Additional Media Type Structured Syntax Suffixes
RFC 6839

Internet Engineering Task Force (IETF)                         T. Hansen
Request for Comments: 6839                             AT&T Laboratories
Updates: 3023                                                A. Melnikov
Category: Informational                                        Isode Ltd
ISSN: 2070-1721                                             January 2013

            Additional Media Type Structured Syntax Suffixes

Abstract

   A content media type name sometimes includes partitioned meta-
   information distinguished by a structured syntax to permit noting an
   attribute of the media as a suffix to the name.  This document
   defines several structured syntax suffixes for use with media type
   registrations.  In particular, it defines and registers the "+json",
   "+ber", "+der", "+fastinfoset", "+wbxml" and "+zip" structured syntax
   suffixes, and provides a media type structured syntax suffix
   registration form for the "+xml" structured syntax suffix.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see 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/rfc6839.

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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.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  When to Use These Structured Syntax Suffixes . . . . . . . . .  3
   3.  Initial Structured Syntax Suffix Definitions . . . . . . . . .  4
     3.1.  The +json Structured Syntax Suffix . . . . . . . . . . . .  4
     3.2.  The +ber Structured Syntax Suffix  . . . . . . . . . . . .  5
     3.3.  The +der Structured Syntax Suffix  . . . . . . . . . . . .  6
     3.4.  The +fastinfoset Structured Syntax Suffix  . . . . . . . .  7
     3.5.  The +wbxml Structured Syntax Suffix  . . . . . . . . . . .  9
     3.6.  The +zip Structured Syntax Suffix  . . . . . . . . . . . . 10
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
     4.1.  The +xml Structured Syntax Suffix  . . . . . . . . . . . . 11
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 13

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1.  Introduction

   [RFC3023] created the +xml suffix convention that can be used when
   defining names for media types whose representation uses XML
   underneath.  That is, they could have been successfully parsed as if
   the media type had been application/xml in addition to their being
   parsed as their media type that is using the +xml suffix.  [RFC6838]
   defines the media type "Structured Syntax Suffix Registry" to be used
   for such structured syntax suffixes.

   A variety of structured syntax suffixes have already been used in
   some media type registrations, in particular "+json", "+der",
   "+fastinfoset", and "+wbxml".  This document defines and registers
   these structured syntax suffixes in the Structured Syntax Suffix
   Registry, along with "+ber" and "+zip".  In addition, this document
   updates [RFC3023] to formally register the "+xml" structured syntax
   suffix according to the procedure defined in [RFC6838].

   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].

2.  When to Use These Structured Syntax Suffixes

   Each of the structured syntax suffixes defined in this document is
   appropriate for use when the media type identifies the semantics of
   the protocol payload.  That is, knowing the semantics of the specific
   media type provides for more specific processing of the content than
   that afforded by generic processing of the underlying representation.

   At the same time, using the suffix allows receivers of the media
   types to do generic processing of the underlying representation in
   cases where

      they do not need to perform special handling of the particular
      semantics of the exact media type, and

      there is no special knowledge needed by such a generic processor
      in order to parse that underlying representation other than what
      would be needed to parse any example of that underlying
      representation.

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3.  Initial Structured Syntax Suffix Definitions

3.1.  The +json Structured Syntax Suffix

   [RFC4627] defines the "application/json" media type.  The suffix
   "+json" MAY be used with any media type whose representation follows
   that established for "application/json".  The media type structured
   syntax suffix registration form follows.  See [RFC6838] for
   definitions of each of the registration form headings.

   Name:  JavaScript Object Notation (JSON)

   +suffix:  +json

   References:  [RFC4627]

   Encoding considerations:

      Per [RFC4627], JSON is allowed to be represented using UTF-8,
      UTF-16, or UTF-32.  When JSON is written in UTF-8, JSON is 8bit
      compatible ([RFC2045]).  When JSON is written in UTF-16 or UTF-32,
      JSON is binary ([RFC2045]).

   Fragment identifier considerations:

      The syntax and semantics of fragment identifiers specified for
      +json SHOULD be as specified for "application/json".  (At
      publication of this document, there is no fragment identification
      syntax defined for "application/json".)

      The syntax and semantics for fragment identifiers for a specific
      "xxx/yyy+json" SHOULD be processed as follows:

      For cases defined in +json, where the fragment identifier resolves
      per the +json rules, then process as specified in +json.

         For cases defined in +json, where the fragment identifier does
         not resolve per the +json rules, then process as specified in
         "xxx/yyy+json".

         For cases not defined in +json, then process as specified in
         "xxx/yyy+json".

   Interoperability considerations:  n/a

   Security considerations:  See [RFC4627]

   Contact:  Apps Area Working Group (apps-discuss@ietf.org)

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   Author/Change controller:

      The Apps Area Working Group.  IESG has change control over this
      registration.

3.2.  The +ber Structured Syntax Suffix

   The ITU defined the Basic Encoding Rules (BER) transfer syntax in
   [ITU.X690.2008].  The suffix "+ber" MAY be used with any media type
   whose representation follows the BER transfer syntax.  (The Expert
   Reviewer for media type structured syntax suffix registrations ought
   to be aware of the relationship between BER and DER to aid in
   selecting the proper suffix.)  The media type structured syntax
   suffix registration form for +ber follows:

   Name:  Basic Encoding Rules (BER) transfer syntax

   +suffix:  +ber

   References:  [ITU.X690.2008]

   Encoding considerations:  BER is a binary encoding.

   Fragment identifier considerations:

      At publication of this document, there is no fragment
      identification syntax defined for +ber.

      The syntax and semantics for fragment identifiers for a specific
      "xxx/yyy+ber" SHOULD be processed as follows:

         For cases defined in +ber, where the fragment identifier
         resolves per the +ber rules, then process as specified in +ber.

         For cases defined in +ber, where the fragment identifier does
         not resolve per the +ber rules, then process as specified in
         "xxx/yyy+ber".

         For cases not defined in +ber, then process as specified in
         "xxx/yyy+ber".

   Interoperability considerations:  n/a

   Security considerations:

      Each individual media type registered with a +ber suffix can have
      additional security considerations.

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      BER has a type-length-value structure, and it is easy to construct
      malicious content with invalid length fields that can cause buffer
      overrun conditions.

      BER allows for arbitrary levels of nesting, which may make it
      possible to construct malicious content that will cause a stack
      overflow.

      Interpreters of the BER structures should be aware of these issues
      and should take appropriate measures to guard against buffer
      overflows and stack overruns in particular and malicious content
      in general.

   Contact:  Apps Area Working Group (apps-discuss@ietf.org)

   Author/Change controller:

      The Apps Area Working Group.  IESG has change control over this
      registration.

3.3.  The +der Structured Syntax Suffix

   The ITU defined the Distinguished Encoding Rules (DER) transfer
   syntax in [ITU.X690.2008].  The suffix "+der" MAY be used with any
   media type whose representation follows the DER transfer syntax.
   (The Expert Reviewer for media type structured syntax suffix
   registrations ought to be aware of the relationship between BER and
   DER to aid in selecting the proper suffix.)  The media type
   structured syntax suffix registration form for +der follows:

   Name:  Distinguished Encoding Rules (DER) transfer syntax

   +suffix:  +der

   References:  [ITU.X690.2008]

   Encoding considerations:  DER is a binary encoding.

   Fragment identifier considerations:

      At publication of this document, there is no fragment
      identification syntax defined for +der.

      The syntax and semantics for fragment identifiers for a specific
      "xxx/yyy+der" SHOULD be processed as follows:

         For cases defined in +der, where the fragment identifier
         resolves per the +der rules, then process as specified in +der.

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         For cases defined in +der, where the fragment identifier does
         not resolve per the +der rules, then process as specified in
         "xxx/yyy+der".

         For cases not defined in +der, then process as specified in
         "xxx/yyy+der".

   Interoperability considerations:  n/a

   Security considerations:

      Each individual media type registered with a +der suffix can have
      additional security considerations.

      DER has a type-length-value structure, and it is easy to construct
      malicious content with invalid length fields that can cause buffer
      overrun conditions.

      DER allows for arbitrary levels of nesting, which may make it
      possible to construct malicious content that will cause a stack
      overflow.

      Interpreters of the DER structures should be aware of these issues
      and should take appropriate measures to guard against buffer
      overflows and stack overruns in particular and malicious content
      in general.

   Contact:  Apps Area Working Group (apps-discuss@ietf.org)

   Author/Change controller:

      The Apps Area Working Group.  IESG has change control over this
      registration.

3.4.  The +fastinfoset Structured Syntax Suffix

   The ITU defined the Fast Infoset document format as a binary
   representation of the XML Information Set in [ITU.X891.2005].  These
   documents further define the "application/fastinfoset" media type.
   The suffix "+fastinfoset" MAY be used with any media type whose
   representation follows that established for "application/
   fastinfoset".  The media type structured syntax suffix registration
   form follows:

   Name:  Fast Infoset document format

   +suffix:  +fastinfoset

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   References:  [ITU.X891.2005]

   Encoding considerations:

      Fast Infoset is a binary encoding.  The binary, quoted-printable,
      and base64 content-transfer-encodings are suitable for use with
      Fast Infoset.

   Fragment identifier considerations:

      The syntax and semantics of fragment identifiers specified for
      +fastinfoset SHOULD be as specified for "application/fastinfoset".
      (At publication of this document, there is no fragment
      identification syntax defined for "application/fastinfoset".)

      The syntax and semantics for fragment identifiers for a specific
      "xxx/ yyy+fastinfoset" SHOULD be processed as follows:

         For cases defined in +fastinfoset, where the fragment
         identifier resolves per the +fastinfoset rules, then process as
         specified in +fastinfoset.

         For cases defined in +fastinfoset, where the fragment
         identifier does not resolve per the +fastinfoset rules, then
         process as specified in "xxx/yyy+fastinfoset".

         For cases not defined in +fastinfoset, then process as
         specified in "xxx/ yyy+fastinfoset".

   Interoperability considerations:  n/a

   Security considerations:

      There are no security considerations inherent in Fast Infoset.
      Each individual media type registered with a +fastinfoset suffix
      can have additional security considerations.

   Contact:  Apps Area Working Group (apps-discuss@ietf.org)

   Author/Change controller:

      The Apps Area Working Group.  IESG has change control over this
      registration.

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3.5.  The +wbxml Structured Syntax Suffix

   The Wireless Application Protocol (WAP) Forum has defined the WAP
   Binary XML (WBXML) document format as a binary representation of XML
   in [WBXML].  This document further defines the "application/
   vnd.wap.wbxml" media type.  The suffix "+wbxml" MAY be used with any
   media type whose representation follows that established for
   "application/vnd.wap.wbxml".  The media type structured syntax suffix
   registration form follows:

   Name:  WAP Binary XML (WBXML) document format

   +suffix:  +wbxml

   References:  [WBXML]

   Encoding considerations:  WBXML is a binary encoding.

   Fragment identifier considerations:

      The syntax and semantics of fragment identifiers specified for
      +wbxml SHOULD be as specified for "application/vnd.wap.wbxml".
      (At publication of this document, there is no fragment
      identification syntax defined for "application/vnd.wap.wbxml".)

      The syntax and semantics for fragment identifiers for a specific
      "xxx/yyy+wbxml" SHOULD be processed as follows:

         For cases defined in +wbxml, where the fragment identifier
         resolves per the +wbxml rules, then process as specified in
         +wbxml.

         For cases defined in +wbxml, where the fragment identifier does
         not resolve per the +wbxml rules, then process as specified in
         "xxx/yyy+wbxml".

         For cases not defined in +wbxml, then process as specified in
         "xxx/yyy+wbxml".

   Interoperability considerations:  n/a

   Security considerations:

      There are no security considerations inherent in WBXML.  Each
      individual media type registered with a +wbxml suffix can have
      additional security considerations.

   Contact:  Apps Area Working Group (apps-discuss@ietf.org)

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   Author/Change controller:

      The Apps Area Working Group.  IESG has change control over this
      registration.

3.6.  The +zip Structured Syntax Suffix

   The ZIP format is a public domain, cross-platform, interoperable file
   storage and transfer format, originally defined by PKWARE, Inc.; it
   supports compression and encryption and is used as the underlying
   representation by a variety of file formats.  The media type
   "application/zip" has been registered for such files.  The suffix
   "+zip" MAY be used with any media type whose representation follows
   that established for "application/zip".  The media type structured
   syntax suffix registration form follows:

   Name:  ZIP file storage and transfer format

   +suffix:  +zip

   References:  [ZIP]

   Encoding considerations:  ZIP is a binary encoding.

   Fragment identifier considerations:

      The syntax and semantics of fragment identifiers specified for
      +zip SHOULD be as specified for "application/zip".  (At
      publication of this document, there is no fragment identification
      syntax defined for "application/zip".)

      The syntax and semantics for fragment identifiers for a specific
      "xxx/yyy+zip" SHOULD be processed as follows:

         For cases defined in +zip, where the fragment identifier
         resolves per the +zip rules, then process as specified in +zip.

         For cases defined in +zip, where the fragment identifier does
         not resolve per the +zip rules, then process as specified in
         "xxx/yyy+zip".

         For cases not defined in +zip, then process as specified in
         "xxx/yyy+zip".

   Interoperability considerations:  n/a

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   Security considerations:

      IP files support two forms of encryption: Strong Encryption and
      AES 128-bit, 192-bit, and 256-bit encryption; see the
      specification for further details.  Each individual media type
      registered with a +zip suffix can have additional security
      considerations.

   Contact:  Apps Area Working Group (apps-discuss@ietf.org)

   Author/Change controller:  The Apps Area Working Group.  IESG has
      change control over this registration.

4.  IANA Considerations

   See the media type structured syntax suffix registration forms in
   Sections 3.1 - 3.6.

4.1.  The +xml Structured Syntax Suffix

   The following structured syntax suffix registration for "+xml" shall
   be used to reflect the information found in [RFC3023], with the
   addition of fragment identifier considerations.  (Note that [RFC3023]
   is in the process of being updated by [XML-MEDIATYPES].)

   Name:  Extensible Markup Language (XML)

   +suffix:  +xml

   References:  [RFC3023]

   Encoding considerations:

      Per [RFC3023], XML is allowed to be represented using both 7-bit
      and 8-bit encodings.  When XML is written in UTF-8, XML is 8bit
      compatible ([RFC2045]).  When XML is written in UTF-16 or UTF-32,
      XML is binary ([RFC2045]).

   Fragment identifier considerations:

      The syntax and semantics of fragment identifiers specified for
      +xml SHOULD be as specified for "application/xml".  (At
      publication of this document, the fragment identification syntax
      considerations for "application/xml" are defined in [RFC3023],
      Sections 5 and 7.)

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      The syntax and semantics for fragment identifiers for a specific
      "xxx/yyy+xml" SHOULD be processed as follows:

         For cases defined in +xml, where the fragment identifier
         resolves per the +xml rules, then process as specified in +xml.

         For cases defined in +xml, where the fragment identifier does
         not resolve per the +xml rules, then process as specified in
         "xxx/yyy+xml".

         For cases not defined in +xml, then process as specified in
         "xxx/yyy+xml".

   Interoperability considerations:  See [RFC3023].

   Security considerations:  See [RFC3023]

   Contact:  Apps Area Working Group (apps-discuss@ietf.org)

   Author/Change controller:

      The Apps Area Working Group.  IESG has change control over this
      registration.

5.  Security Considerations

   See the Security Considerations sections found in the media type
   structured syntax suffix registration forms from Sections 3 and 4.

   When updating a +<suffix> registration, care should be taken to
   review all previously-registered xxx/yyy+<suffix> media types as to
   whether they might be affected by the updated +<suffix> registration.
   Because the generic fragment identifier processing rules take
   precedence over media-type-specific rules, introducing new or
   changing existing definitions may break the existing registrations of
   specific media types, as well as particular implementations of
   applications that process affected media types.  Such changes can
   introduce interoperability and security issues.

   When updating the fragment identifier processing rules for a specific
   xxx/yyy+<suffix> media type, care should be taken to review the
   generic fragment identifier processing rules for the +<suffix>
   registration and not introduce any conflicts.  Because the generic
   fragment identifier processing rules take precedence over media-type-
   specific rules, such conflicting processing requirements should be
   ignored by an implementation, but such conflicts can introduce
   interoperability and security issues.

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   Note that [FRAGID-BP] provides additional advice to designers of
   fragment identifier rules for media type suffixes and specific media
   types.

6.  References

6.1.  Normative References

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

   [ITU.X690.2008]
              International Telecommunications Union, "Recommendation
              ITU-T X.690 | ISO/IEC 8825-1 (2008), ASN.1 encoding rules:
              Specification of basic encoding Rules (BER), Canonical
              encoding rules (CER) and Distinguished encoding rules
              (DER)", ITU-T Recommendation X.690, November 2008.

   [ITU.X891.2005]
              International Telecommunications Union, "Recommendation
              ITU-T X.891 | ISO/IEC 24824-1 (2007), Generic applications
              of ASN.1: Fast infoset", ITU-T Recommendation X.891,
              May 2005.

   [WBXML]    Open Mobile Alliance, "Binary XML Content Format
              Specification", OMA Wireless Access Protocol WAP-192-
              WBXML-20010725-a, July 2001.

   [ZIP]      PKWARE, Inc., "APPNOTE.TXT - .ZIP File Format
              Specification", PKWARE .ZIP File Format Specification -
              Version 6.3.2, September 2007.

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media
              Types", RFC 3023, January 2001.

6.2.  Informative References

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, January 2013.

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   [FRAGID-BP]
              Tennison, J., "Best Practices for Fragment Identifiers and
              Media Type Definitions", July 2012,
              <http://www.w3.org/TR/fragid-best-practices/>.

   [XML-MEDIATYPES]
              Lilley, C., Makoto, M., Melnikov, A., and H. Thompson,
              "XML Media Types", Work in Progress, November 2012.

Authors' Addresses

   Tony Hansen
   AT&T Laboratories
   200 Laurel Ave. South
   Middletown, NJ  07748
   USA

   EMail: tony+sss@maillennium.att.com

   Alexey Melnikov
   Isode Ltd
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   EMail: Alexey.Melnikov@isode.com

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