nghttp2 is an implementation of HTTP/2 and its header compression algorithm
HPACK in C.

The framing layer of HTTP/2 is implemented as a form of reusable C library. On
top of that, we have implemented HTTP/2 client, server and proxy. We have also
developed load test and benchmarking tool for HTTP/2 and SPDY.

WWW: https://nghttp2.org/