Would redbean work for your purpose? It's very lightweight and fun to work with, though not suited for everything.
I'm looking for something more like websocketpp[0], or even just grpc without a requisite proxy. uWebsockets looks really promising, being header only, but in the fine print requires a runtime library. unfortunately, none of that ecosystem seems to use cmake, making integrating it that much more of a pain.
why use cpp for this, I'm sure some HNer will ask. the ray tracer itself is using cuda, that's why. I've also debated
- running it as a grpc server and having some proxy in a more web-accessible language
- creating python bindings and using python to make a websocket/http server for it
neither of those are out of the question, but they're not my first choices, because I'd like to keep the build & execution simple. introducing dependencies, especially other executables, is in conflict with that.
i don't need anything particularly scalable -- a threaded implementation, or one using select() would be fine, if not preferable.