That'd be RFC (checks notes) 1945 for HTTP1.0 and later RFC (checks notes again) 2616 for HTTP 1.1. I think there's HTTP 0.9 but I went directly for 1.0
Fwiw it's entirely possible to build a web server by listening on port 80 and reading the text stream and writing to the output stream, no libraries no frameworks no apache no ngninx. And I don't mean you need to rebuild a general purpose an apache like server, maybe for a landing page you can just serve a static page and you will be implementing a very small subset of HTTP.
That'd be RFC (checks notes) 1945 for HTTP1.0 and later RFC (checks notes again) 2616 for HTTP 1.1. I think there's HTTP 0.9 but I went directly for 1.0
Fwiw it's entirely possible to build a web server by listening on port 80 and reading the text stream and writing to the output stream, no libraries no frameworks no apache no ngninx. And I don't mean you need to rebuild a general purpose an apache like server, maybe for a landing page you can just serve a static page and you will be implementing a very small subset of HTTP.