RFC 3229 (rfc3229) - Page 2 of 49

Delta encoding in HTTP

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............................ 40
             10.8.1 Retain directive................................. 40
             10.8.2 IM directive..................................... 40
        10.9 Use of compression with delta encoding.................. 41
        10.10 Delta encoding and multipart/byteranges................ 42
   11 Quantifying the protocol overhead.............................. 42
   12 Security Considerations........................................ 44
   13 Acknowledgements............................................... 44
   14 Intellectual Property Rights................................... 44



Mogul, et al.               Standards Track