HTTP: The Definitive Guide

Web Intermediaries

Web proxy servers are middlemen that fulfill transactions on the client’s behalf.Without a web proxy, HTTP clients talk directly to HTTP servers. With a web proxy, the client instead talks to the proxy, which itself communicates with the server on the client’s behalf. The client still completes the transaction, but through the good services of the proxy server.

HTTP proxy servers are both web servers and web clients. Because HTTP clients send request messages to proxies, the proxy server must properly handle the requests and the connections and return responses, just like a web server. At the same time, the proxy itself sends requests to servers, so it must also behave like a correct HTTP client, sending requests and receiving responses (see Figure 6-1). If you are creating your own HTTP proxy, you’ll need to carefully follow the rules for both HTTP clients and HTTP servers.

Figure 6-1. A proxy must be both a server and a client

Private and Shared Proxies

A proxy server can be dedicated to a single client or shared among many clients. Proxies dedicated to a single client are called private proxies. Proxies shared among numerous clients are called public proxies.

Public proxies

Most proxies are public, shared proxies. It’s more cost effective and easier to administer a centralized proxy. And some proxy applications, such as caching proxy servers, become more useful ...