Commits on Feb 6, 2024

1. Fix spurious LocalProtocolError errors when processing pipelined requ… …

   …ests
   
   When uvicorn receives a request very soon after it sent the previous
   response, or when it receives pipelined requests, the second request may
   spuriously fail if the ASGI app takes more time to process it than
   uvicorn's `timeout_keep_alive`. This happens because uvicorn arms the
   keep-alive timer as the last step of handling the first request, which
   is after the second request was already received from the network (which
   normally is the only place where uvicorn disarms the keep-alive timer).
   In such cases the timer may fire while uvicorn is still waiting for
   a response from the ASGI app:
   
       Exception in callback H11Protocol.timeout_keep_alive_handler()
       handle: <TimerHandle when=335245.867740771 H11Protocol.timeout_keep_alive_handler()>
       Traceback (most recent call last):
         File "/usr/lib/python3.12/asyncio/events.py", line 84, in _run
           self._context.run(self._callback, *self._args)
         File "venv/lib/python3.12/site-packages/uvicorn/protocols/http/h11_impl.py", line 363, in timeout_keep_alive_handler
           self.conn.send(event)
         File "venv/lib/python3.12/site-packages/h11/_connection.py", line 512, in send
           data_list = self.send_with_data_passthrough(event)
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
         File "venv/lib/python3.12/site-packages/h11/_connection.py", line 537, in send_with_data_passthrough
           self._process_event(self.our_role, event)
         File "venv/lib/python3.12/site-packages/h11/_connection.py", line 272, in _process_event
           self._cstate.process_event(role, type(event), server_switch_event)
         File "venv/lib/python3.12/site-packages/h11/_state.py", line 293, in process_event
           self._fire_event_triggered_transitions(role, _event_type)
         File "venv/lib/python3.12/site-packages/h11/_state.py", line 311, in _fire_event_triggered_transitions
           raise LocalProtocolError(
       h11._util.LocalProtocolError: can't handle event type ConnectionClosed when role=SERVER and state=SEND_RESPONSE
   
   When this happens, the connection is left in the `ERROR` state and when
   a response to the second request is ready to be sent, this fails:
   
       ERROR:    Exception in ASGI application
       Traceback (most recent call last):
         File "venv/lib/python3.12/site-packages/uvicorn/protocols/http/h11_impl.py", line 408, in run_asgi
           result = await app(  # type: ignore[func-returns-value]
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
         File "venv/lib/python3.12/site-packages/uvicorn/middleware/proxy_headers.py", line 84, in __call__
           return await self.app(scope, receive, send)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       (...)
         File "venv/lib/python3.12/site-packages/uvicorn/protocols/http/h11_impl.py", line 490, in send
           output = self.conn.send(event=response)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
         File "venv/lib/python3.12/site-packages/h11/_connection.py", line 512, in send
           data_list = self.send_with_data_passthrough(event)
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
         File "venv/lib/python3.12/site-packages/h11/_connection.py", line 527, in send_with_data_passthrough
           raise LocalProtocolError("Can't send data when our state is ERROR")
       h11._util.LocalProtocolError: Can't send data when our state is ERROR
   
   We fix this by ensuring that the keep-alive timer is disarmed before
   starting to process a pipelined request.
   
   Closes encode#1637

   

   marcinsulikowski committed Feb 6, 2024
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