The “core” semantics of the HTTP protocol are defined by:
Those semantics are expressed “on the wire” in three ways:
Later versions of HTTP offer field compression:
These RFCs collectively obsolete all preceding RFCs defining HTTP, includingRFC 1945,RFC 2068,RFC 2616,RFC 2617,RFC 7230-5, andRFC 7540.
Also relevant is the Structured Field Values specification, which is used in a growing number of headers and trailers:
Protocols built “on top” of HTTP should follow Best Current Practice, as documented here:
There are a large number of HTTP extensions, including methods, status codes and headers. It’s important to note that they are all “part of” HTTP, as long as they’re listed in the appropriate registries:
Individual headers have their own registries that regulate permissible values, including:
This is apartial list of HTTP-relevant specifications, here for convenience. For the completelist of HTTP extensions, see the relevant registry.