HTTP/2 Encoded Data
draft-kerwin-http2-encoded-data-05

Network Working Group                                          M. Kerwin
Internet-Draft                                              May 29, 2015
Intended status: Experimental
Expires: November 30, 2015

                          HTTP/2 Encoded Data
                   draft-kerwin-http2-encoded-data-05

Abstract

   This document introduces new frame types for transporting gzip-
   encoded data between peers in the Hypertext Transfer Protocol Version
   2 (HTTP/2), and an associated error code for handling invalid
   encoding.

Status of This Memo

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   This Internet-Draft will expire on November 30, 2015.

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   Copyright (c) 2015 IETF Trust and the persons identified as the
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Table of Contents

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

1.  Introduction

   This document introduces a mechanism for applying gzip encoding
   [RFC1952] to data transported between two endpoints in the Hypertext
   Transfer Protocol Version 2 (HTTP/2) [RFC7540], 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 ([RFC7540],
   Section 11.2) and a new HTTP/2 error code ([RFC7540], Section 7), to
   allow the compression of data.

   Note that while compressing 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 uncompressed data.  This is particularly relevant
   when detecting malformed messages ([RFC7540], Section 8.1.2.3).

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2.1.  ACCEPT_GZIPPED_DATA

   An ACCEPT_GZIPPED_DATA frame (type code=0xTBA) is used to indicate
   the sender's ability and willingness to receive GZIPPED_DATA frames.

   ACCEPT_GZIPPED_DATA always applies to a connection, never a single
   stream.  The stream identifier for an ACCEPT_GZIPPED_DATA frame MUST
   be zero (0x0).  If an endpoint receives an ACCEPT_GZIPPED_DATA frame
   whose stream identifier field is anything other than 0x0, the
   endpoint MUST respond with a connection error (([RFC7540],
   Section 5.4.1) of type PROTOCOL_ERROR.

   The payload length of an ACCEPT_GZIPPED_DATA frame MUST be zero.  An
   endpoint that receives an ACCEPT_GZIPPED_DATA frame a length other
   than zero MUST treat this as a connection error ([RFC7540],
   Section 5.4.1) of type PROTOCOL_ERROR.

   The ACCEPT_GZIPPED_DATA frame defines the following flag:

   o  DISABLE (0x1): When set, bit 0 indicates that this endpoint is not
      willing or able to receive GZIPPED_DATA frames.

   An endpoint may advertise support for GZIPPED_DATA frames and later
   decide that it no longer supports them.  After sending an
   ACCEPT_GZIPPED_DATA with the DISABLE flag set, the endpoint SHOULD
   continue to accept GZIPPED_DATA frames for a reasonable amount of
   time to account for frames that are already in flight.

   The ACCEPT_GZIPPED_DATA frame is not subject to flow control.

2.2.  GZIPPED_DATA

   GZIPPED_DATA frames (type code=0xTBA) are semantically identical to
   DATA frames ([RFC7540], Section 6.1), but their payload is encoded
   using gzip compression.  Gzip compression is an LZ77 coding with a 32
   bit CRC that is commonly produced by the gzip file compression
   program [RFC1952].  Significantly, GZIPPED_DATA frames are subject to
   flow control ([RFC7540], Section 5.2).

   Any compression or decompression context for a GZIPPED_DATA frame is
   unique to that frame.

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     +---------------+
     |Pad Length? (8)|
     +---------------+-----------------------------------------------+
     |                            Data (*)                         ...
     +---------------------------------------------------------------+
     |                           Padding (*)                       ...
     +---------------------------------------------------------------+

                        GZIPPED_DATA Frame Payload

   The GZIPPED_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  Data: Encoded application data.  The amount of compressed 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 GZIPPED_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 ([RFC7540], Section 5.1).

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

   A GZIPPED_DATA frame MUST NOT be sent on a connection before
   receiving an ACCEPT_GZIPPED_DATA frame.

   An intermediary, on receiving a GZIPPED_DATA frame, MAY decode the
   data and forward it to its downstream peer in one or more DATA
   frames.  If the downstream peer has not advertised support for
   GZIPPED_DATA frames (e.g. by sending an ACCEPT_GZIPPED_DATA frame)
   the intermediary MUST decode the data before forwarding it.

   If an endpoint detects that the payload of a GZIPPED_DATA frame is
   not encoded correctly, for example with a mismatched checksum, the
   endpoint MUST treat this as a stream error (see [RFC7540],
   Section 5.4.2) of type DATA_ENCODING_ERROR (Section 2.3).  The

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   endpoint MAY then choose to immediately send an ACCEPT_GZIPPED_DATA
   frame with the DISABLE flag set.

   If an intermediary propagates a GZIPPED_DATA frame from the source
   peer to the destination peer without modifying the payload or its
   encoding, and receives a DATA_ENCODING_ERROR from the receiving peer,
   it SHOULD pass the error on to the source peer.

   GZIPPED_DATA frames MUST be associated with a stream.  If a
   GZIPPED_DATA frame is received whose stream identifier field is 0x0,
   the recipient MUST respond with a connection error ([RFC7540],
   Section 5.4.1) of type PROTOCOL_ERROR.

   GZIPPED_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 GZIPPED_DATA frame payload is included in flow control,
   including the Pad Length and Padding fields if present.  If a
   GZIPPED_DATA frame is received whose stream is not in "open" or "half
   closed (local)" state, the recipient MUST respond with a stream error
   ([RFC7540], Section 5.4.2) of type STREAM_CLOSED.

   The total number of padding octets is determined by the value of the
   Pad Length field.  If the length of the padding is greater than the
   length of the remainder of the frame payload, the recipient MUST
   treat this as a connection error ([RFC7540], Section 5.4.1) of type
   PROTOCOL_ERROR.

   Note: A frame can be increased in size by one octet by including a
   Pad Length field with a value of zero.

   Padding is a security feature; see Section 10.7 of [RFC7540].

2.3.  DATA_ENCODING_ERROR

   The following new error code is defined:

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

3.  Fragmentation

   Traversing a network segment with small frame size limits introduces
   the risk of fragmenting an encoded stream.

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4.  Security Considerations

   Further to the Use of Compression in HTTP/2 ([RFC7540],
   Section 10.6), intermediaries MUST NOT apply compression to DATA
   frames, or alter the compression of GZIPPED_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 ([RFC7540],
   Section 11.2).  The entries in the following table are registered by
   this document.

               +---------------------+------+-------------+
               | Frame Type          | Code | Section     |
               +---------------------+------+-------------+
               | ACCEPT_GZIPPED_DATA | TBD  | Section 2.1 |
               | GZIPPED_DATA        | TBD  | Section 2.2 |
               +---------------------+------+-------------+

5.2.  HTTP/2 Error Code Registry Update

   This document updates the "HTTP/2 Error Code" registry ([RFC7540],
   Section 11.4).  The entries in the following table are registered by
   this document.

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

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6.  Acknowledgements

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

7.  References

7.1.  Normative References

   [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.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer
              Protocol Version 2 (HTTP/2)", RFC 7540, May 2015.

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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