After the upstream large refactor, now only WebSocket sockets
have tunneling via HTTP/1 proxies. "Raw" sockets in the normal
socket pool don't have tunneling via HTTP/1 proxies, i.e.
CONNECT headers are not sent, instead the raw payload is sent
as-is to the HTTP/1 proxy, which makes it not work.
For the reference the official code does this:
- HTTP sockets via HTTP/1 proxies: normal pool, no tunneling.
- HTTPS sockets via HTTP/1 proxies: normal pool, no tunneling
but does its own proxy encapsulation.
- WS sockets via HTTP/1 proxies: WS pool, tunneling.
We want the normal pool because the WS pool has some extra
restrictions but we also want tunneling to expose a client socket
with the proxy built in.
Therefore we can force tunneling for all sockets. This will always
send CONNECT headers first and thus break HTTP client sockets via
HTTP/1 proxies, but since we don't use this combination this is ok.
