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

This commit is contained in:
Erik Johnston 2016-01-20 11:34:09 +00:00
parent af30140621
commit 191070123d
2 changed files with 186 additions and 30 deletions

View file

@ -17,7 +17,7 @@ from twisted.internet.endpoints import SSL4ClientEndpoint, TCP4ClientEndpoint
from twisted.internet import defer
from twisted.internet.error import ConnectError
from twisted.names import client, dns
from twisted.names.error import DNSNameError
from twisted.names.error import DNSNameError, DomainError
import collections
import logging
@ -27,6 +27,14 @@ import random
logger = logging.getLogger(__name__)
SERVER_CACHE = {}
_Server = collections.namedtuple(
"_Server", "priority weight host port"
)
def matrix_federation_endpoint(reactor, destination, ssl_context_factory=None,
timeout=None):
"""Construct an endpoint for the given matrix destination.
@ -73,10 +81,6 @@ class SRVClientEndpoint(object):
Implements twisted.internet.interfaces.IStreamClientEndpoint.
"""
_Server = collections.namedtuple(
"_Server", "priority weight host port"
)
def __init__(self, reactor, service, domain, protocol="tcp",
default_port=None, endpoint=TCP4ClientEndpoint,
endpoint_kw_args={}):
@ -101,32 +105,8 @@ class SRVClientEndpoint(object):
@defer.inlineCallbacks
def fetch_servers(self):
try:
answers, auth, add = yield client.lookupService(self.service_name)
except DNSNameError:
answers = []
if (len(answers) == 1
and answers[0].type == dns.SRV
and answers[0].payload
and answers[0].payload.target == dns.Name('.')):
raise ConnectError("Service %s unavailable", self.service_name)
self.servers = []
self.used_servers = []
for answer in answers:
if answer.type != dns.SRV or not answer.payload:
continue
payload = answer.payload
self.servers.append(self._Server(
host=str(payload.target),
port=int(payload.port),
priority=int(payload.priority),
weight=int(payload.weight)
))
self.servers.sort()
self.servers = yield resolve_service(self.service_name)
def pick_server(self):
if not self.servers:
@ -170,3 +150,64 @@ class SRVClientEndpoint(object):
)
connection = yield endpoint.connect(protocolFactory)
defer.returnValue(connection)
@defer.inlineCallbacks
def resolve_service(service_name, dns_client=client, cache=SERVER_CACHE):
servers = []
try:
try:
answers, _, _ = yield dns_client.lookupService(service_name)
except DNSNameError:
defer.returnValue([])
if (len(answers) == 1
and answers[0].type == dns.SRV
and answers[0].payload
and answers[0].payload.target == dns.Name('.')):
raise ConnectError("Service %s unavailable", service_name)
for answer in answers:
if answer.type != dns.SRV or not answer.payload:
continue
payload = answer.payload
host = str(payload.target)
try:
answers, _, _ = yield dns_client.lookupAddress(host)
except DNSNameError:
continue
ips = [
answer.payload.dottedQuad()
for answer in answers
if answer.type == dns.A and answer.payload
]
for ip in ips:
servers.append(_Server(
host=ip,
port=int(payload.port),
priority=int(payload.priority),
weight=int(payload.weight)
))
servers.sort()
cache[service_name] = list(servers)
except DomainError as e:
# We failed to resolve the name (other than a NameError)
# Try something in the cache, else rereaise
cache_entry = cache.get(service_name, None)
if cache_entry:
logger.warn(
"Failed to resolve %r, falling back to cache. %r",
service_name, e
)
servers = list(cache_entry)
else:
raise e
defer.returnValue(servers)

115
tests/test_dns.py Normal file
View file

@ -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)