Internet Engineering Task Force (IETF)                      T. Bray, Ed.
Request for Comments: 7493                           Textuality Services
Category: Standards Track                                     March 2015
ISSN: 2070-1721


                      The I-JSON Message Format

Abstract

  I-JSON (short for "Internet JSON") is a restricted profile of JSON
  designed to maximize interoperability and increase confidence that
  software can process it successfully with predictable results.

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/rfc7493.

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  . . . . . . . . . . . . . . . . . . . . . . . .   2
    1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
    1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   2
  2.  I-JSON Messages . . . . . . . . . . . . . . . . . . . . . . .   3
    2.1.  Encoding and Characters . . . . . . . . . . . . . . . . .   3
    2.2.  Numbers . . . . . . . . . . . . . . . . . . . . . . . . .   3
    2.3.  Object Constraints  . . . . . . . . . . . . . . . . . . .   3
  3.  Software Behavior . . . . . . . . . . . . . . . . . . . . . .   4
  4.  Recommendations for Protocol Design . . . . . . . . . . . . .   4
    4.1.  Top-Level Constructs  . . . . . . . . . . . . . . . . . .   4
    4.2.  Must-Ignore Policy  . . . . . . . . . . . . . . . . . . .   4
    4.3.  Time and Date Handling  . . . . . . . . . . . . . . . . .   5
    4.4.  Binary Data . . . . . . . . . . . . . . . . . . . . . . .   5
  5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
  6.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
  Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

  RFC 7159 describes the JSON data interchange format, which is widely
  used in Internet protocols.  For historical reasons, that
  specification allows the use of language idioms and text encoding
  patterns that are likely to lead to interoperability problems and
  software breakage, particularly when a program receiving JSON data
  uses automated software to map it into native programming-language
  structures or database records.  RFC 7159 describes practices that
  may be used to avoid these interoperability problems.

  This document specifies I-JSON, short for "Internet JSON".  The unit
  of definition is the "I-JSON message".  I-JSON messages are also
  "JSON texts" as defined in RFC 7159 but with certain extra
  constraints that enforce the good interoperability practices
  described in that specification.

1.1.  Terminology

  The terms "object", "member", "array", "number", "name", and "string"
  in this document are to be interpreted as described in RFC 7159
  [RFC7159].

1.2.  Requirements Language

  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 RFC 2119 [RFC2119].



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2.  I-JSON Messages

  An I-JSON message is a JSON text, as defined by RFC 7159.

2.1.  Encoding and Characters

  I-JSON messages MUST be encoded using UTF-8 [RFC3629].

  Object member names, and string values in arrays and object members,
  MUST NOT include code points that identify Surrogates or
  Noncharacters as defined by [UNICODE].

  This applies both to characters encoded directly in UTF-8 and to
  those which are escaped; thus, "\uDEAD" is invalid because it is an
  unpaired surrogate, while "\uD800\uDEAD" would be legal.

2.2.  Numbers

  Software that implements IEEE 754-2008 binary64 (double precision)
  numbers [IEEE754] is generally available and widely used.
  Implementations that generate I-JSON messages cannot assume that
  receiving implementations can process numeric values with greater
  magnitude or precision than provided by those numbers.  I-JSON
  messages SHOULD NOT include numbers that express greater magnitude or
  precision than an IEEE 754 double precision number provides, for
  example, 1E400 or 3.141592653589793238462643383279.

  An I-JSON sender cannot expect a receiver to treat an integer whose
  absolute value is greater than 9007199254740991 (i.e., that is
  outside the range [-(2**53)+1, (2**53)-1]) as an exact value.

  For applications that require the exact interchange of numbers with
  greater magnitude or precision, it is RECOMMENDED to encode them in
  JSON string values.  This requires that the receiving program
  understand the intended semantic of the value.  An example would be
  64-bit integers, even though modern hardware can deal with them,
  because of the limited scope of JavaScript numbers.

2.3.  Object Constraints

  Objects in I-JSON messages MUST NOT have members with duplicate
  names.  In this context, "duplicate" means that the names, after
  processing any escaped characters, are identical sequences of Unicode
  characters.







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  The order of object members in an I-JSON message does not change the
  meaning of an I-JSON message.  A receiving implementation MAY treat
  two I-JSON messages as equivalent if they differ only in the order of
  the object members.

3.  Software Behavior

  A major advantage of using I-JSON is that receivers can avoid
  ambiguous semantics in the JSON messages they receive.  This allows
  receivers to reject or otherwise disregard messages that do not
  conform to the requirements in this document for I-JSON messages.
  Protocols that use I-JSON messages can be written so that receiving
  implementations are required to reject (or, as in the case of
  security protocols, not trust) messages that do not satisfy the
  constraints of I-JSON.

  Designers of protocols that use I-JSON messages SHOULD provide a way,
  in this case, for the receiver of the erroneous data to signal the
  problem to the sender.

4.  Recommendations for Protocol Design

  I-JSON is designed for use in Internet protocols.  The following
  recommendations apply to the use of I-JSON in such protocols.

4.1.  Top-Level Constructs

  An I-JSON message can be any JSON value.  However, there are software
  implementations, coded to the older specification [RFC4627], which
  only accept JSON objects or JSON arrays at the top level of JSON
  texts.  For maximum interoperability with such implementations,
  protocol designers SHOULD NOT use top-level JSON texts that are
  neither objects nor arrays.

4.2.  Must-Ignore Policy

  It is frequently the case that changes to protocols are required
  after they have been put in production.  Protocols that allow the
  introduction of new protocol elements in a way that does not disrupt
  the operation of existing software have proven advantageous in
  practice.

  This can be referred to as a "Must-Ignore" policy, meaning that when
  an implementation encounters a protocol element that it does not
  recognize, it should treat the rest of the protocol transaction as if
  the new element simply did not appear, and in particular, the
  implementation MUST NOT treat this as an error condition.  The
  converse "Must-Understand" policy does not tolerate the introduction



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  of new protocol elements, and while this has proven necessary in
  certain protocol designs, in general it has been found to be overly
  restrictive and brittle.

  A good way to support the use of Must-Ignore in I-JSON protocol
  designs is to require that top-level protocol elements must be JSON
  objects, and to specify that members whose names are unrecognized
  MUST be ignored.

4.3.  Time and Date Handling

  Protocols often contain data items that are designed to contain
  timestamps or time durations.  It is RECOMMENDED that all such data
  items be expressed as string values in ISO 8601 format, as specified
  in [RFC3339], with the additional restrictions that uppercase rather
  than lowercase letters be used, that the timezone be included not
  defaulted, and that optional trailing seconds be included even when
  their value is "00".  It is also RECOMMENDED that all data items
  containing time durations conform to the "duration" production in
  Appendix A of RFC 3339, with the same additional restrictions.

4.4.  Binary Data

  When it is required that an I-JSON protocol element contain arbitrary
  binary data, it is RECOMMENDED that this data be encoded in a string
  value in base64url; see Section 5 of [RFC4648].

5.  Security Considerations

  All the security considerations that apply to JSON (see RFC 7159)
  apply to I-JSON.  There are no additional security considerations
  specific to I-JSON.

  Since I-JSON forbids the use of certain JSON idioms that can lead to
  unpredictable behavior in receiving software, it may prove a more
  secure basis for Internet protocols and may be a good choice for
  protocol designers with special security needs.

6.  Normative References

  [IEEE754]  IEEE, "IEEE Standard for Floating-Point Arithmetic", IEEE
             754-2008, 2008, <http://grouper.ieee.org/groups/754/>.

  [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>.





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  [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
             Timestamps", RFC 3339, July 2002,
             <http://www.rfc-editor.org/info/rfc3339>.

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

  [RFC4627]  Crockford, D., "The application/json Media Type for
             JavaScript Object Notation (JSON)", RFC 4627, July 2006,
             <http://www.rfc-editor.org/info/rfc4627>.

  [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
             Encodings", RFC 4648, October 2006,
             <http://www.rfc-editor.org/info/rfc4648>.

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

  [UNICODE]  The Unicode Consortium, "The Unicode Standard",
             <http://www.unicode.org/versions/latest/>.

Acknowledgements

  I-JSON is entirely dependent on the design of JSON, largely due to
  Douglas Crockford.  The specifics were strongly influenced by the
  contributors to the design of RFC 7159 in the IETF JSON Working
  Group.

Author's Address

  Tim Bray (editor)
  Textuality Services

  EMail: [email protected]
  URI:   https://www.tbray.org/














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