Downgrade warning on client disconnect to INFO (#7928)

Clients disconnecting before we finish processing the request happens from time
to time. We don't need to yell about it

changelog.d/7928.misc

@@ -0,0 +1 @@
+When a client disconnects, don't log it as 'Error processing request'.

synapse/http/site.py

@@ -215,9 +215,7 @@ def connectionLost(self, reason):
         # It's useful to log it here so that we can get an idea of when
         # the client disconnects.
         with PreserveLoggingContext(self.logcontext):
-            logger.warning(
-                "Error processing request %r: %s %s", self, reason.type, reason.value
-            )
+            logger.info("Connection from client lost before response was sent")
 
             if not self._is_processing:
                 self._finished_processing()

tests/test_server.py

@@ -12,26 +12,20 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import logging
 import re
-from io import StringIO
 
 from twisted.internet.defer import Deferred
-from twisted.python.failure import Failure
-from twisted.test.proto_helpers import AccumulatingProtocol
 from twisted.web.resource import Resource
-from twisted.web.server import NOT_DONE_YET
 
 from synapse.api.errors import Codes, RedirectException, SynapseError
 from synapse.config.server import parse_listener_def
 from synapse.http.server import DirectServeHtmlResource, JsonResource, OptionsResource
-from synapse.http.site import SynapseSite, logger
+from synapse.http.site import SynapseSite
 from synapse.logging.context import make_deferred_yieldable
 from synapse.util import Clock
 
 from tests import unittest
 from tests.server import (
-    FakeTransport,
     ThreadedMemoryReactorClock,
     make_request,
     render,
@@ -318,54 +312,3 @@ def callback(request, **kwargs):
         self.assertEqual(location_headers, [b"/no/over/there"])
         cookies_headers = [v for k, v in headers if k == b"Set-Cookie"]
         self.assertEqual(cookies_headers, [b"session=yespls"])
-
-
-class SiteTestCase(unittest.HomeserverTestCase):
-    def test_lose_connection(self):
-        """
-        We log the URI correctly redacted when we lose the connection.
-        """
-
-        class HangingResource(Resource):
-            """
-            A Resource that strategically hangs, as if it were processing an
-            answer.
-            """
-
-            def render(self, request):
-                return NOT_DONE_YET
-
-        # Set up a logging handler that we can inspect afterwards
-        output = StringIO()
-        handler = logging.StreamHandler(output)
-        logger.addHandler(handler)
-        old_level = logger.level
-        logger.setLevel(10)
-        self.addCleanup(logger.setLevel, old_level)
-        self.addCleanup(logger.removeHandler, handler)
-
-        # Make a resource and a Site, the resource will hang and allow us to
-        # time out the request while it's 'processing'
-        base_resource = Resource()
-        base_resource.putChild(b"", HangingResource())
-        site = SynapseSite(
-            "test", "site_tag", self.hs.config.listeners[0], base_resource, "1.0"
-        )
-
-        server = site.buildProtocol(None)
-        client = AccumulatingProtocol()
-        client.makeConnection(FakeTransport(server, self.reactor))
-        server.makeConnection(FakeTransport(client, self.reactor))
-
-        # Send a request with an access token that will get redacted
-        server.dataReceived(b"GET /?access_token=bar HTTP/1.0\r\n\r\n")
-        self.pump()
-
-        # Lose the connection
-        e = Failure(Exception("Failed123"))
-        server.connectionLost(e)
-        handler.flush()
-
-        # Our access token is redacted and the failure reason is logged.
-        self.assertIn("/?access_token=<redacted>", output.getvalue())
-        self.assertIn("Failed123", output.getvalue())