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>

2 files changed, 188 insertions, 6 deletions

diff --git a/tests/http/test_fedclient.py b/tests/http/test_fedclient.py
index 5604af3795..212484a7fe 100644
--- a/tests/http/test_fedclient.py
+++ b/tests/http/test_fedclient.py
@@ -318,14 +318,14 @@ class FederationClientTests(HomeserverTestCase):
         r = self.successResultOf(d)
         self.assertEqual(r.code, 200)
 
-    def test_client_headers_no_body(self):
+    @parameterized.expand(["get_json", "post_json", "delete_json", "put_json"])
+    def test_timeout_reading_body(self, method_name: str):
         """
         If the HTTP request is connected, but gets no response before being
-        timed out, it'll give a ResponseNeverReceived.
+        timed out, it'll give a RequestSendFailed with can_retry.
         """
-        d = defer.ensureDeferred(
-            self.cl.post_json("testserv:8008", "foo/bar", timeout=10000)
-        )
+        method = getattr(self.cl, method_name)
+        d = defer.ensureDeferred(method("testserv:8008", "foo/bar", timeout=10000))
 
         self.pump()
 
@@ -349,7 +349,9 @@ class FederationClientTests(HomeserverTestCase):
         self.reactor.advance(10.5)
         f = self.failureResultOf(d)
 
-        self.assertIsInstance(f.value, TimeoutError)
+        self.assertIsInstance(f.value, RequestSendFailed)
+        self.assertTrue(f.value.can_retry)
+        self.assertIsInstance(f.value.inner_exception, defer.TimeoutError)
 
     def test_client_requires_trailing_slashes(self):
         """
diff --git a/tests/http/test_simple_client.py b/tests/http/test_simple_client.py
new file mode 100644
index 0000000000..a1cf0862d4
--- /dev/null
+++ b/tests/http/test_simple_client.py
@@ -0,0 +1,180 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# 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.
+from mock import Mock
+
+from netaddr import IPSet
+
+from twisted.internet import defer
+from twisted.internet.error import DNSLookupError
+
+from synapse.http import RequestTimedOutError
+from synapse.http.client import SimpleHttpClient
+from synapse.server import HomeServer
+
+from tests.unittest import HomeserverTestCase
+
+
+class SimpleHttpClientTests(HomeserverTestCase):
+    def prepare(self, reactor, clock, hs: "HomeServer"):
+        # Add a DNS entry for a test server
+        self.reactor.lookups["testserv"] = "1.2.3.4"
+
+        self.cl = hs.get_simple_http_client()
+
+    def test_dns_error(self):
+        """
+        If the DNS lookup returns an error, it will bubble up.
+        """
+        d = defer.ensureDeferred(self.cl.get_json("http://testserv2:8008/foo/bar"))
+        self.pump()
+
+        f = self.failureResultOf(d)
+        self.assertIsInstance(f.value, DNSLookupError)
+
+    def test_client_connection_refused(self):
+        d = defer.ensureDeferred(self.cl.get_json("http://testserv:8008/foo/bar"))
+
+        self.pump()
+
+        # Nothing happened yet
+        self.assertNoResult(d)
+
+        clients = self.reactor.tcpClients
+        self.assertEqual(len(clients), 1)
+        (host, port, factory, _timeout, _bindAddress) = clients[0]
+        self.assertEqual(host, "1.2.3.4")
+        self.assertEqual(port, 8008)
+        e = Exception("go away")
+        factory.clientConnectionFailed(None, e)
+        self.pump(0.5)
+
+        f = self.failureResultOf(d)
+
+        self.assertIs(f.value, e)
+
+    def test_client_never_connect(self):
+        """
+        If the HTTP request is not connected and is timed out, it'll give a
+        ConnectingCancelledError or TimeoutError.
+        """
+        d = defer.ensureDeferred(self.cl.get_json("http://testserv:8008/foo/bar"))
+
+        self.pump()
+
+        # Nothing happened yet
+        self.assertNoResult(d)
+
+        # Make sure treq is trying to connect
+        clients = self.reactor.tcpClients
+        self.assertEqual(len(clients), 1)
+        self.assertEqual(clients[0][0], "1.2.3.4")
+        self.assertEqual(clients[0][1], 8008)
+
+        # Deferred is still without a result
+        self.assertNoResult(d)
+
+        # Push by enough to time it out
+        self.reactor.advance(120)
+        f = self.failureResultOf(d)
+
+        self.assertIsInstance(f.value, RequestTimedOutError)
+
+    def test_client_connect_no_response(self):
+        """
+        If the HTTP request is connected, but gets no response before being
+        timed out, it'll give a ResponseNeverReceived.
+        """
+        d = defer.ensureDeferred(self.cl.get_json("http://testserv:8008/foo/bar"))
+
+        self.pump()
+
+        # Nothing happened yet
+        self.assertNoResult(d)
+
+        # Make sure treq is trying to connect
+        clients = self.reactor.tcpClients
+        self.assertEqual(len(clients), 1)
+        self.assertEqual(clients[0][0], "1.2.3.4")
+        self.assertEqual(clients[0][1], 8008)
+
+        conn = Mock()
+        client = clients[0][2].buildProtocol(None)
+        client.makeConnection(conn)
+
+        # Deferred is still without a result
+        self.assertNoResult(d)
+
+        # Push by enough to time it out
+        self.reactor.advance(120)
+        f = self.failureResultOf(d)
+
+        self.assertIsInstance(f.value, RequestTimedOutError)
+
+    def test_client_ip_range_blacklist(self):
+        """Ensure that Synapse does not try to connect to blacklisted IPs"""
+
+        # Add some DNS entries we'll blacklist
+        self.reactor.lookups["internal"] = "127.0.0.1"
+        self.reactor.lookups["internalv6"] = "fe80:0:0:0:0:8a2e:370:7337"
+        ip_blacklist = IPSet(["127.0.0.0/8", "fe80::/64"])
+
+        cl = SimpleHttpClient(self.hs, ip_blacklist=ip_blacklist)
+
+        # Try making a GET request to a blacklisted IPv4 address
+        # ------------------------------------------------------
+        # Make the request
+        d = defer.ensureDeferred(cl.get_json("http://internal:8008/foo/bar"))
+        self.pump(1)
+
+        # Check that it was unable to resolve the address
+        clients = self.reactor.tcpClients
+        self.assertEqual(len(clients), 0)
+
+        self.failureResultOf(d, DNSLookupError)
+
+        # Try making a POST request to a blacklisted IPv6 address
+        # -------------------------------------------------------
+        # Make the request
+        d = defer.ensureDeferred(
+            cl.post_json_get_json("http://internalv6:8008/foo/bar", {})
+        )
+
+        # Move the reactor forwards
+        self.pump(1)
+
+        # Check that it was unable to resolve the address
+        clients = self.reactor.tcpClients
+        self.assertEqual(len(clients), 0)
+
+        # Check that it was due to a blacklisted DNS lookup
+        self.failureResultOf(d, DNSLookupError)
+
+        # Try making a GET request to a non-blacklisted IPv4 address
+        # ----------------------------------------------------------
+        # Make the request
+        d = defer.ensureDeferred(cl.get_json("http://testserv:8008/foo/bar"))
+
+        # Nothing has happened yet
+        self.assertNoResult(d)
+
+        # Move the reactor forwards
+        self.pump(1)
+
+        # Check that it was able to resolve the address
+        clients = self.reactor.tcpClients
+        self.assertNotEqual(len(clients), 0)
+
+        # Connection will still fail as this IP address does not resolve to anything
+        self.failureResultOf(d, RequestTimedOutError)