HTTP traffic is split between the webserver and a transparent HTTP proxy on the customer site and the HTTP proxy server and the end-hosts.
The transparent HTTP proxy fakes the end-points; to the HTTP web server it pretends to be the customer accessing it and to the customer the HTTP proxy appears to be the web server (faked IP addresses). Accordingly there are 2 TCP connections to be considered here.
The proxy receives a HTTP request from the customer to the webserver. It then forwards this request to the webserver and WAITS until it has received the whole reply (this is essential, as it needs to analyze the whole reply to decide if it is bad or not). If the content of that HTTP reply is dynamic, the length is not known. With HTTP1.1 a TCP session is not built for every object but remains intact untill a timeout has occured.This means the proxy has to wait until the TCP session gets torn down, to be sure there is not more content coming. When it has received the whole reply it will forward that reply to the customer who asked for it. Of course the customer will suffer from a major delay.
– Main.ChrisWelti - 03 Mar 2005