Avoid dual-stack

OpenBSD doesn't support dual stack, that makes this broken on machine
which hasn't got IPv6.

Anyway, a machine which has IPv6, still, can't access IPv4 hosts.

src/aioquic/asyncio/client.py

@@ -47,13 +47,6 @@ async def connect(
     * ``local_port`` is the UDP port number that this client wants to bind.
     """
     loop = asyncio.get_event_loop()
-    local_host = "::"
-
-    # lookup remote address
-    infos = await loop.getaddrinfo(host, port, type=socket.SOCK_DGRAM)
-    addr = infos[0][4]
-    if len(addr) == 2:
-        addr = ("::ffff:" + addr[0], addr[1], 0, 0)
 
     # prepare QUIC connection
     if configuration is None:
@@ -66,16 +59,28 @@ async def connect(
         token_handler=token_handler,
     )
 
-    # explicitly enable IPv4/IPv6 dual stack
-    sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
+    # lookup remote address
+    infos = await loop.getaddrinfo(host, port, type=socket.SOCK_DGRAM, flags=socket.AI_ADDRCONFIG)
+
+    addr = infos[0][4]
+    # addr is 2-tuple for AF_INET and 4-tuple for AF_INET6
+    if len(addr) == 2:
+        local_tuple = ("0.0.0.0", local_port)
+        sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    elif len(addr) == 4:
+        local_tuple = ("::", local_port, 0, 0)
+        sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
+    else:
+        raise Exception("Unsupported response from getaddrinfo")
+
     completed = False
     try:
-        sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
-        sock.bind((local_host, local_port, 0, 0))
+        sock.bind(local_tuple)
         completed = True
     finally:
         if not completed:
             sock.close()
+
     # connect
     transport, protocol = await loop.create_datagram_endpoint(
         lambda: create_protocol(connection, stream_handler=stream_handler),