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Network Working Group                                          M. Kerwin
Internet-Draft
Intended status: Experimental                          February 17, 2015
Expires: August 21, 2015


                            HTTP/2 Segments
                     draft-kerwin-http2-segments-02

Abstract

   This document introduces the concept of "segments" to HTTP/2, and
   adds a flag to the DATA frame type to allow the expression segments.

   A "segment" is a contiguous block of HTTP message data that can be
   freely split apart and recombined at any time, allowing transmission
   in multiple HTTP/2 frames across network segments with smaller frame
   size limits without risk of permanent fragmentation when traversing
   network segments with much larger limits.

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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   Internet-Drafts are draft documents valid for a maximum of six months
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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 August 21, 2015.

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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   2
   2.  Segments  . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  SETTINGS_USE_SEGMENTS Setting . . . . . . . . . . . . . . . .   3
   4.  SEGMENT and SEGMENT_CONTINUES Flag  . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
     6.1.  HTTP/2 Settings Registry Update . . . . . . . . . . . . .   3
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   This document extends HTTP/2 [I-D.ietf-httpbis-http2] by introducing
   the concept of "segments" to HTTP/2, as a mechanism to combat the
   effects of fragmentation within a stream.  It does this by adding a
   new flag to the DATA frame type ([I-D.ietf-httpbis-http2],
   Section 6.1).

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.  Segments

   A "segment" is a contiguous region of a HTTP/2 message's payload data
   which can be freely fragmented and recombined.  A segment is
   expressed by marking all but the final frame in the segment with the
   SEGMENT_CONTINUES flag (Section 4).  Any data-bearing frame that does
   not have the SEGMENT_CONTINUES flag set, and does not follow one that
   does, comprises a single segment.

   Segments can be used to mitigate the effects of fragmentation within
   a stream.  For example, an endpoint may have a large chunk of data
   which it has to transmit via multiple DATA frames in order to comply
   with frame size limits.  It can mark those frames as a single segment
   so that any downstream peer without the same frame size restrictions
   knows that it can safely coalesce the frames.





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3.  SETTINGS_USE_SEGMENTS Setting

   The following new SETTINGS parameter ([I-D.ietf-httpbis-http2],
   Section 6.5.2) is defined:

   o  "SETTINGS_USE_SEGMENTS" (0xTBA): Informs the remote endpoint of
      whether or not the sender supports the SEGMENT_CONTINUES flag
      (Section 4).  A value of 1 indicates that the sender supports the
      flag.  Any other value MUST be treated as a connection error
      ([I-D.ietf-httpbis-http2], Section 5.4.1) of type PROTOCOL_ERROR.

4.  SEGMENT and SEGMENT_CONTINUES Flag

   The following new flags are defined for the DATA frame
   ([I-D.ietf-httpbis-http2], Section 6.1):

   o  "SEGMENT" (0x10): Bit 5 being set indicates that the current
      segment begins and ends with the current frame.

   o  "SEGMENT_CONTINUES" (0x20): Bit 6 being set indicates that the
      current segment continues after the current frame (see Section 2).
      If the preceding frame did not have the SEGMENT_CONTINUES flag,
      the current segment begins at the start of the current frame.
      Intermediaries MUST NOT coalesce frames across a segment boundary
      and MUST preserve segment boundaries when forwarding frames.

   The SEGMENT and SEGMENT_CONTINUES flag MUST NOT be set on any frames
   unless the remote endpoint has indicated support by sending a
   SETTINGS_USE_SEGMENTS setting (Section 3) with a value of 1.

5.  Security Considerations

   In and of itself, segmentation does not introduce any security
   concerns.  However when used in combination with other features, such
   as compression, known vulnerabilities may be introduced.  See the Use
   of Compression in HTTP/2 ([I-D.ietf-httpbis-http2], Section 10.6).

6.  IANA Considerations

   This document updates the registry for settings in the "Hypertext
   Transfer Protocol (HTTP) 2 Parameters" section.

6.1.  HTTP/2 Settings Registry Update

   This document updates the "HTTP/2 Settings" registry
   ([I-D.ietf-httpbis-http2], Section 11.3).  The entries in the
   following table are registered by this document.




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     +-----------------------+------+---------------+---------------+
     | Name                  | Code | Initial Value | Specification |
     +-----------------------+------+---------------+---------------+
     | SETTINGS_USE_SEGMENTS | TBD  | N/A           | Section 3     |
     +-----------------------+------+---------------+---------------+

7.  Normative References

   [I-D.ietf-httpbis-http2]
              Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer
              Protocol version 2", draft-ietf-httpbis-http2-17 (work in
              progress), February 2015.

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

Author's Address

   Matthew Kerwin

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





























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