PYTHON-5867 - Close sockets on interruption or cancellation during async connection creation

pymongo/pool_shared.py

@@ -182,7 +182,8 @@ async def _async_create_connection(address: _Address, options: PoolOptions) -> s
             sock.setblocking(False)
             await asyncio.get_running_loop().sock_connect(sock, host)
             return sock
-        except OSError:
+        except BaseException:
+            # Protect against cancellation or interruption where the raw socket would otherwise leak
             sock.close()
             raise
 
@@ -231,6 +232,10 @@ async def _async_create_connection(address: _Address, options: PoolOptions) -> s
         except OSError as e:
             sock.close()
             err = e  # type: ignore[assignment]
+        except BaseException:
+            # Protect against cancellation or interruption where the raw socket would otherwise leak
+            sock.close()
+            raise
 
     if err is not None:
         raise err
@@ -282,19 +287,25 @@ async def _async_configured_socket(
         # mismatch, will be turned into ServerSelectionTimeoutErrors later.
         details = _get_timeout_details(options)
         _raise_connection_failure(address, exc, "SSL handshake failed: ", timeout_details=details)
-    if (
-        ssl_context.verify_mode
-        and not ssl_context.check_hostname
-        and not options.tls_allow_invalid_hostnames
-    ):
-        try:
+    except BaseException:
+        # Protect against cancellation or interruption where the raw socket would otherwise leak
+        sock.close()
+        raise
+    try:
+        if (
+            ssl_context.verify_mode
+            and not ssl_context.check_hostname
+            and not options.tls_allow_invalid_hostnames
+        ):
             ssl.match_hostname(ssl_sock.getpeercert(), hostname=host)  # type:ignore[attr-defined, unused-ignore]
-        except _CertificateError:
-            ssl_sock.close()
-            raise
 
-    ssl_sock.settimeout(options.socket_timeout)
-    return ssl_sock
+        ssl_sock.settimeout(options.socket_timeout)
+        return ssl_sock
+    except BaseException:
+        # Protect against cancellation, _CertificateError, or interruption
+        # where the raw socket would otherwise leak.
+        ssl_sock.close()
+        raise
 
 
 async def _configured_protocol_interface(
@@ -337,18 +348,19 @@ async def _configured_protocol_interface(
         # mismatch, will be turned into ServerSelectionTimeoutErrors later.
         details = _get_timeout_details(options)
         _raise_connection_failure(address, exc, "SSL handshake failed: ", timeout_details=details)
-    if (
-        ssl_context.verify_mode
-        and not ssl_context.check_hostname
-        and not options.tls_allow_invalid_hostnames
-    ):
-        try:
+    try:
+        if (
+            ssl_context.verify_mode
+            and not ssl_context.check_hostname
+            and not options.tls_allow_invalid_hostnames
+        ):
             ssl.match_hostname(transport.get_extra_info("peercert"), hostname=host)  # type:ignore[attr-defined,unused-ignore]
-        except _CertificateError:
-            transport.abort()
-            raise
-
-    return AsyncNetworkingInterface((transport, protocol))
+        return AsyncNetworkingInterface((transport, protocol))
+    except BaseException:
+        # Protect against cancellation, _CertificateError, or interruption
+        # where the transport would otherwise leak.
+        transport.abort()
+        raise
 
 
 def _create_connection(address: _Address, options: PoolOptions) -> socket.socket:

test/asynchronous/test_async_cancellation.py

@@ -16,14 +16,18 @@
 from __future__ import annotations
 
 import asyncio
+import socket as _socket
 import sys
 from test.asynchronous.utils import async_get_pool
 from test.utils_shared import delay, one
+from unittest.mock import patch
 
 sys.path[0:0] = [""]
 
 from test.asynchronous import AsyncIntegrationTest, async_client_context, connected
 
+from pymongo import pool_shared
+
 
 class TestAsyncCancellation(AsyncIntegrationTest):
     async def test_async_cancellation_closes_connection(self):
@@ -127,3 +131,41 @@ async def task():
             await task
 
         self.assertTrue(change_stream._closed)
+
+    async def test_cancellation_closes_socket_during_create_connection(self):
+        address = (await async_client_context.host, await async_client_context.port)
+        options = (await async_get_pool(self.client)).opts
+
+        created_sockets: list[_socket.socket] = []
+        real_socket_cls = _socket.socket
+
+        def tracking_socket(*args, **kwargs):
+            s = real_socket_cls(*args, **kwargs)
+            created_sockets.append(s)
+            return s
+
+        loop = asyncio.get_running_loop()
+        started = asyncio.Event()
+        block_forever = asyncio.Event()
+
+        async def slow_sock_connect(sock, addr):
+            started.set()
+            await block_forever.wait()
+
+        with (
+            patch.object(_socket, "socket", tracking_socket),
+            patch.object(loop, "sock_connect", slow_sock_connect),
+        ):
+            task = asyncio.create_task(pool_shared._async_create_connection(address, options))
+            await asyncio.wait_for(started.wait(), timeout=5)
+            task.cancel()
+            with self.assertRaises(asyncio.CancelledError):
+                await task
+
+        self.assertTrue(created_sockets, "expected at least one socket to be created")
+        for sock in created_sockets:
+            self.assertEqual(
+                sock.fileno(),
+                -1,
+                f"socket leaked across cancellation: {sock!r}",
+            )