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Tuesday, October 30, 2007

The Hypertext Transfer Protocol (HTTP) Entity Tag ("ETag") Response

A revised version of the IETF specification "The Hypertext Transfer
Protocol (HTTP) Entity Tag ('ETag') Response Header in Write Operations"
has been released in connection with the formation of a new HTTPbis
Working Group activity. The Hypertext Transfer Protocol (HTTP)
specifies a state identifier, called "Entity Tag", to be returned in
the "ETag" response header. However, the description of this header
for write operations such as PUT is incomplete, and has caused confusion
among developers and protocol designers, and potentially interoperability
problems. This document explains the problem in detail and suggests
both a clarification for a revision to the HTTP/1.1 specification
(RFC 2616) and a new header for use in responses, making HTTP entity
tags more useful for user agents that want to avoid round-trips to the
server after modifying a resource. The RFC 2616 specification is a bit
vague about what an ETag response header upon a write operation means,
but this problem is somewhat mitigated by the precise definition of a
response header. The proposal for enhancing RFC 2616 in this regard is
made in document Section 3. More Information See also the related issue 'Clarify "Requested Variant"': Click Here

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