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Network Working Group                                          M. Kerwin
Internet-Draft
Intended status: Standards Track                           July 22, 2014
Expires: January 23, 2015


                          HTTP/2 Encoded Data
                   draft-kerwin-http2-encoded-data-01

Abstract

   This document introduces new frame types for transporting encoded
   data in HTTP/2, and an associated error code.

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
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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 January 23, 2015.

Copyright Notice

   Copyright (c) 2014 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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   described in the Simplified BSD License.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Additions to HTTP/2 . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  ACCEPT_ENCODED_DATA . . . . . . . . . . . . . . . . . . .   3
     2.2.  ENCODED_DATA  . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  DATA_ENCODING_ERROR . . . . . . . . . . . . . . . . . . .   6
   3.  Encoding Schemes  . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  HTTP/2 Frame Type Registry Update . . . . . . . . . . . .   7
     5.2.  HTTP/2 Error Code Registry Update . . . . . . . . . . . .   7
     5.3.  HTTP/2 Encoding Schemes Registry  . . . . . . . . . . . .   8
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9
































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1.  Introduction

   This document introduces a mechanism for applying encoding,
   particularly compression, to data transported between two HTTP/2
   endpoints, analogous to Transfer-Encoding in HTTP/1.1 [RFC7230].

1.1.  Notational Conventions

   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.  Additions to HTTP/2

   This document introduces two new HTTP/2 frame types
   ([I-D.ietf-httpbis-http2], Section 11.2), and a new error code
   ([I-D.ietf-httpbis-http2], Section 7).

   Note that while encoding some or all data in a stream might affect
   the total length of the corresponding HTTP message body, the
   "content-length" header, if present, should continue to reflect the
   total length of the unencoded data.  This is particularly relevant
   when detecting malformed messages ([I-D.ietf-httpbis-http2],
   Section 8.1.2.5).

2.1.  ACCEPT_ENCODED_DATA

   An "ACCEPT_ENCODED_DATA" frame (type code=0xTBA) is used to indicate
   the sender's ability and willingness to receive "ENCODED_DATA" frames
   that are encoded using the schemes identified in its payload.

   The payload length of an "ACCEPT_ENCODED_DATA" frame MUST be an exact
   multiple of 16 bits (2 bytes).  An endpoint that receives an
   "ACCEPT_ENCODED_DATA" frame with an odd length MUST treat this as a
   connection error ([I-D.ietf-httpbis-http2], Section 5.4.1) of type
   "PROTOCOL_ERROR".

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Encoding (8)  |   Rank (8)    | ...
   +---------------+---------------+-------------------------------+

                     ACCEPT_ENCODED_DATA Frame Payload

   The "ACCEPT_ENCODED_DATA" frame contains zero or more tuples
   comprising the following fields:




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   o  Encoding: An 8-bit identifier which identifies the encoding being
      advertised (see Section 3).

   o  Rank: An 8-bit integer value.

   The rank fulfils the same role as in the HTTP/1.1 TE header
   ([RFC7230] Section 4.3).  The rank value is an integer in the range 0
   through 255, where 1 is the least preferred and 255 is the most
   preferred; a value of 0 means "not acceptable".

   An endpoint that receives an "ACCEPT_ENCODED_DATA" frame containing
   an {encoding,rank} tuple with an unknown or unsupported encoding
   identifier MUST ignore that tuple.

   Each "ACCEPT_ENCODED_DATA" frame fully replaces the set of tuples
   sent in a previous frame; if an encoding identifier is omitted from a
   subsequent "ACCEPT_ENCODED_DATA" frame it is deemed "not acceptable".

   An endpoint may advertise support for an encoding scheme and later
   decide that it no longer supports that scheme.  After sending an
   "ACCEPT_ENCODED_DATA" that omits the encoding identifier in question,
   or includes it with a rank of 0, the endpoint SHOULD continue to
   accept "ENCODED_DATA" frames using that scheme for a reasonable
   amount of time to account for encoded frames that are already in
   flight.

   The "ACCEPT_ENCODED_DATA" frame does not define any flags, and is not
   subject to flow control.

2.2.  ENCODED_DATA

   "ENCODED_DATA" frames (type code=0xTBA) are semantically identical to
   "DATA" frames ([I-D.ietf-httpbis-http2], Section 6.1), but have an
   encoding applied to their payload.  Significantly, "ENCODED_DATA"
   frames are subject to flow control ([I-D.ietf-httpbis-http2],
   Section 5.2).

   Any encoding or decoding context for an "ENCODED_DATA" frame is
   unique to that frame.












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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Pad Length? (8)|
   +---------------+
   | Encoding (8)  |
   +---------------+-----------------------------------------------+
   |                            Data (*)                         ...
   +---------------------------------------------------------------+
   |                           Padding (*)                       ...
   +---------------------------------------------------------------+

                        ENCODED_DATA Frame Payload

   The "ENCODED_DATA" frame contains the following fields:

   o  Pad Length: An 8-bit field containing the length of the frame
      padding in units of octets.  This field is optional and is only
      present if the PADDED flag is set.

   o  Encoding: An 8-bit identifier which identifies the encoding that
      has been applied to the Data field (see Section 3).

   o  Data: Encoded application data.  The amount of encoded data is the
      remainder of the frame payload after subtracting the length of the
      other fields that are present.

   o  Padding: Padding octets that contain no application semantic
      value.  Padding octets MUST be set to zero when sending and
      ignored when receiving.

   The "ENCODED_DATA" frame defines the following flags:

   o  "END_STREAM" (0x1): Bit 1 being set indicates that this frame is
      the last that the endpoint will send for the identified stream.
      Setting this flag causes the stream to enter one of the "half
      closed" states or the "closed" state ([I-D.ietf-httpbis-http2],
      Section 5.1).

   o  "END_SEGMENT" (0x2): Bit 2 being set indicates that this frame is
      the last for the current segment.  Intermediaries MUST NOT
      coalesce frames across a segment boundary and MUST preserve
      segment boundaries when forwarding frames.

   o  "PADDED" (0x8): Bit 4 being set indicates that the Pad Length
      field is present.





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   On receiving an "ENCODED_DATA" frame, an intermediary MAY decode the
   data and forward it in one or more "DATA" frames.  If the downstream
   peer does not support the encoding scheme used in the received frame,
   as advertised in an "ACCEPT_ENCODED_DATA" frame, the intermediary
   MUST decode the data and either: forward it in one or more DATA
   frames, or encode it with a scheme supported by the downstream peer
   and forward it in one or more "ENCODED_DATA" frames.

   An "ENCODED_DATA" frame MUST NOT be sent on a connection before
   receiving an "ACCEPT_ENCODED_DATA" frame.  A sender MUST NOT apply an
   encoding that has not first been advertised by the peer in an
   "ACCEPT_ENCODED_DATA" frame, or was advertised with a rank of 0.
   Endpoints that receive a frame with an encoding they do not recognise
   or support MUST treat this as a connection error of type
   "PROTOCOL_ERROR".

   If an endpoint detects that the payload of an "ENCODED_DATA" frame is
   incorrectly encoded it MUST treat this as a stream error (see
   [I-D.ietf-httpbis-http2], Section 5.4.2) of type
   "DATA_ENCODING_ERROR" (Section 2.3).

   "ENCODED_DATA" frames are subject to flow control and can only be
   sent when a stream is in the "open" or "half closed (remote)" states.
   The entire "ENCODED_DATA" frame payload is included in flow control,
   including the encoded data, and Pad Length and Padding fields if
   present.  If an "ENCODED_DATA" frame is received whose stream is not
   in "open" or "half closed (local)" state, the recipient MUST respond
   with a stream error ([I-D.ietf-httpbis-http2], Section 5.4.2) of type
   STREAM_CLOSED.

2.3.  DATA_ENCODING_ERROR

   The following new error code is defined:

   o  DATA_ENCODING_ERROR (0xTBA): The endpoint detected that its peer
      sent an "ENCODED_DATA" frame with an invalid encoding.

3.  Encoding Schemes

   The following encoding schemes are defined:

   o  "ENCODING_COMPRESS" (1): The "compress" coding is an adaptive
      Lempel-Ziv-Welch (LZW) coding [Welch] that is commonly produced by
      the UNIX file compression program "compress".

   o  "ENCODING_DEFLATE" (2): The "deflate" coding is a "zlib" data
      format [RFC1950] containing a "deflate" compressed data stream




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      [RFC1951] that uses a combination of the Lempel-Ziv (LZ77)
      compression algorithm and Huffman coding.

   o  "ENCODING_GZIP" (3): The "gzip" coding is an LZ77 coding with a 32
      bit CRC that is commonly produced by the gzip file compression
      program [RFC1952].

4.  Security Considerations
   Further to the Use of Compression in HTTP/2
   ([I-D.ietf-httpbis-http2], Section 10.6), intermediaries MUST NOT
   apply compression to DATA frames, or alter the compression of
   "ENCODED_DATA" frames, other than decompressing, unless additional
   information is available that allows the intermediary to identify the
   source of data.  In particular, frames that are not compressed cannot
   be compressed, and frames that are separately compressed cannot be
   merged into a single compressed frame.

5.  IANA Considerations

   This document updates the registries for frame types and error codes
   in the "Hypertext Transfer Protocol (HTTP) 2 Parameters" section.
   This document also establishes a new registry for HTTP/2 encoding
   scheme codes.  This new registry is entered into the "Hypertext
   Transfer Protocol (HTTP) 2 Parameters" section.

5.1.  HTTP/2 Frame Type Registry Update

   This document updates the "HTTP/2 Frame Type" registry
   ([I-D.ietf-httpbis-http2], Section 11.2).  The entries in the
   following table are registered by this document.

               +---------------------+------+-------------+
               | Frame Type          | Code | Section     |
               +---------------------+------+-------------+
               | ACCPET_ENCODED_DATA | TBD  | Section 2.1 |
               | ENCODED_DATA        | TBD  | Section 2.2 |
               +---------------------+------+-------------+

5.2.  HTTP/2 Error Code Registry Update

   This document updates the "HTTP/2 Error Code" registry
   ([I-D.ietf-httpbis-http2], Section 11.4).  The entries in the
   following table are registered by this document.









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   +-----------------------+-------+-----------------+-----------------+
   | Name                  | Code  | Description     | Specification   |
   +-----------------------+-------+-----------------+-----------------+
   | DATA_ENCODING_ERROR   | TBD   | Invalid         | Section 2.3     |
   |                       |       | encoding        |                 |
   |                       |       | detected        |                 |
   +-----------------------+-------+-----------------+-----------------+

5.3.  HTTP/2 Encoding Schemes Registry

   This document establishes a registry for encoding scheme codes.  The
   "HTTP/2 Encoding Schemes" registry manages an 8-bit space.  The "HTTP
   /2 Encoding Schemes" registry operates under either of the "IETF
   Review" or "IESG Approval" policies [RFC5226] for values between 0x00
   and 0xef, with values between 0xf0 and 0xff being reserved for
   experimental use.

   New entries in this registry require the following information:

   o  Frame Type: A name or label for the encoding scheme.

   o  Code: The 8-bit code assigned to the encoding scheme.

   o  Specification: A reference to a specification that includes a
      description of the encoding scheme.

   An initial set of encoding scheme code registrations can be found in
   Section 3.

6.  Acknowledgements

   Thanks to Keith Morgan for his advice, input, and editorial
   contributions.

7.  References

7.1.  Normative References

   [I-D.ietf-httpbis-http2]
              Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer
              Protocol version 2", draft-ietf-httpbis-http2-13 (work in
              progress), June 2014.

   [RFC1950]  Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data Format
              Specification version 3.3", RFC 1950, May 1996.

   [RFC1951]  Deutsch, P., "DEFLATE Compressed Data Format Specification
              version 1.3", RFC 1951, May 1996.



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   [RFC1952]  Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G.
              Randers-Pehrson, "GZIP file format specification version
              4.3", RFC 1952, May 1996.

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

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.
   [Welch]    Welch, T., "A Technique for High-Performance Data
              Compression", IEEE Computer 17(6), June 1984.

7.2.  Informative References

   [RFC7230]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Message Syntax and Routing", RFC 7230, June
              2014.

Author's Address

   Matthew Kerwin

   Email: matthew@kerwin.net.au
   URI:   http://matthew.kerwin.net.au/


























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