How does a HTTP Proxy utilize the HTTP protocol? a Proxy RFC?

http, http-proxy, proxy

Solution

The requirements on HTTP Proxy servers are specified within

- RFC7230 - Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing

- RFC7231 - Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content

Problem

How does one go about implementing a HTTP proxy compared to implementing a HTTP webserver, what are the differences? Is there a definitive guide or RFC or a helpful book on this subject?

Original source