Enable dual-stack on all platform with exception for OpenBSD

src/aioquic/asyncio/client.py

@@ -1,7 +1,8 @@
 import asyncio
 import socket
+import sys
 from contextlib import asynccontextmanager
-from typing import AsyncGenerator, Callable, Optional, cast
+from typing import AsyncGenerator, Callable, Optional, Tuple, Union, cast
 
 from ..quic.configuration import QuicConfiguration
 from ..quic.connection import QuicConnection, QuicTokenHandler
@@ -59,12 +60,25 @@ async def connect(
         token_handler=token_handler,
     )
 
+    # OpenBSD well known to not support dual-stack
+    dual_stack = not sys.platform.startswith("openbsd")
+
+    # Use AI_ADDRCONFIG on platforms which doesn't support dual-stack
+    flags = 0
+    if not dual_stack:
+        flags = socket.AI_ADDRCONFIG
+
     # lookup remote address
-    infos = await loop.getaddrinfo(host, port, type=socket.SOCK_DGRAM, flags=socket.AI_ADDRCONFIG)
+    infos = await loop.getaddrinfo(host, port, type=socket.SOCK_DGRAM, flags=flags)
 
+    local_tuple: Union[Tuple[str, int], Tuple[str, int, int, int]]
     addr = infos[0][4]
     # addr is 2-tuple for AF_INET and 4-tuple for AF_INET6
-    if len(addr) == 2:
+    if dual_stack and len(addr) == 2:
+        addr = ("::ffff:" + addr[0], addr[1], 0, 0)
+        local_tuple = ("::", local_port, 0, 0)
+        sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
+    elif len(addr) == 2:
         local_tuple = ("0.0.0.0", local_port)
         sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
     elif len(addr) == 4:
@@ -75,6 +89,8 @@ async def connect(
 
     completed = False
     try:
+        if dual_stack:
+            sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
         sock.bind(local_tuple)
         completed = True
     finally: