fix: ALPN missed when using socks5 proxy with rustls backend

[cxw620]

reopen PR, fix #2118

[cxw620]

I've tested this PR and it's working well. Would you mind taking a look at it? Thanks!

[cxw620]

@seanmonstar Could you provide an update on this PR? Any feedback or comments on it? Thanks :D

[seanmonstar]

Shouldn't this still use the proxy TLS? Should the fix instead be that we set ALPN on the proxy TLS?

[cxw620]

we can see when connect_via_proxy and ProxyScheme::Socks5, we call self.connect_socks(dst, proxy_scheme).await, dst is our target.

            #[cfg(feature = "__rustls")]
            Inner::RustlsTls { tls, .. } => {
                if dst.scheme() == Some(&Scheme::HTTPS) {
                    use std::convert::TryFrom;
                    use tokio_rustls::TlsConnector as RustlsConnector;

                    let tls = tls.clone();
                    let host = dst.host().ok_or("no host in url")?.to_string();
                    let conn = socks::connect(proxy, dst, dns).await?; // create proxy tunnel through socks server and connect to dst.
                    let conn = TokioIo::new(conn);
                    let conn = TokioIo::new(conn);
                    let server_name =
                        rustls_pki_types::ServerName::try_from(host.as_str().to_owned())
                            .map_err(|_| "Invalid Server Name")?;
                    let io = RustlsConnector::from(tls) // here we create TLS connector for HTTPS through socks tunnel, so `tls` should not be proxy TLS.
                        .connect(server_name, conn)
                        .await?;
                    let io = TokioIo::new(io);
                    return Ok(Conn {
                        inner: self.verbose.wrap(RustlsTlsConn { inner: io }),
                        is_proxy: false,
                        tls_info: false,
                    });
                }
            }