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Merge pull request #509 from matrix-org/erikj/dns_cache
Cache dns lookups, and use the cache if we fail to lookup servers later
This commit is contained in:
Erik Johnston
commit
dfe1273d14
@ -17,7 +17,7 @@ from twisted.internet.endpoints import SSL4ClientEndpoint, TCP4ClientEndpoint
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from twisted.internet import defer
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from twisted.internet.error import ConnectError
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from twisted.names import client, dns
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from twisted.names.error import DNSNameError
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from twisted.names.error import DNSNameError, DomainError
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import collections
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import logging
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@ -27,6 +27,14 @@ import random
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logger = logging.getLogger(__name__)
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SERVER_CACHE = {}
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_Server = collections.namedtuple(
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"_Server", "priority weight host port"
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)
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def matrix_federation_endpoint(reactor, destination, ssl_context_factory=None,
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timeout=None):
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"""Construct an endpoint for the given matrix destination.
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@ -73,10 +81,6 @@ class SRVClientEndpoint(object):
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Implements twisted.internet.interfaces.IStreamClientEndpoint.
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"""
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_Server = collections.namedtuple(
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"_Server", "priority weight host port"
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)
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def __init__(self, reactor, service, domain, protocol="tcp",
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default_port=None, endpoint=TCP4ClientEndpoint,
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endpoint_kw_args={}):
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@ -101,32 +105,8 @@ class SRVClientEndpoint(object):
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@defer.inlineCallbacks
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def fetch_servers(self):
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try:
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answers, auth, add = yield client.lookupService(self.service_name)
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except DNSNameError:
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answers = []
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if (len(answers) == 1
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and answers[0].type == dns.SRV
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and answers[0].payload
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and answers[0].payload.target == dns.Name('.')):
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raise ConnectError("Service %s unavailable", self.service_name)
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self.servers = []
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self.used_servers = []
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for answer in answers:
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if answer.type != dns.SRV or not answer.payload:
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continue
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payload = answer.payload
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self.servers.append(self._Server(
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host=str(payload.target),
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port=int(payload.port),
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priority=int(payload.priority),
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weight=int(payload.weight)
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))
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self.servers.sort()
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self.servers = yield resolve_service(self.service_name)
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def pick_server(self):
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if not self.servers:
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@ -170,3 +150,64 @@ class SRVClientEndpoint(object):
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)
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connection = yield endpoint.connect(protocolFactory)
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defer.returnValue(connection)
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@defer.inlineCallbacks
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def resolve_service(service_name, dns_client=client, cache=SERVER_CACHE):
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servers = []
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try:
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try:
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answers, _, _ = yield dns_client.lookupService(service_name)
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except DNSNameError:
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defer.returnValue([])
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if (len(answers) == 1
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and answers[0].type == dns.SRV
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and answers[0].payload
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and answers[0].payload.target == dns.Name('.')):
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raise ConnectError("Service %s unavailable", service_name)
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for answer in answers:
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if answer.type != dns.SRV or not answer.payload:
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continue
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payload = answer.payload
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host = str(payload.target)
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try:
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answers, _, _ = yield dns_client.lookupAddress(host)
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except DNSNameError:
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continue
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ips = [
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answer.payload.dottedQuad()
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for answer in answers
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if answer.type == dns.A and answer.payload
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]
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for ip in ips:
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servers.append(_Server(
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host=ip,
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port=int(payload.port),
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priority=int(payload.priority),
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weight=int(payload.weight)
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))
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servers.sort()
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cache[service_name] = list(servers)
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except DomainError as e:
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# We failed to resolve the name (other than a NameError)
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# Try something in the cache, else rereaise
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cache_entry = cache.get(service_name, None)
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if cache_entry:
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logger.warn(
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"Failed to resolve %r, falling back to cache. %r",
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service_name, e
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)
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servers = list(cache_entry)
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else:
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raise e
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defer.returnValue(servers)
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115
tests/test_dns.py
Normal file
115
tests/test_dns.py
Normal file
@ -0,0 +1,115 @@
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# -*- coding: utf-8 -*-
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# Copyright 2014-2016 OpenMarket Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from . import unittest
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from twisted.internet import defer
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from twisted.names import dns, error
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from mock import Mock
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from synapse.http.endpoint import resolve_service
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class DnsTestCase(unittest.TestCase):
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@defer.inlineCallbacks
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def test_resolve(self):
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dns_client_mock = Mock()
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service_name = "test_service.examle.com"
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host_name = "example.com"
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ip_address = "127.0.0.1"
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answer_srv = dns.RRHeader(
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type=dns.SRV,
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payload=dns.Record_SRV(
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target=host_name,
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)
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)
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answer_a = dns.RRHeader(
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type=dns.A,
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payload=dns.Record_A(
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address=ip_address,
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)
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)
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dns_client_mock.lookupService.return_value = ([answer_srv], None, None)
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dns_client_mock.lookupAddress.return_value = ([answer_a], None, None)
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cache = {}
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servers = yield resolve_service(
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service_name, dns_client=dns_client_mock, cache=cache
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)
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dns_client_mock.lookupService.assert_called_once_with(service_name)
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dns_client_mock.lookupAddress.assert_called_once_with(host_name)
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self.assertEquals(len(servers), 1)
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self.assertEquals(servers, cache[service_name])
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self.assertEquals(servers[0].host, ip_address)
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@defer.inlineCallbacks
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def test_from_cache(self):
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dns_client_mock = Mock()
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dns_client_mock.lookupService.return_value = defer.fail(error.DNSServerError())
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service_name = "test_service.examle.com"
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cache = {
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service_name: [object()]
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}
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servers = yield resolve_service(
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service_name, dns_client=dns_client_mock, cache=cache
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)
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dns_client_mock.lookupService.assert_called_once_with(service_name)
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self.assertEquals(len(servers), 1)
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self.assertEquals(servers, cache[service_name])
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@defer.inlineCallbacks
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def test_empty_cache(self):
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dns_client_mock = Mock()
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dns_client_mock.lookupService.return_value = defer.fail(error.DNSServerError())
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service_name = "test_service.examle.com"
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cache = {}
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with self.assertRaises(error.DNSServerError):
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yield resolve_service(
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service_name, dns_client=dns_client_mock, cache=cache
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)
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@defer.inlineCallbacks
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def test_name_error(self):
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dns_client_mock = Mock()
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dns_client_mock.lookupService.return_value = defer.fail(error.DNSNameError())
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service_name = "test_service.examle.com"
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cache = {}
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servers = yield resolve_service(
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service_name, dns_client=dns_client_mock, cache=cache
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)
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self.assertEquals(len(servers), 0)
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self.assertEquals(len(cache), 0)
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