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rfc:rfc6839

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.

Hansen & Melnikov Informational [Page 1] RFC 6839 Additional Media Type Suffixes January 2013

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

Hansen & Melnikov Informational [Page 2] RFC 6839 Additional Media Type Suffixes January 2013

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.

Hansen & Melnikov Informational [Page 3] RFC 6839 Additional Media Type Suffixes January 2013

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)

Hansen & Melnikov Informational [Page 4] RFC 6839 Additional Media Type Suffixes January 2013

 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.

Hansen & Melnikov Informational [Page 5] RFC 6839 Additional Media Type Suffixes January 2013

    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.

Hansen & Melnikov Informational [Page 6] RFC 6839 Additional Media Type Suffixes January 2013

       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

Hansen & Melnikov Informational [Page 7] RFC 6839 Additional Media Type Suffixes January 2013

 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)

Hansen & Melnikov Informational [Page 9] RFC 6839 Additional Media Type Suffixes January 2013

 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

Hansen & Melnikov Informational [Page 10] RFC 6839 Additional Media Type Suffixes January 2013

 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.)

Hansen & Melnikov Informational [Page 11] RFC 6839 Additional Media Type Suffixes January 2013

    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.

Hansen & Melnikov Informational [Page 12] RFC 6839 Additional Media Type Suffixes January 2013

 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.

Hansen & Melnikov Informational [Page 13] RFC 6839 Additional Media Type Suffixes January 2013

 [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

Hansen & Melnikov Informational [Page 14]

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