HTTP: The Definitive Guide

HTTP Connection Handling

The first two sections of this chapter provided a fire-hose tour of TCP connections and their performance implications. If you’d like to learn more about TCP networking, check out the resources listed at the end of the chapter.

We’re going to switch gears now and get squarely back to HTTP. The rest of this chapter explains the HTTP technology for manipulating and optimizing connections. We’ll start with the HTTP Connection header, an often misunderstood but important part of HTTP connection management. Then we’ll talk about HTTP’s connection optimization techniques.

The Oft-Misunderstood Connection Header

HTTP allows a chain of HTTP intermediaries between the client and the ultimate origin server (proxies, caches, etc.). HTTP messages are forwarded hop by hop from the client, through intermediary devices, to the origin server (or the reverse).

In some cases, two adjacent HTTP applications may want to apply a set of options to their shared connection. The HTTP Connection header field has a comma-separated list of connection tokens that specify options for the connection that aren’t propagated to other connections. For example, a connection that must be closed after sending the next message can be indicated by Connection: close.

The Connection header sometimes is confusing, because it can carry three different types of tokens:

• HTTP header field names, listing headers relevant for only this connection

• Arbitrary token values, describing nonstandard options for ...