WIP: SNI-aware proxy with tokio

[selfhoster1312]

This is really bad code and does everything very wrong, sorry about that, it's just a proof-of-concept. I just submitted this because it took me a while to figure it out already, and people seemed interested in #58 (5 upvotes at the time of writing).

Supports:

• tokio runtime
• monoio runtime
• TCP connections
• QUIC connections

It's very quick & dirty, as it will peek in the stream to find the TLS handshake (i couldn't find a peek equivalent in monoio, so only tokio is supported for now), which will be parsed a second time if the connection is not reverse proxied without TLS termination.

Also, i mostly have no idea what i'm doing with that backend TcpStream reading/writing, i just hacked this around, but i'm guessing it's possible to pipe actual tcp_stream into dest_stream without dark magic (i just don't know how).

Testing

It's using the proxy_tls directive in vhosts. For example:

google.com:4443 {
  proxy_tls "142.250.178.131:443"
}

Now you can curl it:

curl -v -4 --connect-to 'google.com:443:127.0.0.1:4443' https://google.com

Additional notes

• it's very cumbersome to get SNI from rustls without consuming the connection (hence the peeked buffer hack), there's plenty of issues about it upstream, and i don't understand why the maintainers don't want to make it easier (i had to fork rustls to make more types public, but there may be a simpler way)