Compression Extensions for WebSocket
RFC 7692

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Internet Engineering Task Force (IETF)                        T. Yoshino
Request for Comments: 7692                                  Google, Inc.
Category: Standards Track                                  December 2015
ISSN: 2070-1721

                  Compression Extensions for WebSocket

Abstract

   This document defines a framework for creating WebSocket extensions
   that add compression functionality to the WebSocket Protocol.  An
   extension based on this framework compresses the payload data portion
   of WebSocket data messages on a per-message basis using parameters
   negotiated during the opening handshake.  This framework provides a
   general method for applying a compression algorithm to the contents
   of WebSocket messages.  Each compression algorithm has to be defined
   in a document defining the extension by specifying the parameter
   negotiation and the payload transformation algorithm in detail.  This
   document also specifies one specific compression extension using the
   DEFLATE algorithm.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc7692.

Yoshino                      Standards Track                    [Page 1]
RFC 7692          Compression Extensions for WebSocket     December 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
   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. Conformance Requirements and Terminology ........................3
   3. Complementary Terminology .......................................4
   4. WebSocket Per-Message Compression Extension .....................5
   5. Extension Negotiation ...........................................5
      5.1. General Negotiation Flow ...................................9
      5.2. Negotiation Examples .......................................9
   6. Framing ........................................................10
      6.1. Compression ...............................................10
      6.2. Decompression .............................................12
   7. The "permessage-deflate" Extension .............................12
      7.1. Extension Parameters ......................................14
           7.1.1. Context Takeover Control ...........................14
           7.1.2. Limiting the LZ77 Sliding Window Size ..............16
           7.1.3. Examples ...........................................18
      7.2. Message Payload Transformation ............................19
           7.2.1. Compression ........................................19
           7.2.2. Decompression ......................................21
           7.2.3. Examples ...........................................22
      7.3. Implementation Notes ......................................25
   8. Security Considerations ........................................25
   9. IANA Considerations ............................................26
      9.1. Registration of the "permessage-deflate" WebSocket
           Extension Name ............................................26
      9.2. Registration of the "Per-Message Compressed"
           WebSocket Framing Header Bit ..............................26
   10. References ....................................................27
      10.1. Normative References .....................................27
      10.2. Informative References ...................................27
   Acknowledgements ..................................................28
   Author's Address ..................................................28

Yoshino                      Standards Track                    [Page 2]
RFC 7692          Compression Extensions for WebSocket     December 2015

1.  Introduction

   This document specifies a framework for adding compression
   functionality to the WebSocket Protocol [RFC6455].  The framework