and a server behind it like
``` mkfifo /tmp/myfifo cat /tmp/myfifo | nc -l 12345 > /tmp/myfifo ```
so if you manually type out
CONNECT host:12345 HTTP/1.1
host: host:12345
you can see exactly what's happening. To be fair you can hack curl to support that via curl -x proxy:3333 telnet://host:12345
but that's not exactly what you want and requires curl to have been compiled with telnet support.