Print stacktrace when catching TimeoutError (#3414)

CHANGES/3414.bugfix

@@ -0,0 +1,2 @@
+Fix `asyncio.TimeoutError` stack trace not logged, when it is caught
+in the handler.

CONTRIBUTORS.txt

@@ -172,6 +172,7 @@ Paulius Šileikis
 Paulus Schoutsen
 Pavel Kamaev
 Pavel Polyakov
+Pawel Kowalski
 Pawel Miech
 Pepe Osca
 Philipp A.

aiohttp/web_protocol.py

@@ -408,8 +408,8 @@ async def start(self) -> None:
  except asyncio.CancelledError:
  self.log_debug('Ignored premature client disconnection')
  break
- except asyncio.TimeoutError:
- self.log_debug('Request handler timed out.')
+ except asyncio.TimeoutError as exc:
+ self.log_debug('Request handler timed out.', exc_info=exc)
  resp = self.handle_error(request, 504)
  except Exception as exc:
  resp = self.handle_error(request, 500, exc)

tests/test_web_protocol.py

@@ -581,6 +581,17 @@ async def test_handle_500(srv, buf, transport, request_handler) -> None:
  assert b'500 Internal Server Error' in buf
 
 
+async def test_handle_504(srv, buf, request_handler) -> None:
+ request_handler.side_effect = asyncio.TimeoutError
+
+ srv.data_received(
+ b'GET / HTTP/1.0\r\n'
+ b'Host: example.com\r\n\r\n')
+ await srv._task_handler
+
+ assert b'504 Gateway Timeout' in buf
+
+
 async def test_keep_alive(make_srv, transport, ceil) -> None:
  loop = asyncio.get_event_loop()
  srv = make_srv(keepalive_timeout=0.05)

tests/test_web_server.py

@@ -53,7 +53,7 @@ async def handler(request):
  assert resp.status == 504
 
  await resp.text()
- logger.debug.assert_called_with("Request handler timed out.")
+ logger.debug.assert_called_with("Request handler timed out.", exc_info=exc)
 
 
 async def test_raw_server_do_not_swallow_exceptions(aiohttp_raw_server,