Internet Engineering Task Force (IETF) T. Hansen
Request for Comments: 6839 AT&T Laboratories
Updates: 3023 A. Melnikov
Category: Informational Isode Ltd
ISSN: 2070-1721 January 2013
Additional Media Type Structured Syntax Suffixes
Abstract
A content media type name sometimes includes partitioned meta-
information distinguished by a structured syntax to permit noting an
attribute of the media as a suffix to the name. This document
defines several structured syntax suffixes for use with media type
registrations. In particular, it defines and registers the "+json",
"+ber", "+der", "+fastinfoset", "+wbxml" and "+zip" structured syntax
suffixes, and provides a media type structured syntax suffix
registration form for the "+xml" structured syntax suffix.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6839.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. When to Use These Structured Syntax Suffixes . . . . . . . . . 3
3. Initial Structured Syntax Suffix Definitions . . . . . . . . . 3
3.1. The +json Structured Syntax Suffix . . . . . . . . . . . . 3
3.2. The +ber Structured Syntax Suffix . . . . . . . . . . . . 5
3.3. The +der Structured Syntax Suffix . . . . . . . . . . . . 6
3.4. The +fastinfoset Structured Syntax Suffix . . . . . . . . 8
3.5. The +wbxml Structured Syntax Suffix . . . . . . . . . . . 9
3.6. The +zip Structured Syntax Suffix . . . . . . . . . . . . 10
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
4.1. The +xml Structured Syntax Suffix . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 13
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. Normative References . . . . . . . . . . . . . . . . . . . 13
6.2. Informative References . . . . . . . . . . . . . . . . . . 14
1. Introduction
[RFC3023] created the +xml suffix convention that can be used when
defining names for media types whose representation uses XML
underneath. That is, they could have been successfully parsed as if
the media type had been application/xml in addition to their being
parsed as their media type that is using the +xml suffix. [RFC6838]
defines the media type "Structured Syntax Suffix Registry" to be used
for such structured syntax suffixes.
A variety of structured syntax suffixes have already been used in
some media type registrations, in particular "+json", "+der",
"+fastinfoset", and "+wbxml". This document defines and registers
these structured syntax suffixes in the Structured Syntax Suffix
Registry, along with "+ber" and "+zip". In addition, this document
updates [RFC3023] to formally register the "+xml" structured syntax
suffix according to the procedure defined in [RFC6838].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. When to Use These Structured Syntax Suffixes
Each of the structured syntax suffixes defined in this document is
appropriate for use when the media type identifies the semantics of
the protocol payload. That is, knowing the semantics of the specific
media type provides for more specific processing of the content than
that afforded by generic processing of the underlying representation.
At the same time, using the suffix allows receivers of the media
types to do generic processing of the underlying representation in
cases where
they do not need to perform special handling of the particular
semantics of the exact media type, and
there is no special knowledge needed by such a generic processor
in order to parse that underlying representation other than what
would be needed to parse any example of that underlying
representation.
3. Initial Structured Syntax Suffix Definitions
3.1. The +json Structured Syntax Suffix
[RFC4627] defines the "application/json" media type. The suffix
"+json" MAY be used with any media type whose representation follows
that established for "application/json". The media type structured
syntax suffix registration form follows. See [RFC6838] for
definitions of each of the registration form headings.
Name: JavaScript Object Notation (JSON)
+suffix: +json
References: [RFC4627]
Encoding considerations: Per [RFC4627], JSON is allowed to be
represented using UTF-8, UTF-16, or UTF-32. When
JSON is written in UTF-8, JSON is 8bit compatible
([RFC2045]). When JSON is written in UTF-16 or
UTF-32, JSON is binary ([RFC2045]).
Fragment identifier considerations:
The syntax and semantics of fragment
identifiers specified for +json SHOULD be as
specified for "application/json". (At
publication of this document, there is no
fragment identification syntax defined for
"application/json".)
The syntax and semantics for fragment
identifiers for a specific "xxx/yyy+json"
SHOULD be processed as follows:
For cases defined in +json, where the
fragment identifier resolves per the +json
rules, then process as specified in +json.
For cases defined in +json, where the
fragment identifier does not resolve per
the +json rules, then process as specified
in "xxx/yyy+json".
For cases not defined in +json, then
process as specified in "xxx/yyy+json".
Interoperability considerations: n/a
Security considerations: See [RFC4627]
Contact: Apps Area Working Group (apps-discuss@ietf.org)
Author/Change controller: The Apps Area Working Group. IESG has
change control over this registration.
3.2. The +ber Structured Syntax Suffix
The ITU defined the Basic Encoding Rules (BER) media transfer syntax in
[ITU.X690.2008]. The suffix "+ber" MAY be used with any media type
whose representation follows the BER media transfer syntax. (The Expert
Reviewer for media type structured syntax suffix registrations ought
to be aware of the relationship between BER and DER to aid in
selecting the proper suffix.) The media type structured syntax
suffix registration form for +ber follows:
Name: Basic Encoding Rules (BER) media transfer syntax
+suffix: +ber
References: [ITU.X690.2008]
Encoding considerations: BER is a binary encoding.
Fragment identifier considerations:
At publication of this document, there is no
fragment identification syntax defined for
+ber.
The syntax and semantics for fragment
identifiers for a specific "xxx/yyy+ber"
SHOULD be processed as follows:
For cases defined in +ber, where the
fragment identifier resolves per the +ber
rules, then process as specified in +ber.
For cases defined in +ber, where the
fragment identifier does not resolve per
the +ber rules, then process as specified
in "xxx/yyy+ber".
For cases not defined in +ber, then process
as specified in "xxx/yyy+ber".
Interoperability considerations: n/a
Security considerations: Each individual media type registered with
a +ber suffix can have additional security
considerations.
BER has a type-length-value structure, and it is
easy to construct malicious content with invalid
length fields that can cause buffer overrun
conditions.
BER allows for arbitrary levels of nesting, which
may make it possible to construct malicious
content that will cause a stack overflow.
Interpreters of the BER structures should be
aware of these issues and should take appropriate
measures to guard against buffer overflows and
stack overruns in particular and malicious
content in general.
Contact: Apps Area Working Group (apps-discuss@ietf.org)
Author/Change controller: The Apps Area Working Group. IESG has
change control over this registration.
3.3. The +der Structured Syntax Suffix
The ITU defined the Distinguished Encoding Rules (DER) media transfer
syntax in [ITU.X690.2008]. The suffix "+der" MAY be used with any
media type whose representation follows the DER media transfer syntax.
(The Expert Reviewer for media type structured syntax suffix
registrations ought to be aware of the relationship between BER and
DER to aid in selecting the proper suffix.) The media type
structured syntax suffix registration form for +der follows:
Name: Distinguished Encoding Rules (DER) media transfer
syntax
+suffix: +der
References: [ITU.X690.2008]
Encoding considerations: DER is a binary encoding.
Fragment identifier considerations:
At publication of this document, there is no
fragment identification syntax defined for
+der.
The syntax and semantics for fragment
identifiers for a specific "xxx/yyy+der"
SHOULD be processed as follows:
For cases defined in +der, where the
fragment identifier resolves per the +der
rules, then process as specified in +der.
For cases defined in +der, where the
fragment identifier does not resolve per
the +der rules, then process as specified
in "xxx/yyy+der".
For cases not defined in +der, then process
as specified in "xxx/yyy+der".
Interoperability considerations: n/a
Security considerations: Each individual media type registered with
a +der suffix can have additional security
considerations.
DER has a type-length-value structure, and it is
easy to construct malicious content with invalid
length fields that can cause buffer overrun
conditions.
DER allows for arbitrary levels of nesting, which
may make it possible to construct malicious
content that will cause a stack overflow.
Interpreters of the DER structures should be
aware of these issues and should take appropriate
measures to guard against buffer overflows and
stack overruns in particular and malicious
content in general.
Contact: Apps Area Working Group (apps-discuss@ietf.org)
Author/Change controller: The Apps Area Working Group. IESG has
change control over this registration.
3.4. The +fastinfoset Structured Syntax Suffix
The ITU defined the Fast Infoset document format as a binary
representation of the XML Information Set in [ITU.X891.2005]. These
documents further define the "application/fastinfoset" media type.
The suffix "+fastinfoset" MAY be used with any media type whose
representation follows that established for "application/
fastinfoset". The media type structured syntax suffix registration
form follows:
Name: Fast Infoset document format
+suffix: +fastinfoset
References: [ITU.X891.2005]
Encoding considerations: Fast Infoset is a binary encoding. The
binary, quoted-printable, and base64 content-
transfer-encodings are suitable for use with Fast
Infoset.
Fragment identifier considerations:
The syntax and semantics of fragment
identifiers specified for +fastinfoset SHOULD
be as specified for "application/fastinfoset".
(At publication of this document, there is no
fragment identification syntax defined for
"application/fastinfoset".)
The syntax and semantics for fragment
identifiers for a specific "xxx/
yyy+fastinfoset" SHOULD be processed as
follows:
For cases defined in +fastinfoset, where
the fragment identifier resolves per the
+fastinfoset rules, then process as
specified in +fastinfoset.
For cases defined in +fastinfoset, where
the fragment identifier does not resolve
per the +fastinfoset rules, then process as
specified in "xxx/yyy+fastinfoset".
For cases not defined in +fastinfoset, then
process as specified in "xxx/
yyy+fastinfoset".
Interoperability considerations: n/a
Security considerations: There are no security considerations
inherent in Fast Infoset. Each individual media
type registered with a +fastinfoset suffix can
have additional security considerations.
Contact: Apps Area Working Group (apps-discuss@ietf.org)
Author/Change controller: The Apps Area Working Group. IESG has
change control over this registration.
3.5. The +wbxml Structured Syntax Suffix
The Wireless Application Protocol (WAP) Forum has defined the WAP
Binary XML (WBXML) document format as a binary representation of XML
in [WBXML]. This document further defines the "application/
vnd.wap.wbxml" media type. The suffix "+wbxml" MAY be used with any
media type whose representation follows that established for
"application/vnd.wap.wbxml". The media type structured syntax suffix
registration form follows:
Name: WAP Binary XML (WBXML) document format
+suffix: +wbxml
References: [WBXML]
Encoding considerations: WBXML is a binary encoding.
Fragment identifier considerations:
The syntax and semantics of fragment
identifiers specified for +wbxml SHOULD be as
specified for "application/vnd.wap.wbxml".
(At publication of this document, there is no
fragment identification syntax defined for
"application/vnd.wap.wbxml".)
The syntax and semantics for fragment
identifiers for a specific "xxx/yyy+wbxml"
SHOULD be processed as follows:
For cases defined in +wbxml, where the
fragment identifier resolves per the +wbxml
rules, then process as specified in +wbxml.
For cases defined in +wbxml, where the
fragment identifier does not resolve per
the +wbxml rules, then process as specified
in "xxx/yyy+wbxml".
For cases not defined in +wbxml, then
process as specified in "xxx/yyy+wbxml".
Interoperability considerations: n/a
Security considerations: There are no security considerations
inherent in WBXML. Each individual media type
registered with a +wbxml suffix can have
additional security considerations.
Contact: Apps Area Working Group (apps-discuss@ietf.org)
Author/Change controller: The Apps Area Working Group. IESG has
change control over this registration.
3.6. The +zip Structured Syntax Suffix
The ZIP format is a public domain, cross-platform, interoperable file
storage and transfer format, originally defined by PKWARE, Inc.; it
supports compression and encryption and is used as the underlying
representation by a variety of file formats. The media type
"application/zip" has been registered for such files. The suffix
"+zip" MAY be used with any media type whose representation follows
that established for "application/zip". The media type structured
syntax suffix registration form follows:
Name: ZIP file storage and transfer format
+suffix: +zip
References: [ZIP]
Encoding considerations: ZIP is a binary encoding.
Fragment identifier considerations:
The syntax and semantics of fragment
identifiers specified for +zip SHOULD be as
specified for "application/zip". (At
publication of this document, there is no
fragment identification syntax defined for
"application/zip".)
The syntax and semantics for fragment
identifiers for a specific "xxx/yyy+zip"
SHOULD be processed as follows:
For cases defined in +zip, where the
fragment identifier resolves per the +zip
rules, then process as specified in +zip.
For cases defined in +zip, where the
fragment identifier does not resolve per
the +zip rules, then process as specified
in "xxx/yyy+zip".
For cases not defined in +zip, then process
as specified in "xxx/yyy+zip".
Interoperability considerations: n/a
Security considerations: ZIP files support two forms of encryption:
Strong Encryption and AES 128-bit, 192-bit, and
256-bit encryption; see the specification for
further details. Each individual media type
registered with a +zip suffix can have additional
security considerations.
Contact: Apps Area Working Group (apps-discuss@ietf.org)
Author/Change controller: The Apps Area Working Group. IESG has
change control over this registration.
4. IANA Considerations
See the media type structured syntax suffix registration forms in
Sections 3.1 - 3.6.
4.1. The +xml Structured Syntax Suffix
The following structured syntax suffix registration for "+xml" shall
be used to reflect the information found in [RFC3023], with the
addition of fragment identifier considerations. (Note that [RFC3023]
is in the process of being updated by [XML-MEDIATYPES].)
Name: Extensible Markup Language (XML)
+suffix: +xml
References: [RFC3023]
Encoding considerations: Per [RFC3023], XML is allowed to be
represented using both 7-bit and 8-bit encodings.
When XML is written in UTF-8, XML is 8bit
compatible ([RFC2045]). When XML is written in
UTF-16 or UTF-32, XML is binary ([RFC2045]).
Fragment identifier considerations:
The syntax and semantics of fragment
identifiers specified for +xml SHOULD be as
specified for "application/xml". (At
publication of this document, the fragment
identification syntax considerations for
"application/xml" are defined in [RFC3023],
Sections 5 and 7.)
The syntax and semantics for fragment
identifiers for a specific "xxx/yyy+xml"
SHOULD be processed as follows:
For cases defined in +xml, where the
fragment identifier resolves per the +xml
rules, then process as specified in +xml.
For cases defined in +xml, where the
fragment identifier does not resolve per
the +xml rules, then process as specified
in "xxx/yyy+xml".
For cases not defined in +xml, then process
as specified in "xxx/yyy+xml".
Interoperability considerations: See [RFC3023].
Security considerations: See [RFC3023]
Contact: Apps Area Working Group (apps-discuss@ietf.org)
Author/Change controller: The Apps Area Working Group. IESG has
change control over this registration.
5. Security Considerations
See the Security Considerations sections found in the media type
structured syntax suffix registration forms from Sections 3 and 4.
When updating a +<suffix> registration, care should be taken to
review all previously-registered xxx/yyy+<suffix> media types as to
whether they might be affected by the updated +<suffix> registration.
Because the generic fragment identifier processing rules take
precedence over media-type-specific rules, introducing new or
changing existing definitions may break the existing registrations of
specific media types, as well as particular implementations of
applications that process affected media types. Such changes can
introduce interoperability and security issues.
When updating the fragment identifier processing rules for a specific
xxx/yyy+<suffix> media type, care should be taken to review the
generic fragment identifier processing rules for the +<suffix>
registration and not introduce any conflicts. Because the generic
fragment identifier processing rules take precedence over media-type-
specific rules, such conflicting processing requirements should be
ignored by an implementation, but such conflicts can introduce
interoperability and security issues.
Note that [FRAGID-BP] provides additional advice to designers of
fragment identifier rules for media type suffixes and specific media
types.
6. References
6.1. Normative References
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
[ITU.X690.2008]
International Telecommunications Union, "Recommendation
ITU-T X.690 | ISO/IEC 8825-1 (2008), ASN.1 encoding rules:
Specification of basic encoding Rules (BER), Canonical
encoding rules (CER) and Distinguished encoding rules
(DER)", ITU-T Recommendation X.690, November 2008.
[ITU.X891.2005]
International Telecommunications Union, "Recommendation
ITU-T X.891 | ISO/IEC 24824-1 (2007), Generic applications
of ASN.1: Fast infoset", ITU-T Recommendation X.891,
May 2005.
[WBXML] Open Mobile Alliance, "Binary XML Content Format
Specification", OMA Wireless Access Protocol WAP-192-
WBXML-20010725-a, July 2001.
[ZIP] PKWARE, Inc., "APPNOTE.TXT - .ZIP File Format
Specification", PKWARE .ZIP File Format Specification -
Version 6.3.2, September 2007.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
6.2. Informative References
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, January 2013.
[FRAGID-BP]
Tennison, J., "Best Practices for Fragment Identifiers and
Media Type Definitions", July 2012,
<http://www.w3.org/TR/fragid-best-practices/>.
[XML-MEDIATYPES]
Lilley, C., Makoto, M., Melnikov, A., and H. Thompson,
"XML Media Types", Work in Progress, November 2012.
Authors' Addresses
Tony Hansen
AT&T Laboratories
200 Laurel Ave. South
Middletown, NJ 07748
USA
EMail: tony+sss@maillennium.att.com
Alexey Melnikov
Isode Ltd
5 Castle Business Village
36 Station Road
Hampton, Middlesex TW12 2BX
UK
EMail: Alexey.Melnikov@isode.com