From 4eb358863b3797af1e5a6712b02a01f4a7fe985d Mon Sep 17 00:00:00 2001
From: goingforstudying-ctrl <goingforstudying@gmail.com>
Date: Tue, 2 Jun 2026 19:33:02 -0400
Subject: [PATCH] fix(connector): resolve race condition in
 TCPConnector.close() (#12787)

---
 CHANGES/12497.bugfix.rst |  1 +
 CONTRIBUTORS.txt         |  1 +
 aiohttp/connector.py     |  7 ++++--
 tests/test_connector.py  | 46 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 53 insertions(+), 2 deletions(-)
 create mode 100644 CHANGES/12497.bugfix.rst

diff --git a/CHANGES/12497.bugfix.rst b/CHANGES/12497.bugfix.rst
new file mode 100644
index 00000000000..7fd5883ccbd
--- /dev/null
+++ b/CHANGES/12497.bugfix.rst
@@ -0,0 +1 @@
+Fixed a race condition in :py:class:`~aiohttp.TCPConnector` where closing the connector while a DNS resolution was in-flight could raise :py:exc:`AttributeError` instead of :py:exc:`~aiohttp.ClientConnectionError` -- by :user:`goingforstudying-ctrl`.
diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index d13a189129a..2aaa0a02403 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -153,6 +153,7 @@ Gary Wilson Jr.
 Gene Hoffman
 Gennady Andreyev
 Georges Dubus
+goingforstudying-ctrl
 Greg Holt
 Gregory Haynes
 Grigoriy Soldatov
diff --git a/aiohttp/connector.py b/aiohttp/connector.py
index 3f73b1f6418..6e70b3a28a2 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()):
@@ -1062,6 +1062,9 @@ async def _resolve_host(
                 for trace in traces:
                     await trace.send_dns_resolvehost_start(host)
 
+            if self._closed:
+                raise ClientConnectionError("Connector is closed")
+
             res = await self._resolver.resolve(host, port, family=self._family)
 
             if traces:
diff --git a/tests/test_connector.py b/tests/test_connector.py
index a246bd38b18..0b1cbcff03e 100644
--- a/tests/test_connector.py
+++ b/tests/test_connector.py
@@ -4698,3 +4698,49 @@ async def test_connect_tunnel_connection_release() -> None:
 
     # Clean up to avoid resource warning
     conn.close()
+
+
+async def test_tcp_connector_close_race_condition() -> None:
+    """Test closing TCPConnector while DNS resolution is in-flight."""
+    loop = asyncio.get_running_loop()
+    resolve_started = loop.create_future()
+    close_started = loop.create_future()
+
+    class FakeResolver(AbstractResolver):
+        async def resolve(
+            self, host: str, port: int = 0, family: int = socket.AF_INET
+        ) -> list[ResolveResult]:
+            resolve_started.set_result(None)
+            await close_started
+            return [
+                {
+                    "hostname": host,
+                    "host": host,
+                    "port": port,
+                    "family": family,
+                    "proto": 0,
+                    "flags": socket.AI_NUMERICHOST,
+                }
+            ]
+
+        async def close(self) -> None:
+            assert False
+
+    connector = TCPConnector(use_dns_cache=False, resolver=FakeResolver())
+
+    async def resolve_host() -> None:
+        # The in-flight resolve should complete normally since close()
+        # happens after the resolver returns
+        result = await connector._resolve_host("localhost", 80)
+        assert len(result) == 1
+
+    async def close_connector() -> None:
+        await resolve_started
+        close_started.set_result(None)
+        await connector.close()
+
+    await asyncio.gather(resolve_host(), close_connector())
+
+    # After close, new resolves should raise ClientConnectionError
+    with pytest.raises(aiohttp.ClientConnectionError, match="Connector is closed"):
+        await connector._resolve_host("localhost", 80)