GH-86508: skip binding to local addresses of different family in `asy…

…ncio.open_connection` (#100615)

Lib/asyncio/base_events.py

@@ -961,7 +961,10 @@ async def _connect_sock(self, exceptions, addr_info, local_addr_infos=None):
             sock = socket.socket(family=family, type=type_, proto=proto)
             sock.setblocking(False)
             if local_addr_infos is not None:
-                for _, _, _, _, laddr in local_addr_infos:
+                for lfamily, _, _, _, laddr in local_addr_infos:
+                    # skip local addresses of different family
+                    if lfamily != family:
+                        continue
                     try:
                         sock.bind(laddr)
                         break
@@ -974,7 +977,10 @@ async def _connect_sock(self, exceptions, addr_info, local_addr_infos=None):
                         exc = OSError(exc.errno, msg)
                         my_exceptions.append(exc)
                 else:  # all bind attempts failed
-                    raise my_exceptions.pop()
+                    if my_exceptions:
+                        raise my_exceptions.pop()
+                    else:
+                        raise OSError(f"no matching local address with {family=} found")
             await self.sock_connect(sock, address)
             return sock
         except OSError as exc:

Lib/test/test_asyncio/test_events.py

@@ -670,6 +670,47 @@ def test_create_connection_local_addr(self):
             self.assertEqual(port, expected)
             tr.close()
 
+    def test_create_connection_local_addr_skip_different_family(self):
+        # See https://github.com/python/cpython/issues/86508
+        port1 = socket_helper.find_unused_port()
+        port2 = socket_helper.find_unused_port()
+        getaddrinfo_orig = self.loop.getaddrinfo
+
+        async def getaddrinfo(host, port, *args, **kwargs):
+            if port == port2:
+                return [(socket.AF_INET6, socket.SOCK_STREAM, 0, '', ('::1', 0, 0, 0)),
+                        (socket.AF_INET, socket.SOCK_STREAM, 0, '', ('127.0.0.1', 0))]
+            return await getaddrinfo_orig(host, port, *args, **kwargs)
+
+        self.loop.getaddrinfo = getaddrinfo
+
+        f = self.loop.create_connection(
+            lambda: MyProto(loop=self.loop),
+            'localhost', port1, local_addr=('localhost', port2))
+
+        with self.assertRaises(OSError):
+            self.loop.run_until_complete(f)
+
+    def test_create_connection_local_addr_nomatch_family(self):
+        # See https://github.com/python/cpython/issues/86508
+        port1 = socket_helper.find_unused_port()
+        port2 = socket_helper.find_unused_port()
+        getaddrinfo_orig = self.loop.getaddrinfo
+
+        async def getaddrinfo(host, port, *args, **kwargs):
+            if port == port2:
+                return [(socket.AF_INET6, socket.SOCK_STREAM, 0, '', ('::1', 0, 0, 0))]
+            return await getaddrinfo_orig(host, port, *args, **kwargs)
+
+        self.loop.getaddrinfo = getaddrinfo
+
+        f = self.loop.create_connection(
+            lambda: MyProto(loop=self.loop),
+            'localhost', port1, local_addr=('localhost', port2))
+
+        with self.assertRaises(OSError):
+            self.loop.run_until_complete(f)
+
     def test_create_connection_local_addr_in_use(self):
         with test_utils.run_test_server() as httpd:
             f = self.loop.create_connection(

Misc/NEWS.d/next/Library/2022-12-30-07-49-08.gh-issue-86508.nGZDzC.rst

@@ -0,0 +1 @@
+Fix :func:`asyncio.open_connection` to skip binding to local addresses of different family. Patch by Kumar Aditya.