HTTP: The Definitive Guide

Appendix C. HTTP Header Reference

It’s almost amusing to remember that the first version of HTTP, 0.9, had no headers. While this certainly had its down sides, its fun to marvel in its simplistic elegance.

Well, back to reality. Today there are a horde of HTTP headers, many part of the specification and still others that are extensions to it. This appendix provides some background on these official and extension headers. It also acts as an index for the various headers in this book, pointing out where their concepts and features are discussed in the running text. Most of these headers are simple up-front; it’s the interactions with each other and other features of HTTP where things get hairy. This appendix provides a bit of background for the headers listed and directs you to the sections of the book where they are discussed at length.

The headers listed in this appendix are drawn from the HTTP specifications, related documents, and our own experience poking around with HTTP messages and the various servers and clients on the Internet.

This list is far from exhaustive. There are many other extension headers floating around on the Web, not to mention those potentially used in private intranets. Nonetheless, we have attempted to make this list as complete as possible. See RFC 2616 for the current version of the HTTP/1.1 specification and a list of official headers and their specification descriptions.