i have a basic understanding of how HTTP works and is similar to what is described here But my problem is when using glype based proxies for example(i have no experience with others) and you carry out these steps:
The request looks like
Get http://www.google.com /HTTP 1.0
host: www.google.com
So how does apache know what php script it should foward this request to?
Assuming glype is just a regular proxy server it's quite simple. After configuring your browser to use a proxy (by providing it's IP address), each request made by your browser first checks with the proxy server to see if it has a cached copy of the requested URL (which in this case is http://www.google.com index page). If it does, the proxy returns it, otherwise the browser requests the document from the real server (google.com, in your example) and saves a copy on the proxy server so the next request doesn't have to get it from the real server.
The idea is that when lots of users are repeatedly requesting the same document from a remote source, a proxy server, typically for a local network will be able to serve the content (the document and images and other stuff) more quickly. That was probably true ten or twenty years ago when large companies had many users and limited bandwidth. Today, proxy servers are of little value in normal web browsing -- most web pages (like the Google home page) are dynamic, and send headers that instruct proxies to not cache the content. Further, browsers cache stuff now, and in most cases, bandwidth is available. To be sure, this is not true everywhere in the world and for all web pages, but mostly proxy servers whose purpose is to cache data are a vestige of the past.
