Operations Area Working Group D. Crockford Internet-Draft JSON.org Intended status: Standards Track June 06, 2013 Expires: December 08, 2013 The JSON Data Interchange Format draft-ietf-json-rfc4627bis-01 Abstract JSON is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on December 08, 2013. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Crockford Expires December 08, 2013 [Page 1] Internet-Draft JSON bis June 2013 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Conventions Used in This Document . . . . . . . . . . . . 2 1.2. Changes from RFC 4627 . . . . . . . . . . . . . . . . . . 3 2. JSON Grammar . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Values . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Objects . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.3. Arrays . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.4. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.5. Strings . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Parsers . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Generators . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7. Normative References . . . . . . . . . . . . . . . . . . . . 9 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction JSON is a text format for the serialization of structured data. It was inspired by the object literals of JavaScript, as defined in the ECMAScript Programming Language Standard, Fifth Edition[ECMA]. JSON can represent four primitive types (strings, numbers, booleans, and null) and two structured types (objects and arrays). A string is a sequence of zero or more characters. An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array. An array is an ordered sequence of zero or more values. The terms "object" and "array" come from the conventions of JavaScript. JSON's design goals were for it to be minimal, portable, textual, and a subset of JavaScript. JSON stands for JavaScript Object Notation. 1.1. Conventions Used in This Document 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]. Crockford Expires December 08, 2013 [Page 2] Internet-Draft JSON bis June 2013 The grammatical rules in this document are to be interpreted as described in [RFC5234]. 1.2. Changes from RFC 4627 This section lists all changes between this document and the text in RFC 4627. o Applied errata #607 from RFC 4627 to correctly align the artwork for the definition of "object". 2. JSON Grammar A JSON text is a sequence of tokens. The set of tokens includes six structural characters, strings, numbers, and three literal names. A JSON text is a serialized object or array. JSON-text = object / array These are the six structural characters: begin-array = ws %x5B ws ; [ left square bracket begin-object = ws %x7B ws ; { left curly bracket end-array = ws %x5D ws ; ] right square bracket end-object = ws %x7D ws ; } right curly bracket name-separator = ws %x3A ws ; : colon value-separator = ws %x2C ws ; , comma Insignificant whitespace is allowed before or after any of the six structural characters. ws = *( %x20 / ; Space %x09 / ; Horizontal tab %x0A / ; Line feed or New line %x0D ; Carriage return ) Crockford Expires December 08, 2013 [Page 3] Internet-Draft JSON bis June 2013 2.1. Values A JSON value MUST be an object, array, number, or string, or one of the following three literal names: false null true The literal names MUST be lowercase. No other literal names are allowed. value = false / null / true / object / array / number / string false = %x66.61.6c.73.65 ; false null = %x6e.75.6c.6c ; null true = %x74.72.75.65 ; true 2.2. Objects An object structure is represented as a pair of curly brackets surrounding zero or more name/value pairs (or members). A name is a string. A single colon comes after each name, separating the name from the value. A single comma separates a value from a following name. The names within an object SHOULD be unique. If a key is duplicated, a parser MAY reject. If it does not reject, then it MUST take only the last of the duplicated key pairs. object = begin-object [ member *( value-separator member ) ] end-object member = string name-separator value 2.3. Arrays An array structure is represented as square brackets surrounding zero or more values (or elements). Elements are separated by commas. array = begin-array [ value *( value-separator value ) ] end-array 2.4. Numbers A number is represented in base 10 with no superfluous leading zeroes or punctuation such as commas or spaces. It may have a preceding Crockford Expires December 08, 2013 [Page 4] Internet-Draft JSON bis June 2013 minus sign. It may have a "."-prefixed fractional part. It may have an exponent, prefixed by "e" or "E" and optionally "+" or "-". Numeric values that cannot be represented as sequences of digits (such as Infinity and NaN) are not permitted. number = [ minus ] int [ frac ] [ exp ] decimal-point = %x2E ; . digit1-9 = %x31-39 ; 1-9 e = %x65 / %x45 ; e E exp = e [ minus / plus ] 1*DIGIT frac = decimal-point 1*DIGIT int = zero / ( digit1-9 *DIGIT ) minus = %x2D ; - plus = %x2B ; + zero = %x30 ; 0 2.5. Strings The representation of strings is similar to conventions used in the C family of programming languages. A string is a sequence of code units wrapped with quotation marks. All characters may be placed within the quotation marks except for the characters that must be escaped: quotation mark, reverse solidus, and the control characters (U+0000 through U+001F). Any character may be escaped. If the character is in the Basic Multilingual Plane (U+0000 through U+FFFF), then it may be represented as a six-character sequence: a reverse solidus, followed by the lowercase letter u, followed by four hexadecimal digits that encode the character's Unicode code point. The hexadecimal letters A though F can be upper or lowercase. So, for example, a string containing only a single reverse solidus character may be represented as "\u005C". Crockford Expires December 08, 2013 [Page 5] Internet-Draft JSON bis June 2013 Alternatively, there are two-character sequence escape representations of some popular characters. So, for example, a string containing only a single reverse solidus character may be represented more compactly as "\\". string = quotation-mark *char quotation-mark char = unescaped / escape ( %x22 / ; " quotation mark U+0022 %x5C / ; \ reverse solidus U+005C %x2F / ; / solidus U+002F %x62 / ; b backspace U+0008 %x66 / ; f form feed U+000C %x6E / ; n line feed U+000A %x72 / ; r carriage return U+000D %x74 / ; t tab U+0009 %x75 4HEXDIG ) ; uXXXX U+XXXX escape = %x5C ; \ quotation-mark = %x22 ; " unescaped = %x20-21 / %x23-5B / %x5D-10FFFF The following four cases MUST all produce the same result: "\u002F" "\u002F" "\/" "/" To escape an extended character that is not in the Basic Multilingual Plane, the character is represented as a twelve-character sequence, encoding the UTF-16 surrogate pair. So for example, a string containing only the G clef character (U+1D11E) may be represented as "\uD834\uDD1E". A generator SHOULD NOT emit unpaired surrogates. A parser MAY reject JSON text containing unpaired surrogates. 3. Parsers A JSON parser transforms a JSON text into another representation. A JSON parser MUST accept all texts that conform to the JSON grammar. A JSON parser MAY accept non-JSON forms or extensions. Crockford Expires December 08, 2013 [Page 6] Internet-Draft JSON bis June 2013 An implementation may set limits on the size of texts that it accepts. An implementation may set limits on the maximum depth of nesting. An implementation may set limits on the range of numbers. An implementation may set limits on the length and character contents of strings. 4. Generators A JSON generator produces JSON text. The resulting text MUST strictly conform to the JSON grammar. 5. Security Considerations With any data format, it is important to encode correctly. Care must be taken when constructing JSON texts by concatenation. For example: account = 4627; comment = "\",\"account\":262"; // provided by attacker json_text = "(\"account\":" + account + ",\"comment\":\"" + comment + "\"}"; The result will be {"account":4627,"comment":"","account":262} which some parsers MAY see as being the same as {"comment":"","account":262} This confusion allows an attacker to modify the account property or any other property. It is much wiser to use JSON generators, which are available in many forms for most programming languages, to do the encoding, avoiding the confusion hazard. JSON is so similar to some programming languages that the native parsing ability of the language processors can be used to parse JSON texts. This should be avoided because the native parser will accept code which is not JSON. For example, JavaScript's eval() function is able parse JSON text, but is can also parse programs. If an attacker can inject code into the JSON text (as we saw above), then it can compromise the system. JSON parsers should always be used instead. Crockford Expires December 08, 2013 [Page 7] Internet-Draft JSON bis June 2013 The web browser's script tag is an alias for the eval() function. It should not be used to deliver JSON text to web browsers. 6. Examples This is a JSON object: { "Image": { "Width": 800, "Height": 600, "Title": "View from 15th Floor", "Thumbnail": { "Url": "http://www.example.com/image/481989943", "Height": 125, "Width": "100" }, "IDs": [116, 943, 234, 38793] } } Its Image member is an object whose Thumbnail member is an object and whose IDs member is an array of numbers. This is a JSON array containing two objects: [ { "precision": "zip", "Latitude": 37.7668, "Longitude": -122.3959, "Address": "", "City": "SAN FRANCISCO", "State": "CA", "Zip": "94107", "Country": "US" }, { "precision": "zip", "Latitude": 37.371991, "Longitude": -122.026020, "Address": "", "City": "SUNNYVALE", "State": "CA", "Zip": "94085", "Country": "US" } Crockford Expires December 08, 2013 [Page 8] Internet-Draft JSON bis June 2013 ] 7. Normative References [ECMA] European Computer Manufacturers Association, "ECMAScript Language Specification Fifth Edition ", December 2009, . [RFC0020] Cerf, V., "ASCII format for network interchange", RFC 20, October 1969. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. [UNICODE] The Unicode Consortium, "The Unicode Standard, Version 6.2 ", 2012, . Author's Address Douglas Crockford JSON.org Email: douglas@crockford.com Crockford Expires December 08, 2013 [Page 9]