HTTP: The Definitive Guide

Architectural Components of the Web

In this overview chapter, we’ve focused on how two web applications (web browsers and web servers) send messages back and forth to implement basic transactions. There are many other web applications that you interact with on the Internet. In this section, we’ll outline several other important applications, including:

Proxies

HTTP intermediaries that sit between clients and servers

Caches

HTTP storehouses that keep copies of popular web pages close to clients

Gateways

Special web servers that connect to other applications

Tunnels

Special proxies that blindly forward HTTP communications

Agents

Semi-intelligent web clients that make automated HTTP requests

Proxies

Let’s start by looking at HTTP proxy servers , important building blocks for web security, application integration, and performance optimization.

As shown in Figure 1-11, a proxy sits between a client and a server, receiving all of the client’s HTTP requests and relaying the requests to the server (perhaps after modifying the requests). These applications act as a proxy for the user, accessing the server on the user’s behalf.

Figure 1-11. Proxies relay traffic between client and server

Proxies are often used for security, acting as trusted intermediaries through which all web traffic flows. Proxies can also filter requests and responses; for example, to detect application viruses in corporate downloads ...