Fix handling of connection timeouts in outgoing http requests (#8400)

* Remove `on_timeout_cancel` from `timeout_deferred`

The `on_timeout_cancel` param to `timeout_deferred` wasn't always called on a
timeout (in particular if the canceller raised an exception), so it was
unreliable. It was also only used in one place, and to be honest it's easier to
do what it does a different way.

* Fix handling of connection timeouts in outgoing http requests

Turns out that if we get a timeout during connection, then a different
exception is raised, which wasn't always handled correctly.

To fix it, catch the exception in SimpleHttpClient and turn it into a
RequestTimedOutError (which is already a documented exception).

Also add a description to RequestTimedOutError so that we can see which stage
it failed at.

* Fix incorrect handling of timeouts reading federation responses

This was trapping the wrong sort of TimeoutError, so was never being hit.

The effect was relatively minor, but we should fix this so that it does the
expected thing.

* Fix inconsistent handling of `timeout` param between methods

`get_json`, `put_json` and `delete_json` were applying a different timeout to
the response body to `post_json`; bring them in line and test.

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>
Co-authored-by: Erik Johnston <erik@matrix.org>

synapse/http/client.py

@@ -13,7 +13,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
 import logging
 import urllib
 from io import BytesIO
@@ -38,7 +37,7 @@ from zope.interface import implementer, provider
 
 from OpenSSL import SSL
 from OpenSSL.SSL import VERIFY_NONE
-from twisted.internet import defer, protocol, ssl
+from twisted.internet import defer, error as twisted_error, protocol, ssl
 from twisted.internet.interfaces import (
     IReactorPluggableNameResolver,
     IResolutionReceiver,
@@ -46,17 +45,18 @@ from twisted.internet.interfaces import (
 from twisted.internet.task import Cooperator
 from twisted.python.failure import Failure
 from twisted.web._newclient import ResponseDone
-from twisted.web.client import Agent, HTTPConnectionPool, readBody
+from twisted.web.client import (
+    Agent,
+    HTTPConnectionPool,
+    ResponseNeverReceived,
+    readBody,
+)
 from twisted.web.http import PotentialDataLoss
 from twisted.web.http_headers import Headers
 from twisted.web.iweb import IResponse
 
 from synapse.api.errors import Codes, HttpResponseException, SynapseError
-from synapse.http import (
-    QuieterFileBodyProducer,
-    cancelled_to_request_timed_out_error,
-    redact_uri,
-)
+from synapse.http import QuieterFileBodyProducer, RequestTimedOutError, redact_uri
 from synapse.http.proxyagent import ProxyAgent
 from synapse.logging.context import make_deferred_yieldable
 from synapse.logging.opentracing import set_tag, start_active_span, tags
@@ -332,8 +332,6 @@ class SimpleHttpClient:
             RequestTimedOutError if the request times out before the headers are read
 
         """
-        # A small wrapper around self.agent.request() so we can easily attach
-        # counters to it
         outgoing_requests_counter.labels(method).inc()
 
         # log request but strip `access_token` (AS requests for example include this)
@@ -362,15 +360,17 @@ class SimpleHttpClient:
                     data=body_producer,
                     headers=headers,
                     **self._extra_treq_args
-                )
+                )  # type: defer.Deferred
+
                 # we use our own timeout mechanism rather than treq's as a workaround
                 # for https://twistedmatrix.com/trac/ticket/9534.
                 request_deferred = timeout_deferred(
-                    request_deferred,
-                    60,
-                    self.hs.get_reactor(),
-                    cancelled_to_request_timed_out_error,
+                    request_deferred, 60, self.hs.get_reactor(),
                 )
+
+                # turn timeouts into RequestTimedOutErrors
+                request_deferred.addErrback(_timeout_to_request_timed_out_error)
+
                 response = await make_deferred_yieldable(request_deferred)
 
                 incoming_responses_counter.labels(method, response.code).inc()
@@ -410,7 +410,7 @@ class SimpleHttpClient:
             parsed json
 
         Raises:
-            RequestTimedOutException: if there is a timeout before the response headers
+            RequestTimedOutError: if there is a timeout before the response headers
                are received. Note there is currently no timeout on reading the response
                body.
 
@@ -461,7 +461,7 @@ class SimpleHttpClient:
             parsed json
 
         Raises:
-            RequestTimedOutException: if there is a timeout before the response headers
+            RequestTimedOutError: if there is a timeout before the response headers
                are received. Note there is currently no timeout on reading the response
                body.
 
@@ -506,7 +506,7 @@ class SimpleHttpClient:
         Returns:
             Succeeds when we get a 2xx HTTP response, with the HTTP body as JSON.
         Raises:
-            RequestTimedOutException: if there is a timeout before the response headers
+            RequestTimedOutError: if there is a timeout before the response headers
                are received. Note there is currently no timeout on reading the response
                body.
 
@@ -538,7 +538,7 @@ class SimpleHttpClient:
         Returns:
             Succeeds when we get a 2xx HTTP response, with the HTTP body as JSON.
         Raises:
-             RequestTimedOutException: if there is a timeout before the response headers
+             RequestTimedOutError: if there is a timeout before the response headers
                are received. Note there is currently no timeout on reading the response
                body.
 
@@ -586,7 +586,7 @@ class SimpleHttpClient:
             Succeeds when we get a 2xx HTTP response, with the
             HTTP body as bytes.
         Raises:
-            RequestTimedOutException: if there is a timeout before the response headers
+            RequestTimedOutError: if there is a timeout before the response headers
                are received. Note there is currently no timeout on reading the response
                body.
 
@@ -631,7 +631,7 @@ class SimpleHttpClient:
             headers, absolute URI of the response and HTTP response code.
 
         Raises:
-            RequestTimedOutException: if there is a timeout before the response headers
+            RequestTimedOutError: if there is a timeout before the response headers
                are received. Note there is currently no timeout on reading the response
                body.
 
@@ -684,6 +684,18 @@ class SimpleHttpClient:
         )
 
 
+def _timeout_to_request_timed_out_error(f: Failure):
+    if f.check(twisted_error.TimeoutError, twisted_error.ConnectingCancelledError):
+        # The TCP connection has its own timeout (set by the 'connectTimeout' param
+        # on the Agent), which raises twisted_error.TimeoutError exception.
+        raise RequestTimedOutError("Timeout connecting to remote server")
+    elif f.check(defer.TimeoutError, ResponseNeverReceived):
+        # this one means that we hit our overall timeout on the request
+        raise RequestTimedOutError("Timeout waiting for response from remote server")
+
+    return f
+
+
 # XXX: FIXME: This is horribly copy-pasted from matrixfederationclient.
 # The two should be factored out.