The project #micro HTTP server in C is designed to implement this protocol. This is where you'll find the low-level details discussions.
This project documents the protocol itself, its definitions and evolutions, to help other clients and servers interoperate.
HTTaP could be described as an attempt to formalise requests and replies between a HTTP-capable client and a HTTaP server, as well as all the surrounding parameters.
Think of HTTaP as a WebAPI for hardware and logic circuits.
For example it can embed/encapsulate SCPI commands over Ethernet or Wifi instead of RS232 or USB. No need to install stupid Windows drivers or lousy (binary, non-free and obfuscated) applications !
HTTaP messages are very simple : just GET or PUT values to certain places, using JSON notation. This is intentionally simple but limited so actual work is achieved through convoluted sequences of small atomic messages.
Standard addresses provide well-known points that provide enough informations to discover/explore the system, its hierarchy and capabilities, through individual client requests.
This is why the server needs to exchange many small packets "in order", in lock-step sequences, and fast, so the HTTaP server disables TCP's Nagle congestion-avoidance algorithm (this saves about 400ms second per round-trip).
The user is normally directly connected to the server so the latency is usually low and HTTaP doesn't implement elaborate bandwidth-enhancement algorithms. Real-time latency matters more because it is usually connected to a GUI.