Delta encoding in HTTP
RFC 3229
Document | Type |
RFC - Proposed Standard
(January 2002; No errata)
Was draft-mogul-http-delta (app)
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Authors | Arthur van Hoff , Fred Douglis , Balachander Krishnamurthy , Yaron Goland , Daniel Hellerstein , Anja Feldmann , Jeffrey Mogul | ||
Last updated | 2013-03-02 | ||
Stream | Legacy | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | Legacy state | (None) | |
Consensus Boilerplate | Unknown | ||
RFC Editor Note | (None) | ||
This information refers to IESG processing after the RFC was initially published: | |||
IESG | IESG state | RFC 3229 (Proposed Standard) | |
Telechat date | |||
Responsible AD | Ned Freed | ||
IESG note | published January 2002 | ||
Send notices to | (None) |
Network Working Group J. Mogul Request for Comments: 3229 Compaq WRL Category: Standards Track B. Krishnamurthy F. Douglis AT&T A. Feldmann Univ. of Saarbruecken Y. Goland A. van Hoff Marimba D. Hellerstein ERS/USDA January 2002 Delta encoding in HTTP Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document describes how delta encoding can be supported as a compatible extension to HTTP/1.1. Many HTTP (Hypertext Transport Protocol) requests cause the retrieval of slightly modified instances of resources for which the client already has a cache entry. Research has shown that such modifying updates are frequent, and that the modifications are typically much smaller than the actual entity. In such cases, HTTP would make more efficient use of network bandwidth if it could transfer a minimal description of the changes, rather than the entire new instance of the resource. This is called "delta encoding." Mogul, et al. Standards Track [Page 1] RFC 3229 Delta encoding in HTTP January 2002 Table of Contents 1 Introduction.................................................... 3 1.1 Related research and proposals........................... 4 2 Goals........................................................... 5 3 Terminology..................................................... 6 4 The HTTP message-generation sequence............................ 8 4.1 Relationship between deltas and ranges................... 11 5 Basic mechanisms................................................ 13 5.1 Background: an overview of HTTP cache validation......... 13 5.2 Requesting the transmission of deltas.................... 14 5.3 Choice of delta algorithm and format..................... 16 5.4 Identification of delta-encoded responses................ 16 5.5 Guaranteeing cache safety................................ 17 5.6 Transmission of delta-encoded responses.................. 18 5.7 Examples of requests combining Range and delta encoding.. 19 6 Encoding algorithms and formats................................. 22 7 Management of base instances.................................... 23 7.1 Multiple entity tags in the If-None-Match header......... 24 7.2 Hints for managing the client cache...................... 25 8 Deltas and intermediate caches.................................. 27 9 Digests for data integrity...................................... 28 10 Specification.................................................. 28 10.1 Protocol parameter specifications....................... 28 10.2 IANA Considerations..................................... 30 10.3 Basic requirements for delta-encoded responses.......... 30 10.4 Status code specifications.............................. 30 10.4.1 226 IM Used...................................... 31 10.5 Header specifications................................... 31 10.5.1 Delta-Base....................................... 31 10.5.2 IM............................................... 32 10.5.3 A-IM............................................. 33 10.6 Caching rules for 226 responses......................... 35 10.7 Rules for deltas in the presence of content-codings..... 36 10.7.1 Rules for generating deltas in the presence of content-codings.................................. 37 10.7.2 Rules for applying deltas in the presence of content-codings.................................. 37 10.7.3 Examples for using A-IM, IM, and content-codings. 38 10.8 New Cache-Control directives............................ 40Show full document text