Check if ipv6 is enabled, when processing socket address info

CHANGES/5901.bugfix

@@ -0,0 +1,4 @@
+Fix the error in handling the return value of `getaddrinfo`.
+`getaddrinfo` will return an `(int, bytes)` tuple, if CPython could not handle the address family.
+It will cause a index out of range error in aiohttp. For example, if user compile CPython with
+`--disable-ipv6` option but his system enable the ipv6.

aiohttp/resolver.py

@@ -37,7 +37,9 @@ async def resolve(
 
         hosts = []
         for family, _, proto, _, address in infos:
-            if family == socket.AF_INET6 and address[3]:  # type: ignore[misc]
+            if family == socket.AF_INET6:
+                if not (socket.has_ipv6 and address[3]):  # type: ignore[misc]
+                    continue
                 # This is essential for link-local IPv6 addresses.
                 # LL IPv6 is a VERY rare case. Strictly speaking, we should use
                 # getnameinfo() unconditionally, but performance makes sense.

tests/test_resolver.py

@@ -119,6 +119,30 @@ async def test_threaded_negative_lookup() -> None:
         await resolver.resolve("doesnotexist.bla")
 
 
+async def test_threaded_negative_lookup_with_unknown_result() -> None:
+    loop = Mock()
+
+    # If compile CPython with `--disable-ipv6` option,
+    # we will get an (int, bytes) tuple, instead of a Exception.
+    async def unknown_addrinfo(*args: Any, **kwargs: Any) -> List[Any]:
+        return [
+            (
+                socket.AF_INET6,
+                socket.SOCK_STREAM,
+                6,
+                "",
+                (10, b"\x01\xbb\x00\x00\x00\x00*\x04NB\x00\x1a\x00\x00"),
+            )
+        ]
+
+    loop.getaddrinfo = unknown_addrinfo
+    resolver = ThreadedResolver()
+    resolver._loop = loop
+    with patch("socket.has_ipv6", False):
+        res = await resolver.resolve("www.python.org")
+    assert len(res) == 0
+
+
 async def test_close_for_threaded_resolver(loop: Any) -> None:
     resolver = ThreadedResolver()
     await resolver.close()