HttpServer fails to work with Unix sockets

[robert-ancell]

Creating an HttpServer with a Unix socket fails to accept connection, due to attempting to set the TCP_NO_DELAY socket option on the sockets, which is not supported for this socket type.

e.g.

var server = await HttpServer.bind(InternetAddress('/tmp/test-socket', type: InternetAddressType.unix), 0);
server.listen((request) {
  print(request.method);
});

Connecting using an HTTP client...

curl --unix-socket /tmp/test-socket http://localhost/

...causes the server to hit an exception:

Unhandled exception:
OS Error: Operation not supported, errno = 95

Note that this exception only occurs with a fix to Socket.setOption, since it currently hits an assertion with Unix sockets.

[a-siva]

Please see https://dart-review.googlesource.com/c/sdk/+/199640 for a potential fix to the problem along with the test case you mention above.