feature request: http/3 client

[liudongmiao]

feature request: http/3 client

[liudongmiao]

LiteSpeed QUIC is a quic library, and use libevent in examples.

[liudongmiao]

@azat IMO, libevent don't have to offer something like bufferevent_sock_udp, or even make bufferevent_openssl support quic. However, libevent should return the size of bufferevent_private, so that bufferevent can be extend like bufferevent_openssl (or buffereent_ssl in master), bufferevent_filter, bufferevent_pair, etc.

If we have no bufferevent_private, then most functions of bufferevent_xxx cannot be used, as most of them requires the bufferevent is bufferevent_private (the lock).

In the way of implementing openssl quic / http3, I use the bufferevent_socket (core part of bufferevent_private), then rewrite the callback of ev_write and ev_read, and store the extend part like bufferevent_filter / bufferevent_openssl as bufferevent_context in watermark read / write low, as I found they are only be called in ev_write / ev_read callback, and as I rewrite the callback, so I can use it. (size_t have the same size of void *).

BTW, I use the same trick to implement socket udp (udp socket have special recv and send, and for server, we use the same sock to recv), and implement a simple http2, and websocket over http2, of course, and websocket over http3.