1. Basic TCP sockets layer: Listen on ports, accept client connections & send/receive data
2. Implement a buffered reader so that you can read requests one line (delimited by CRLF) at a time.
3. Read the very first line. Parse out the method, the request version and the path.
4. Implement header parsing for the "Header: value" syntax. Don't forget unfolding folded headers.
5. Check the request method, content type and content size to determine how/if the body will be read.
6. Implement decoding of content based on content type.
7. If you're going to support HTTP 1.1, implement things like "100 Continue", keep-alive, chunked transfer.
8. Add robustness/security measures like detecting incomplete requests, limiting max number of clients etc.
9. Shrink wrap your code and open-source it :)

Source: https://stackoverflow.com/questions/176409/build-a-simple-http-server-in-c

• HTTP Made Really Easy
• tinyhttpd - a very simple webserver for educational uses