Cache dns lookups, and use the cache if we fail to lookup servers later

tests/test_dns.py

@@ -0,0 +1,115 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014-2016 OpenMarket Ltd
+#
+# 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 . import unittest
+from twisted.internet import defer
+from twisted.names import dns, error
+
+from mock import Mock
+
+from synapse.http.endpoint import resolve_service
+
+
+class DnsTestCase(unittest.TestCase):
+
+    @defer.inlineCallbacks
+    def test_resolve(self):
+        dns_client_mock = Mock()
+
+        service_name = "test_service.examle.com"
+        host_name = "example.com"
+        ip_address = "127.0.0.1"
+
+        answer_srv = dns.RRHeader(
+            type=dns.SRV,
+            payload=dns.Record_SRV(
+                target=host_name,
+            )
+        )
+
+        answer_a = dns.RRHeader(
+            type=dns.A,
+            payload=dns.Record_A(
+                address=ip_address,
+            )
+        )
+
+        dns_client_mock.lookupService.return_value = ([answer_srv], None, None)
+        dns_client_mock.lookupAddress.return_value = ([answer_a], None, None)
+
+        cache = {}
+
+        servers = yield resolve_service(
+            service_name, dns_client=dns_client_mock, cache=cache
+        )
+
+        dns_client_mock.lookupService.assert_called_once_with(service_name)
+        dns_client_mock.lookupAddress.assert_called_once_with(host_name)
+
+        self.assertEquals(len(servers), 1)
+        self.assertEquals(servers, cache[service_name])
+        self.assertEquals(servers[0].host, ip_address)
+
+    @defer.inlineCallbacks
+    def test_from_cache(self):
+        dns_client_mock = Mock()
+        dns_client_mock.lookupService.return_value = defer.fail(error.DNSServerError())
+
+        service_name = "test_service.examle.com"
+
+        cache = {
+            service_name: [object()]
+        }
+
+        servers = yield resolve_service(
+            service_name, dns_client=dns_client_mock, cache=cache
+        )
+
+        dns_client_mock.lookupService.assert_called_once_with(service_name)
+
+        self.assertEquals(len(servers), 1)
+        self.assertEquals(servers, cache[service_name])
+
+    @defer.inlineCallbacks
+    def test_empty_cache(self):
+        dns_client_mock = Mock()
+
+        dns_client_mock.lookupService.return_value = defer.fail(error.DNSServerError())
+
+        service_name = "test_service.examle.com"
+
+        cache = {}
+
+        with self.assertRaises(error.DNSServerError):
+            yield resolve_service(
+                service_name, dns_client=dns_client_mock, cache=cache
+            )
+
+    @defer.inlineCallbacks
+    def test_name_error(self):
+        dns_client_mock = Mock()
+
+        dns_client_mock.lookupService.return_value = defer.fail(error.DNSNameError())
+
+        service_name = "test_service.examle.com"
+
+        cache = {}
+
+        servers = yield resolve_service(
+            service_name, dns_client=dns_client_mock, cache=cache
+        )
+
+        self.assertEquals(len(servers), 0)
+        self.assertEquals(len(cache), 0)