From dd7ab1ffb1b1259d72447aacfcff66e77d63b756 Mon Sep 17 00:00:00 2001
From: Prashant Mishra <prashant.iecian@gmail.com>
Date: Wed, 13 May 2026 23:11:22 +0530
Subject: [PATCH] Fix TCPConnector.close() race condition with in-flight DNS
 resolution

Fixes #12497

The TCPConnector.close() method had a race condition where the resolver
was closed before marking the connector as closed. This allowed in-flight
DNS resolutions to resume and attempt to use a None resolver, causing
AttributeError instead of the expected ClientConnectionError.

The fix reorders the operations to ensure _closed is set to True
(via super().close()) before closing the resolver. This way, any resumed
DNS resolutions can properly detect the closed state and bail out.

- Reorder close sequence: mark connector closed before closing resolver
- Add regression test for in-flight DNS resolution during close
---
 aiohttp/connector.py    |  4 ++--
 tests/test_connector.py | 26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/aiohttp/connector.py b/aiohttp/connector.py
index 547f9719d39..766513faac9 100644
--- a/aiohttp/connector.py
+++ b/aiohttp/connector.py
@@ -1005,10 +1005,10 @@ async def close(self, *, abort_ssl: bool = False) -> None:
                          - If ssl_shutdown_timeout=0: connections are aborted
                          - If ssl_shutdown_timeout>0: graceful shutdown is performed
         """
-        if self._resolver_owner:
-            await self._resolver.close()
         # Use abort_ssl param if explicitly set, otherwise use ssl_shutdown_timeout default
         await super().close(abort_ssl=abort_ssl or self._ssl_shutdown_timeout == 0)
+        if self._resolver_owner:
+            await self._resolver.close()
 
     def _close_immediately(self, *, abort_ssl: bool = False) -> list[Awaitable[object]]:
         for fut in chain.from_iterable(self._throttle_dns_futures.values()):
diff --git a/tests/test_connector.py b/tests/test_connector.py
index 87d71b999f8..7a08bfcb9fb 100644
--- a/tests/test_connector.py
+++ b/tests/test_connector.py
@@ -1652,6 +1652,32 @@ async def test_tcp_connector_close_resolver() -> None:
         m_resolver.close.assert_awaited_once()
 
 
+async def test_tcp_connector_close_with_in_flight_dns_resolution() -> None:
+    # Regression test for #12497: TCPConnector.close() race with in-flight DNS
+    async def on_dns_start(session, ctx, params):
+        await asyncio.sleep(0)
+
+    trace = aiohttp.TraceConfig()
+    trace.on_dns_resolvehost_start.append(on_dns_start)
+
+    connector = aiohttp.TCPConnector(use_dns_cache=False)
+    session = aiohttp.ClientSession(
+        trace_configs=[trace],
+        connector=connector,
+    )
+
+    # Create a task that will suspend in the trace callback
+    task = asyncio.create_task(session.ws_connect("wss://example.com"))
+    await asyncio.sleep(0)
+
+    # Close the session while the task is suspended
+    await session.close()
+
+    # The task should fail with ClientConnectionError, not AttributeError
+    with pytest.raises((aiohttp.ClientConnectionError, asyncio.CancelledError)):
+        await task
+
+
 async def test_dns_error(make_client_request: _RequestMaker) -> None:
     connector = aiohttp.TCPConnector()
     with mock.patch.object(