Fun fact - I added a pretty feature complete WS connection in Node core (https://github.com/nodejs/node/blob/main/src/inspector_socke...) 7 years ago (it is well-tested - every debug/profiling session goes through it). There's no public API for it because I did not want to deal with politics.

There's rudimentary HTTP server as well (no TLS and such though). All in C++. Should be fairly fast, based on expertise of the Chromium team.