Close the socket if there's a failure in start_connection()

CHANGES/10464.bugfix.rst

@@ -0,0 +1 @@
+Changed connection creation to explicitly close sockets if an exception is raised in the event loop's ``create_connection`` method.

CONTRIBUTORS.txt

@@ -43,6 +43,7 @@ Andrej Antonov
 Andrew Leech
 Andrew Lytvyn
 Andrew Svetlov
+Andrew Top
 Andrew Zhou
 Andrii Soldatenko
 Anes Abismail

aiohttp/connector.py

@@ -1101,6 +1101,7 @@ async def _wrap_create_connection(
         client_error: Type[Exception] = ClientConnectorError,
         **kwargs: Any,
     ) -> Tuple[asyncio.Transport, ResponseHandler]:
+        sock = None
         try:
             async with ceil_timeout(
                 timeout.sock_connect, ceil_threshold=timeout.ceil_threshold
@@ -1112,7 +1113,11 @@ async def _wrap_create_connection(
                     interleave=self._interleave,
                     loop=self._loop,
                 )
-                return await self._loop.create_connection(*args, **kwargs, sock=sock)
+                connection = await self._loop.create_connection(
+                    *args, **kwargs, sock=sock
+                )
+                sock = None
+                return connection
         except cert_errors as exc:
             raise ClientConnectorCertificateError(req.connection_key, exc) from exc
         except ssl_errors as exc:
@@ -1121,6 +1126,12 @@ async def _wrap_create_connection(
             if exc.errno is None and isinstance(exc, asyncio.TimeoutError):
                 raise
             raise client_error(req.connection_key, exc) from exc
+        finally:
+            if sock is not None:
+                # Will be hit if an exception is thrown before the event loop takes the socket.
+                # In that case, proactively close the socket to guard against event loop leaks.
+                # For example, see https://github.com/MagicStack/uvloop/issues/653.
+                sock.close()
 
     def _warn_about_tls_in_tls(
         self,

tests/conftest.py

@@ -222,6 +222,7 @@ def start_connection() -> Iterator[mock.Mock]:
         "aiohttp.connector.aiohappyeyeballs.start_connection",
         autospec=True,
         spec_set=True,
+        return_value=mock.create_autospec(socket.socket, spec_set=True, instance=True),
     ) as start_connection_mock:
         yield start_connection_mock
 

tests/test_connector.py

@@ -646,6 +646,27 @@ async def test_tcp_connector_certificate_error(
     await conn.close()
 
 
+async def test_tcp_connector_closes_socket_on_error(
+    loop: asyncio.AbstractEventLoop, start_connection: mock.AsyncMock
+) -> None:
+    req = ClientRequest("GET", URL("https://127.0.0.1:443"), loop=loop)
+
+    conn = aiohttp.TCPConnector()
+    with mock.patch.object(
+        conn._loop,
+        "create_connection",
+        autospec=True,
+        spec_set=True,
+        side_effect=ValueError,
+    ):
+        with pytest.raises(ValueError):
+            await conn.connect(req, [], ClientTimeout())
+
+        assert start_connection.return_value.close.called
+
+    await conn.close()
+
+
 async def test_tcp_connector_server_hostname_default(
     loop: asyncio.AbstractEventLoop, start_connection: mock.AsyncMock
 ) -> None:

tests/test_proxy.py

@@ -216,6 +216,7 @@ async def make_conn() -> aiohttp.TCPConnector:
         "aiohttp.connector.aiohappyeyeballs.start_connection",
         autospec=True,
         spec_set=True,
+        return_value=mock.create_autospec(socket.socket, spec_set=True, instance=True),
     )
     def test_proxy_connection_error(self, start_connection: mock.Mock) -> None:
         async def make_conn() -> aiohttp.TCPConnector: