The I-JSON Message Format
RFC 7493

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

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