path: root/doc/rfc/rfc7464.txt

Internet Engineering Task Force (IETF)                       N. Williams
Request for Comments: 7464                                  Cryptonector
Category: Standards Track                                  February 2015
ISSN: 2070-1721


            JavaScript Object Notation (JSON) Text Sequences

Abstract

   This document describes the JavaScript Object Notation (JSON) text
   sequence format and associated media type "application/json-seq".  A
   JSON text sequence consists of any number of JSON texts, all encoded
   in UTF-8, each prefixed by an ASCII Record Separator (0x1E), and each
   ending with an ASCII Line Feed character (0x0A).

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc7464.

Copyright Notice

   Copyright (c) 2015 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.







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Table of Contents

   1. Introduction and Motivation .....................................2
      1.1. Conventions Used in This Document ..........................2
   2. JSON Text Sequence Format .......................................3
      2.1. JSON Text Sequence Parsing .................................3
      2.2. JSON Text Sequence Encoding ................................4
      2.3. Incomplete/Invalid JSON Texts Need Not Be Fatal ............4
      2.4. Top-Level Values: numbers, true, false, and null ...........5
   3. Security Considerations .........................................6
   4. IANA Considerations .............................................6
   5. Normative References ............................................7
   Acknowledgements ...................................................8
   Author's Address ...................................................8

1.  Introduction and Motivation

   The JavaScript Object Notation (JSON) [RFC7159] is a very handy
   serialization format.  However, when serializing a large sequence of
   values as an array, or a possibly indeterminate-length or never-
   ending sequence of values, JSON becomes difficult to work with.

   Consider a sequence of one million values, each possibly one kilobyte
   when encoded -- roughly one gigabyte.  It is often desirable to
   process such a dataset in an incremental manner without having to
   first read all of it before beginning to produce results.
   Traditionally, the way to do this with JSON is to use a "streaming"
   parser, but these are not widely available, widely used, or easy to
   use.

   This document describes the concept and format of "JSON text
   sequences", which are specifically not JSON texts themselves but are
   composed of (possible) JSON texts.  JSON text sequences can be parsed
   (and produced) incrementally without having to have a streaming
   parser (nor streaming encoder).

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].









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2.  JSON Text Sequence Format

   Two different sets of ABNF rules are provided for the definition of
   JSON text sequences: one for parsers and one for encoders.  Having
   two different sets of rules permits recovery by parsers from
   sequences where some of the elements are truncated for whatever
   reason.  The syntax for parsers is specified in terms of octet
   strings that are then interpreted as JSON texts, if possible.  The
   syntax for encoders, on the other hand, assumes that sequence
   elements are not truncated.

   JSON text sequences MUST use UTF-8 encoding; other encodings of JSON
   (i.e., UTF-16 and UTF-32) MUST NOT be used.

2.1.  JSON Text Sequence Parsing

   The ABNF [RFC5234] for the JSON text sequence parser is as given in
   Figure 1.

      input-JSON-sequence = *(1*RS possible-JSON)
      RS = %x1E; "record separator" (RS), see RFC 20
               ; Also known as: Unicode Character INFORMATION SEPARATOR
               ;                TWO (U+001E)
      possible-JSON = 1*(not-RS); attempt to parse as UTF-8-encoded
                                ; JSON text (see RFC 7159)
      not-RS = %x00-1d / %x1f-ff; any octets other than RS

                     Figure 1: JSON Text Sequence ABNF

   In prose: a series of octet strings, each containing any octet other
   than a record separator (RS) (0x1E) [RFC20].  All octet strings are
   preceded by an RS byte.  Each octet string in the sequence is to be
   parsed as a JSON text in the UTF-8 encoding [RFC3629].

   If parsing of such an octet string as a UTF-8-encoded JSON text
   fails, the parser SHOULD nonetheless continue parsing the remainder
   of the sequence.  The parser can report such failures to
   applications, which might then choose to terminate parsing of a
   sequence.  Multiple consecutive RS octets do not denote empty
   sequence elements between them and can be ignored.

   This document does not define a mechanism for reliably identifying
   text sequence by position (for example, when sending individual
   elements of an array as unique text sequences).  For applications
   where truncation is a possibility, this means that intended sequence
   elements can be truncated and can even be missing entirely;
   therefore, a reference to an nth element would be unreliable.




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   There is no end of sequence indicator.

2.2.  JSON Text Sequence Encoding

   The ABNF for the JSON text sequence encoder is given in Figure 2.

      JSON-sequence = *(RS JSON-text LF)
      RS = %x1E; see RFC 20
               ; Also known as: Unicode Character INFORMATION SEPARATOR
               ;                TWO (U+001E)
      LF = %x0A; "line feed" (LF), see RFC 20
      JSON-text = <given by RFC 7159, using UTF-8 encoding>

                     Figure 2: JSON Text Sequence ABNF

   In prose: any number of JSON texts, each encoded in UTF-8 [RFC3629],
   each preceded by one ASCII RS character, and each followed by a line
   feed (LF).  Since RS is an ASCII control character, it may only
   appear in JSON strings in escaped form (see [RFC7159]), and since RS
   may not appear in JSON texts in any other form, RS unambiguously
   delimits the start of any element in the sequence.  RS is sufficient
   to unambiguously delimit all top-level JSON value types other than
   numbers.  Following each JSON text in the sequence with an LF allows
   detection of truncated JSON texts consisting of a number at the top-
   level; see Section 2.4.

   JSON text sequence encoders are expected to ensure that the sequence
   elements are properly formed.  When the JSON text sequence encoder
   does the JSON text encoding, the sequence elements will naturally be
   properly formed.  When the JSON text sequence encoder accepts
   already-encoded JSON texts, the JSON text sequence encoder ought to
   parse them before adding them to a sequence.

   Note that on some systems it"s possible to input RS by typing
   "ctrl-^"; on some system or applications, the correct sequence may be
   "ctrl-v ctrl-^".  This is helpful when constructing a sequence
   manually with a text editor.

2.3.  Incomplete/Invalid JSON Texts Need Not Be Fatal

   Per Section 2.1, JSON text sequence parsers should not abort when an
   octet string contains a malformed JSON text.  Instead, the JSON text
   sequence parser should skip to the next RS.  Such a situation may
   arise in contexts where, for example, data that is appended to log
   files to log files is truncated by the filesystem (e.g., due to a
   crash or administrative process termination).





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   Incremental JSON text parsers may be used, though of course failure
   to parse a given text may result after first producing some
   incremental parse results.

   Sequence parsers should have an option to warn about truncated JSON
   texts.

2.4.  Top-Level Values: numbers, true, false, and null

   While objects, arrays, and strings are self-delimited in JSON texts,
   numbers and the values 'true', 'false', and 'null' are not.  Only
   whitespace can delimit the latter four kinds of values.

   JSON text sequences use 0x0A as a "canary" octet to detect
   truncation.

   Parsers MUST check that any JSON texts that are a top-level number,
   or that might be 'true', 'false', or 'null', include JSON whitespace
   (at least one byte matching the "ws" ABNF rule from [RFC7159]) after
   that value; otherwise, the JSON-text may have been truncated.  Note
   that the LF following each JSON text matches the "ws" ABNF rule.

   Parsers MUST drop JSON-text sequence elements consisting of non-self-
   delimited top-level values that may have been truncated (that are not
   delimited by whitespace).  Parsers can report such texts as warnings
   (including, optionally, the parsed text and/or the original octet
   string).

   For example, '<RS>123<RS>' might have been intended to carry the top-
   level number 1234, but it got truncated.  Similarly, '<RS>true<RS>'
   might have been intended to carry the invalid text 'trueish'.
   '<RS>truefalse<RS>' is not two top-level values, 'true', and 'false';
   it is simply not a valid JSON text.

   Implementations may produce a value when parsing '<RS>"foo"<RS>'
   because their JSON text parser might be able to consume bytes
   incrementally; since the JSON text in this case is a self-delimiting
   top-level value, the parser can produce the result without consuming
   an additional byte.  Such implementations ought to skip to the next
   RS byte, possibly reporting any intervening non-whitespace bytes.

   Detection of truncation of non-self-delimited sequence elements
   (numbers, true, false, and null) is only possible when the sequence
   encoder produces or receives complete JSON texts.  Implementations
   where the sequence encoder is not also in charge of encoding the
   individual JSON texts should ensure that those JSON texts are
   complete.




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3.  Security Considerations

   All the security considerations of JSON [RFC7159] apply.  This format
   provides no cryptographic integrity protection of any kind.

   As usual, parsers must operate on input that is assumed to be
   untrusted.  This means that parsers must fail gracefully in the face
   of malicious inputs.

   Note that incremental JSON text parsers can produce partial results
   and later indicate failure to parse the remainder of a text.  A
   sequence parser that uses an incremental JSON text parser might treat
   a sequence like '<RS>"foo"<LF>456<LF><RS>' as a sequence of one
   element ("foo"), while a sequence parser that uses a non-incremental
   JSON text parser might treat the same sequence as being empty.  This
   effect, and texts that fail to parse and are ignored, can be used to
   smuggle data past sequence parsers that don't warn about JSON text
   failures.

   Repeated parsing and re-encoding of a JSON text sequence can result
   in the addition (or stripping) of trailing LF bytes from (to)
   individual sequence element JSON texts.  This can break signature
   validation.  JSON has no canonical form for JSON texts, therefore
   neither does the JSON text sequence format.

4.  IANA Considerations

   The MIME media type for JSON text sequences is application/json-seq.

   Type name: application

   Subtype name: json-seq

   Required parameters: N/A

   Optional parameters: N/A

   Encoding considerations: binary

   Security considerations: See RFC 7464, Section 3.

   Interoperability considerations: Described herein.

   Published specification: RFC 7464.







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   Applications that use this media type:

      <https://stedolan.github.io/jq>
      <https://github.com/mapbox/cligj>
      <https://github.com/hildjj/json-text-sequence>

   Fragment identifier considerations: N/A

   Additional information:

   o  Deprecated alias names for this type: N/A

   o  Magic number(s): N/A

   o  File extension(s): N/A

   o  Macintosh file type code(s): N/A

   Person & email address to contact for further information:

      json@ietf.org

   Intended usage: COMMON

   Author: Nicolas Williams (nico@cryptonector.com)

   Change controller: IETF

5.  Normative References

   [RFC20]    Cerf, V., "ASCII format for network interchange", STD 80,
              RFC 20, October 1969,
              <http://www.rfc-editor.org/info/rfc20>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003,
              <http://www.rfc-editor.org/info/rfc3629>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.






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   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, March 2014,
              <http://www.rfc-editor.org/info/rfc7159>.

Acknowledgements

   Phillip Hallam-Baker proposed the use of JSON text sequences for
   logfiles and pointed out the need for resynchronization.  Stephen
   Dolan created <https://github.com/stedolan/jq>, which uses something
   like JSON text sequences (with LF as the separator between texts on
   output, and requiring only such whitespace as needed to disambiguate
   on input).  Carsten Bormann suggested the use of ASCII RS, and Joe
   Hildebrand suggested the use of LF in addition to RS for
   disambiguating top-level number values.  Paul Hoffman shepherded the
   document.  Many others contributed reviews and comments on the JSON
   Working Group mailing list.

Author's Address

   Nicolas Williams
   Cryptonector, LLC

   EMail: nico@cryptonector.com




























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