http/3 demo: Find a suitable library

[arapov]

No description provided.

[paulidale]

Curl is looking good: https://github.com/curl/curl

[t8m]

I was looking for curiosity at curl and it seems that it does not have its own http3 library. Instead it uses one of MSQUIC, nghttp3+ngtcp2 or quiche. I was afraid this basically makes it unusable for our purposes.

However then I was looking at how curl uses nghttp3+ngtcp2 and realized that these aren't tightly coupled so it should be quite easily possible to replace ngtcp2 calls in curl with calls to libssl.

[paulidale]

It looked like it was building the HTTP requests itself and relying on one of those three for the QUIC side of things but I needed to dig further.

[paulidale]

Replacing ngtcp2 and using curl + nghttp3 looks like it might be workable. It will be a reasonable effort -- there are quite a few callbacks and direct calls to support and not all appear to be quite the way we're doing things:

• multi-steam is required (it opens 3 uni directional streams)
• there will have to be some quictls aware code removed/replaced in Curl, none in nghttp3

nghttp3 appears to be very clean having no direct calls to ngtcp2.

[paulidale]

This assessment should still be considered somewhat rudimentary.