h11

h11 is a pure-Python, bring-your-own-I/O implementation of HTTP/1.1, heavily inspired by hyper-h2. It contains no networking code whatsoever — you supply the bytes in and out — making it usable with any I/O model: synchronous, threaded, asyncio, trio, or custom. It models the HTTP exchange as a strict state machine emitting typed event objects (Request, Response, Data, EndOfMessage, etc.) and enforces spec conformance on both incoming and outgoing messages. Current version is 0.16.0, released in 2025 as a security fix; releases are infrequent and focused on correctness. It has no dependencies outside the Python standard library.