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Versions: 00 01 02 03 04 05 06 draft-ietf-hybi-websocket-perframe-compression

HyBi Working Group                                            T. Yoshino
Internet-Draft                                              Google, Inc.
Intended status: Standards Track                          April 27, 2011
Expires: October 29, 2011


                 WebSocket Per-frame DEFLATE Extension
           draft-tyoshino-hybi-websocket-perframe-deflate-00

Abstract

   This specification defines a per-frame DEFLATE compression extension
   for the WebSocket protocol.  This extension enables compressing only
   the Application Data part of WebSocket frames using DEFLATE
   compression while leaving the other parts such as opcode, payload
   length, the Extension Data part untouched.

Status of this Memo

   This Internet-Draft is submitted to IETF 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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   This Internet-Draft will expire on October 29, 2011.

Copyright Notice

   Copyright (c) 2011 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



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   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Background . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Extension Overview . . . . . . . . . . . . . . . . . . . .  3
   2.  Conformance Requirements . . . . . . . . . . . . . . . . . . .  4
   3.  Extension Negotiation  . . . . . . . . . . . . . . . . . . . .  5
   4.  Detailed Specification . . . . . . . . . . . . . . . . . . . .  6
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
     6.1.  Registration of the "deflate-application-data"
           WebSocket Extension Keyword  . . . . . . . . . . . . . . .  8
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11


























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1.  Introduction

1.1.  Background

   _This section is non-normative._

   The WebSocket protocol is designed to allow for extensions
   [I-D.ietf-hybi-thewebsocketprotocol].  This enables use of
   compression extension to reduce the amount of data to be sent over
   network.

   The WebSocket protocol specification contains built-in compression
   extension "deflate-stream" that applies DEFLATE to everything
   including header octets such as opcode and payload length.  It's
   simple, however it requires intermediaries that are not interested in
   the contents of the Application Data part to decompress received
   octets using DEFLATE to see opcode, etc.

1.2.  Extension Overview

   _This section is non-normative._

   Per-frame DEFLATE extension adds another DEFLATE [RFC1951] based
   compression option to the WebSocket protocol.  Per-frame DEFLATE
   extension compresses only the octets in the Application Data part of
   a frame.  Header octets are unchanged by this extension.

   To align the end of compressed data to octet boundary, this extension
   uses the algorithm described in the Section 2.1 of the PPP Deflate
   Protocol [RFC1979].  The frame sender keeps using the same LZ77
   sliding window across multiple frames [LZ77].

   This extension doesn't use any of reserved bits, opcodes or Extension
   Data part.

   The simplest "Sec-WebSocket-Extensions" header in the opening
   handshake from the client that negotiates only per-frame DEFLATE
   extension is the following:

        Sec-WebSocket-Extensions: deflate-application-data

   The server also sends the same header to accept the use of this
   compression extension.








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2.  Conformance Requirements

   Everything in this specification except for sections explicitly
   marked non-normative is normative.

   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].











































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3.  Extension Negotiation

   The registered extension token for this extension is
   "deflate-application-data".

   To use per-frame DEFLATE extension, a user-agent MUST send an opening
   handshake request with the "deflate-application-data" extension token
   included in its "Sec-WebSocket-Extensions" header.

   To accept use of per-frame DEFLATE extension requested by the user-
   agent, a server MUST send an opening handshake response with the
   "deflate-application-data" extension token included in its
   "Sec-WebSocket-Extensions" header.

   Any extension parameter MUST NOT be attached to
   "deflate-application-data" extension token.

   Once per-frame DEFLATE extension is accepted, both endpoints MUST use
   the algorithm described in Section 4 in sending frames.
































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4.  Detailed Specification

   This extension does not use any of reserved bits, opcodes or the
   Extension Data part in a WebSocket frame.

   This extension operates only on Data Frames, and only on the
   Application Data therein (it does not affect the Extension Data
   portion of the Payload Data).

   A sender using this extension MUST compress all octets of the
   Application Data part using DEFLATE [RFC1951].  The sender MAY use
   multiple blocks to compress data for one frame.  The sender MAY use
   blocks with any effective "BTYPE" defined in [RFC1951] for one frame.
   "BFINAL" bit MUST NOT be set for any block.  The sender MUST use the
   algorithm described in the Data paragraph of the Section 2.1 of the
   PPP Deflate Protocol [RFC1979] to align the end of the compressed
   data to octet boundary.  That is that the sender MUST append an empty
   uncompressed block to the tail of the compressed data, and then
   remove 4 octets from the tail of the concatenated data.  The sender
   MUST put this data (the octets left after removing 4 octets) in the
   Application Data part instead of the original data.  The payload
   length field of the frame MUST be the number of octets in the
   Extension Data part and the Application Data part after this process.
   The senders MAY keep using the same LZ77 sliding window across
   multiple frames [LZ77].

   A receiver MUST append 4 octets of 0x00 0x00 0xff 0xff to the tail of
   the received octets in the Application Data part and decompress the
   concatenated octets using DEFLATE to get the original octets for the
   Application Data part.  The receiver MUST keep using the same LZ77
   sliding window for all frames on the same WebSocket connection.  The
   receiver MUST use 32768 byte LZ77 sliding window.



















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5.  Security Considerations

   There's no security concern for now.
















































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6.  IANA Considerations

6.1.  Registration of the "deflate-application-data" WebSocket Extension
      Keyword

   Name of token.
      deflate-application-data

   Author/Change controller
      IETF <iesg@ietf.org>

   Contact
      HYBi <hybi@ietf.org>

   References
      RFC XXX

   The "deflate-application-data" token is used in the
   "Sec-WebSocket-Extensions" header in the WebSocket opening handshake
   to negotiate use of per-frame DEFLATE compression extension.































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7.  Acknowledgements

   Special thanks to Patrick McManus who wrote up the initial version of
   DEFLATE-based compression extension specification for the WebSocket
   protocol which I referred when I write this specification.














































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8.  References

8.1.  Normative References

   [I-D.ietf-hybi-thewebsocketprotocol]
              Fette, I., "The WebSocket protocol",
              draft-ietf-hybi-thewebsocketprotocol (work in progress),
              April 2011.

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

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

   [LZ77]     Ziv, J. and A. Lempel, "A Universal Algorithm for
              Sequential Data Compression", IEEE Transactions on
              Information Theory, Vol. 23, No. 3, pp. 337-343.

8.2.  Informative References

   [RFC1979]  Woods, J., "PPP Deflate Protocol", RFC 1979, August 1996.





























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Author's Address

   Takeshi Yoshino
   Google, Inc.

   Email: tyoshino@google.com













































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