596, #1643)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-12" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-12</name> <ul spacing="normal"> <li>TLS SNI extension isn't mandatory if an alternative method is used (#1459, #1462, #1466)</li> <li>Removed flags from HTTP/3 frames (#1388, #1398)</li> <li>Reserved frame types and settings for use in preserving extensibility (#1333, #1446)</li> <li>Added general error code (#1391, #1397)</li> <li>Unidirectional streams carry a type byte and are extensible (#910,#1359)</li> <li>Priority mechanism now uses explicit placeholders to enable persistent structure in the tree (#441,#1421,#1422)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-11" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-11</name> <ul spacing="normal"> <li>Moved QPACK table updates and acknowledgments to dedicated streams (#1121, #1122, #1238)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-10" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-10</name> <ul spacing="normal"> <li>Settings need to be remembered when attempting and accepting 0-RTT (#1157, #1207)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-09" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-09</name> <ul spacing="normal"> <li>Selected QCRAM for header compression (#228, #1117)</li> <li>The server_name TLS extension is now mandatory (#296, #495)</li> <li>Specified handling of unsupported versions in Alt-Svc (#1093, #1097)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-08" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-08</name> <ul spacing="normal"> <li>Clarified connection coalescing rules (#940, #1024)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-07" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-07</name> <ul spacing="normal"> <li>Changes for integer encodings in QUIC (#595,#905)</li> <li>Use unidirectional streams as appropriate (#515, #240, #281, #886)</li> <li>Improvement to the description of GOAWAY (#604, #898)</li> <li>Improve description of server push usage (#947, #950, #957)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-06" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-06</name> <ul spacing="normal"> <li>Track changes in QUIC error code usage (#485)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-05" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-05</name> <ul spacing="normal"> <li>Made push ID sequential, add MAX_PUSH_ID, remove SETTINGS_ENABLE_PUSH (#709)</li> <li>Guidance about keep-alive and QUIC PINGs (#729)</li> <li>Expanded text on GOAWAY and cancellation (#757)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-04" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-04</name> <ul spacing="normal"> <li>Cite RFC 5234 (#404)</li> <li>Return to a single stream per request (#245,#557)</li> <li>Use separate frame typeanchor='acknowledgments' numbered='false'> <name>Acknowledgments</name> <t><contact fullname='Robbie Shade'/> andsettings registries from HTTP/2 (#81)</li> <li>SETTINGS_ENABLE_PUSH instead of SETTINGS_DISABLE_PUSH (#477)</li> <li>Restored GOAWAY (#696)</li> <li>Identify server push using Push ID rather than a stream ID (#702,#281)</li> <li>DATA frames cannot be empty (#700)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-03" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-03</name> <t>None.</t> </section> <section anchor="since-draft-ietf-quic-http-02" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-02</name> <ul spacing="normal"> <li>Track changes in transport draft</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-01" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-01</name> <ul spacing="normal"> <li> <t>SETTINGS changes (#181): </t> <ul spacing="normal"> <li>SETTINGS can be sent only once at<contact fullname='Mike Warres'/> were thestartauthors of draft-shade-quic-http2-mapping, aconnection; no changes thereafter</li> <li>SETTINGS_ACK removed</li> <li>Settings can only occur in the SETTINGS frame a single time</li> <li>Boolean format updated</li> </ul> </li> <li>Alt-Svc parameter changed from "v" to "quic"; format updated (#229)</li> <li>Closing the connection control stream or any message control stream is a fatal error (#176)</li> <li>HPACK Sequence counter can wrap (#173)</li> <li>0-RTT guidance added</li> <li>Guide to differences from HTTP/2 and porting HTTP/2 extensions added (#127,#242)</li> </ul> </section> <section anchor="since-draft-ietf-quic-http-00" numbered="true" toc="default"> <name>Since draft-ietf-quic-http-00</name> <ul spacing="normal"> <li>Changed "HTTP/2-over-QUIC" to "HTTP/QUIC" throughout (#11,#29)</li> <li>Changed from using HTTP/2 framing within Stream 3 to new framing format and two-stream-per-request model (#71,#72,#73)</li> <li>Adopted SETTINGS format from draft-bishop-httpbis-extended-settings-01</li> <li>Reworked SETTINGS_ACK to account for indeterminate inter-stream order (#75)</li> <li>Described CONNECT pseudo-method (#95)</li> <li>Updated ALPN token and Alt-Svc guidance (#13,#87)</li> <li>Application-layer-defined error codes (#19,#74)</li> </ul> </section> <section anchor="since-draft-shade-quic-http2-mapping-00" numbered="true" toc="default"> <name>Since draft-shade-quic-http2-mapping-00</name> <ul spacing="normal"> <li>Adopted as base for draft-ietf-quic-http</li> <li>Updated authors/editors list</li> </ul> </section> </section> <section numbered="false" anchor="acknowledgments" toc="default"> <name>Acknowledgments</name> <t>The original authorsprecursor of thisspecification were Robbie Shade and Mike Warres.</t>document.</t> <t>The IETF QUIC Working Group received an enormous amount of support from many people. Among others, the following people provided substantial contributions to this document:</t> <ulspacing="normal"> <li>Bence Beky</li> <li>Daanspacing='compact'> <li> <t><contact fullname="Bence Beky"/></t> </li> <li> <t><contact fullname="Daan DeMeyer</li> <li>Martin Duke</li> <li>Roy Fielding</li> <li>Alan Frindell</li> <li>Alessandro Ghedini</li> <li>Nick Harper</li> <li>Ryan Hamilton</li> <li>Christian Huitema</li> <li>Subodh Iyengar</li> <li>Robin Marx</li> <li>Patrick McManus</li> <li>Luca Niccolini</li>Meyer"/></t> </li> <li><t> <contact<t><contact fullname="Martin Duke"/></t> </li> <li> <t><contact fullname="Roy Fielding"/></t> </li> <li> <t><contact fullname="Alan Frindell"/></t> </li> <li> <t><contact fullname="Alessandro Ghedini"/></t> </li> <li> <t><contact fullname="Nick Harper"/></t> </li> <li> <t><contact fullname="Ryan Hamilton"/></t> </li> <li> <t><contact fullname="Christian Huitema"/></t> </li> <li> <t><contact fullname="Subodh Iyengar"/></t> </li> <li> <t><contact fullname="Robin Marx"/></t> </li> <li> <t><contact fullname="Patrick McManus"/></t> </li> <li> <t><contact fullname="Luca Niccolini"/></t> </li> <li> <t><contact asciiFullname="Kazuho Oku" fullname="奥一穂"/> </t>一穂"/></t> </li> <li> <t><contact fullname="Lucas Pardue"/></t> </li> <li> <t><contact fullname="Roberto Peon"/></t> </li> <li> <t><contact fullname="Julian Reschke"/></t> </li> <li> <t><contact fullname="Eric Rescorla"/></t> </li> <li> <t><contact fullname="Martin Seemann"/></t> </li> <li> <t><contact fullname="Ben Schwartz"/></t> </li> <li> <t><contact fullname="Ian Swett"/></t> </li> <li> <t><contact fullname="Willy Taureau"/></t> </li> <li> <t><contact fullname="Martin Thomson"/></t> </li> <li> <t><contact fullname="Dmitri Tikhonov"/></t> </li> <li> <t><contact fullname="Tatsuhiro Tsujikawa"/></t> </li><li>Lucas Pardue</li> <li>Roberto Peon</li> <li>Julian Reschke</li> <li>Eric Rescorla</li> <li>Martin Seemann</li> <li>Ben Schwartz</li> <li>Ian Swett</li> <li>Willy Taureau</li> <li>Martin Thomson</li> <li>Dmitri Tikhonov</li> <li>Tatsuhiro Tsujikawa</li></ul> <t>A portion ofMike's<contact fullname='Mike Bishop'/>'s contribution was supported by Microsoft during his employment there.</t> </section> </back><!-- ##markdown-source: H4sIAOrmGWAAA8S963bbWJIm+n8/BVq5ZqVUQzIt23kpe2pqlLKcqR7fRlJW dc2sWR6QhCS0SYANgJJZruxnmWc5T3bivmMDoOys6rNOre60TRIb+xI7rl9E TKfT0JXdqniW/bzbFE1XfOyyqyav2uuiyd41dVcv6lX2p6Jpy7rKnmSHP19d vfvmyVHI5/OmuIPH6N9hWS+qfA3DLJv8upuWRXc9/bdtuZjedt1m+uRpWOYd fPv40ePj6aPH8H9hAR/c1M3uWdZ2y1BummdZ12zb7vGjR7+Hr/OmyJ/xVDZ1 04X7uvlw09TbzbPsf/xyfhpC2+XV8n2+qisYd1e0YVM+y/4XzHeStfBAU1y3 8Lfdmv8C81vnm01Z3fzvEPJtd1s3z8I0ZPC/smqfZa9n2Y9le1tv6CNeyuvy Q+E/rZubZ9nJh3ydl/TvAv6yepat5/ST/1bcFf+2La7r7Wxe0PdNjftaLMuu bkKo6madd+Vd8SzAt7iG6dXFyZvLd28vrp7R7+UgDvA7eFH2y4t30x/ztlhm r7errtysio/wd1h1dlkstk0Rd+eAnh9sMX7YFk1ZtGV1XfNLsuy86oqmKrrp Czyq4Yl1OioeGz6g28WPT+VP2bh/nmXnu6K6yRv7nHfvn/MqH3xFW/gyb7vV zj5Ltmn0HXA4V7f1uq2r3jte501XVoMv6S2v67+Wq1U+/ho8gXcnp/+9t/H0 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