15.9 Location Headers and Spoofing .....................144
   16 Acknowledgments.......................................144
   17 References............................................146
   18 Authors' Addresses....................................149
   19 Appendices............................................150
    19.1 Internet Media Type message/http ..................150
    19.2 Internet Media Type multipart/byteranges ..........150
    19.3 Tolerant Applications .............................151
    19.4 Differences Between HTTP Entities and
    MIME Entities...........................................152
     19.4.1 Conversion to Canonical Form ...................152
     19.4.2 Conversion of Date Formats .....................153
     19.4.3 Introduction of Content-Encoding ...............153
     19.4.4 No Content-Transfer-Encoding ...................153
     19.4.5 HTTP Header Fields in Multipart Body-Parts .....153
     19.4.6 Introduction of Transfer-Encoding ..............154
     19.4.7 MIME-Version ...................................154
    19.5 Changes from HTTP/1.0 .............................154
     19.5.1 Changes to Simplify Multi-homed Web Servers and
     Conserve IP Addresses .................................155
    19.6 Additional Features ...............................156
     19.6.1 Additional Request Methods .....................156
     19.6.2 Additional Header Field Definitions ............156
    19.7 Compatibility with Previous Versions ..............160
     19.7.1 Compatibility with HTTP/1.0 Persistent
     Connections............................................161












 
RFC 2068                        HTTP/1.1                    January 1997


1 Introduction

1.1 Purpose

   The Hypertext Transfer Protocol (HTTP) is an application-level
   protocol for distributed, collaborative, hypermedia information
   systems. HTTP has been in use by the World-Wide Web global
   information initiative since 1990. The first version of HTTP,
   referred to as HTTP/0.9, was a simple protocol for raw data transfer
   across the Internet. HTTP/1.0, as defined by RFC 1945 [6], improved
   the protocol by allowing messages to be in the format of MIME-like
   messages, containing metainformation about the data transferred and
   modifiers on the request/response semantics. However, HTTP/1.0 does
   not sufficiently take into consideration the effects of hierarchical
   proxies, caching, the need for persistent connections, and virtual
   hosts. In addition, the proliferation of incompletely-implemented
   applications calling themselves "HTTP/1.0" has necessitated a
   protocol version change in order for two communicating applications
   to determine each other's true capabilities.

   This specification defines the protocol referred to as "HTTP/1.1".
   This protocol includes more stringent requirements than HTTP/1.0 in
   order to ensure reliable implementation of its features.

   Practical information systems require more functionality than simple
   retrieval, including search, front-end update, and annotation. HTTP
   allows an open-ended set of methods that indicate the purpose of a
   request. It builds on the discipline of reference provided by the
   Uniform Resource Identifier (URI) [3][20], as a location (URL) [4] or
   name (URN) , for indicating the resource to which a method is to be
   applied. Messages are passed in a format similar to that used by
   Internet mail as defined by the Multipurpose Internet Mail Extensions
   (MIME).

   HTTP is also used as a generic protocol for communication between
   user agents and proxies/gateways to other Internet systems, including
   those supported by the SMTP [16], NNTP [13], FTP [18], Gopher [2],
   and WAIS [10] protocols. In this way, HTTP allows basic hypermedia
   access to resources available from diverse applications.

1.2 Requirements

   This specification uses the same words as RFC 1123 [8] for defining
   the significance of each particular requirement. These words are:

   MUST
      This word or the adjective "required" means that the item is an
      absolute requirement of the specification.




 
RFC 2068                        HTTP/1.1                    January 1997


   SHOULD
      This word or the adjective "recommended" means that there may