Specification

http://www.w3.org/Protocols/rfc2616/rfc2616.html

http://www.w3.org/Protocols/HTTP/1.1/rfc2616.pdf

Guide

http://www.jmarshall.com/easy/http/

Code/libs

http://msdn.microsoft.com/en-us/library/windows/desktop/aa364510(v=vs.85).aspx

https://code.google.com/p/mongoose/

http://pocoproject.org/

http://think-async.com/Asio

http://cpp-netlib.org/

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3388.pdf

WebSockets

Browser

http://dev.w3.org/html5/websockets/

pdf rfc6455

http://tools.ietf.org/pdf/rfc6455.pdf

online

http://tools.ietf.org/html/rfc6455