Gracefully handle trying to connect to a UNIX socket on Windows

[michaeloliverx]

Running this code on a Windows machine:

import httpcore

http = httpcore.ConnectionPool(uds="/var/run/docker.sock")
response = http.request("GET", "http://docker/info")

Results in the following:

Traceback (most recent call last):
  File <omitted>\fix-unix-socket.py", line 4, in <module>
    response = http.request("GET", "http://docker/info")
  File <omitted>\httpcore\_sync\interfaces.py", line 43, in request
    response = self.handle_request(request)
  File <omitted>\httpcore\_sync\connection_pool.py", line 252, in handle_request
    raise exc
  File <omitted>\httpcore\_sync\connection_pool.py", line 236, in handle_request
    response = connection.handle_request(request)
  File <omitted>\httpcore\_sync\connection.py", line 86, in handle_request      
    raise exc
  File <omitted>\httpcore\_sync\connection.py", line 63, in handle_request      
    stream = self._connect(request)
  File <omitted>\httpcore\_sync\connection.py", line 121, in _connect
    stream = self._network_backend.connect_unix_socket(
  File <omitted>\httpcore\backends\sync.py", line 106, in connect_unix_socket   
    sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
AttributeError: module 'socket' has no attribute 'AF_UNIX'

Do we want to handle it here?

httpcore/httpcore/backends/sync.py

Lines 98 to 109 in faa166c

	def connect_unix_socket(
	self, path: str, timeout: typing.Optional[float] = None
	) -> NetworkStream: # pragma: nocover
	exc_map: ExceptionMapping = {
	socket.timeout: ConnectTimeout,
	OSError: ConnectError,
	}
	with map_exceptions(exc_map):
	sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
	sock.settimeout(timeout)
	sock.connect(path)
	return SyncStream(sock)

    def connect_unix_socket(
        self, path: str, timeout: typing.Optional[float] = None
    ) -> NetworkStream:  # pragma: nocover
        if sys.platform == "win32":
            raise RuntimeError("Cannot connect to UNIX socket on a non UNIX system")
            
        exc_map: ExceptionMapping = {
            socket.timeout: ConnectTimeout,
            OSError: ConnectError,
        }
        with map_exceptions(exc_map):
            sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
            sock.settimeout(timeout)
            sock.connect(path)
        return SyncStream(sock)

[tomchristie]

Seems like a good idea.