Fix TLSListener.handle_handshake_error on asyncio failing to log th…

…e error on CPython (#609)

Fixes #608.

docs/versionhistory.rst

@@ -12,6 +12,9 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
   message) on asyncio to determine if a cancellation exception should be swallowed on scope exit,
   to combat issues where third party libraries catch the ``CancelledError`` and raise another, thus
   erasing the original cancel message
+- Worked around a `CPython bug <https://github.com/python/cpython/issues/108668>`_ that
+  caused ``TLSListener.handle_handshake_error()`` on asyncio to log ``"NoneType: None"``
+  instead of the error (PR by Ganden Schaffner)
 
 **4.0.0rc1**
 

src/anyio/streams/tls.py

@@ -286,7 +286,13 @@ async def handle_handshake_error(exc: BaseException, stream: AnyByteStream) -> N
 
         # Log all except cancellation exceptions
         if not isinstance(exc, get_cancelled_exc_class()):
-            logging.getLogger(__name__).exception("Error during TLS handshake")
+            # CPython (as of 3.11.5) returns incorrect `sys.exc_info()` here when using
+            # any asyncio implementation, so we explicitly pass the exception to log
+            # (https://github.com/python/cpython/issues/108668). Trio does not have this
+            # issue because it works around the CPython bug.
+            logging.getLogger(__name__).exception(
+                "Error during TLS handshake", exc_info=exc
+            )
 
         # Only reraise base exceptions and cancellation exceptions
         if not isinstance(exc, Exception) or isinstance(exc, get_cancelled_exc_class()):

tests/streams/test_tls.py

@@ -398,7 +398,9 @@ async def test_default_context_ignore_unexpected_eof_flag_off(
 
 class TestTLSListener:
     @skip_on_broken_openssl
-    async def test_handshake_fail(self, server_context: ssl.SSLContext) -> None:
+    async def test_handshake_fail(
+        self, server_context: ssl.SSLContext, caplog: pytest.LogCaptureFixture
+    ) -> None:
         def handler(stream: object) -> NoReturn:
             pytest.fail("This function should never be called in this scenario")
 
@@ -411,6 +413,13 @@ async def handle_handshake_error(
             ) -> None:
                 nonlocal exception
                 await TLSListener.handle_handshake_error(exc, stream)
+
+                # Regression test for #608
+                assert len(caplog.records) == 1
+                logged_exc_info = caplog.records[0].exc_info
+                logged_exc = logged_exc_info[1] if logged_exc_info is not None else None
+                assert logged_exc is exc
+
                 assert isinstance(stream, SocketStream)
                 exception = exc
                 event.set()