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Versions: (draft-bray-i-json) 00 01 02 03 04 05 06 RFC 7493

Network Working Group                                       T. Bray, Ed.
Internet-Draft                                       Textuality Services
Intended status: Standards Track                        January 27, 2015
Expires: July 31, 2015


                       The I-JSON Message Format
                       draft-ietf-json-i-json-06

Abstract

   I-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 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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 July 31, 2015.

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
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   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.  Protocol-design Recommendations . . . . . . . . . . . . . . .   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.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   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 which 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 which
   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 which 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 which identify Surrogates or
   Noncharacters [UNICODE] (Section 2.4).

   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 which implements IEEE 754-2008 binary64 (double precision)
   numbers [IEEE754] is generally available and widely used.
   Implementations which 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 which 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 which 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.

   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




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   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 which do not
   conform to the requirements in this document for I-JSON messages.
   Protocols that use I-JSON message 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 which 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.  Protocol-design Recommendations

   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 [RFC4627] specification, 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 which 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 which 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 which 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 MUST NOT
   treat this as an error condition.  The converse "Must-Understand"
   policy does not tolerate the introduction 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.



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   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 which 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 RFC3339, 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.  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 on the IETF JSON Working
   Group.

6.  Security Considerations

   All the security considerations which 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.

7.  Normative References

   [IEEE754]  IEEE, "IEEE Standard for Floating-Point Arithmetic", 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.



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   [RFC3339]  Klyne, G., Ed. and C. Newman, "Date and Time on the
              Internet: Timestamps", RFC 3339, July 2002.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC7159]  Bray, T., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, March 2014.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard", 2003-,
              <http://www.unicode.org/versions/latest/>.

              Note that this reference is to the latest version of
              Unicode, rather than to a specific release.  It is not
              expected that future changes in the UNICODE specification
              will affect the referenced classifications.

Author's Address

   Tim Bray (editor)
   Textuality Services

   Email: tbray@textuality.com
   URI:   https://www.tbray.org/





















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