Web Caching and Replication

5.9. Learning the Proxy Chain

A client may want to know the chain of proxies its requests take on their way to origin servers. As we show in Chapter 8, a proxy in some cases affects (or even disrupts) the service clients receive from certain Web sites; it is therefore important that a client be aware of the existence of the proxy so that the client can use appropriate request headers to go directly to the origin servers in such situations.

HTTP 1.1 provides a via header and a TRACE request method, which together allow the client to know if a proxy exists. The via header keeps track of proxies and protocol versions involved in transferring the request from the client to the server. Every proxy that processes the request must append an entry to ...