HTTP Proxy 

The following graphic shows how data is transferred with HTTP:

HTTP is a request/response protocol. Only the browser can send requests, and only the server can respond with a suitable response. This is also known as the HTTP request/response cycle. Many HTTP requests may still be open in the browser and waiting for a response from the server. Each HTTP response is always correctly mapped to the HTTP request that started this cycle.

The server is frequently outside a firewall, however, so that it is not possible to communicate directly with that server. This is why companies place HTTP proxy servers on the firewall, where one part is within the firewall, and the other part is outside it. The browser is configured so that it uses the proxy server as a representative for handling HTTP requests. This means that instead of calling the server for every request, the browser contacts the proxy server with the HTTP request and waits until the proxy server returns the HTTP response.

From this you can see that the browser is familiar with the concept of a mediating agent, which can be configured in such a way to handle all HTTP requests on its behalf. The browser contacts the proxy server and that’s it for the browser.

The browser now has to be configured so that it uses a different proxy, the proxy for HTTP tracing

The browser will now pass the HTTP request to the proxy server as usual. The proxy logs the data traffic and passes the request directly to the proxy server that performs the actual work. On the way back, the data traffic is held again in a trace.