diff options
Diffstat (limited to 'synapse/http/federation')
| -rw-r--r-- | synapse/http/federation/__init__.py | 14 | ||||
| -rw-r--r-- | synapse/http/federation/srv_resolver.py | 124 |
2 files changed, 138 insertions, 0 deletions
diff --git a/synapse/http/federation/__init__.py b/synapse/http/federation/__init__.py new file mode 100644 index 0000000000..1453d04571 --- /dev/null +++ b/synapse/http/federation/__init__.py @@ -0,0 +1,14 @@ +# -*- coding: utf-8 -*- +# Copyright 2019 New Vector 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. diff --git a/synapse/http/federation/srv_resolver.py b/synapse/http/federation/srv_resolver.py new file mode 100644 index 0000000000..c49b82c394 --- /dev/null +++ b/synapse/http/federation/srv_resolver.py @@ -0,0 +1,124 @@ +# -*- coding: utf-8 -*- +# Copyright 2014-2016 OpenMarket Ltd +# Copyright 2019 New Vector 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. + +import logging +import time + +import attr + +from twisted.internet import defer +from twisted.internet.error import ConnectError +from twisted.names import client, dns +from twisted.names.error import DNSNameError, DomainError + +from synapse.util.logcontext import make_deferred_yieldable + +logger = logging.getLogger(__name__) + +SERVER_CACHE = {} + + +@attr.s +class Server(object): + """ + Our record of an individual server which can be tried to reach a destination. + + Attributes: + host (bytes): target hostname + port (int): + priority (int): + weight (int): + expires (int): when the cache should expire this record - in *seconds* since + the epoch + """ + host = attr.ib() + port = attr.ib() + priority = attr.ib(default=0) + weight = attr.ib(default=0) + expires = attr.ib(default=0) + + +@defer.inlineCallbacks +def resolve_service(service_name, dns_client=client, cache=SERVER_CACHE, clock=time): + """Look up a SRV record, with caching + + The default resolver in twisted.names doesn't do any caching (it has a CacheResolver, + but the cache never gets populated), so we add our own caching layer here. + + Args: + service_name (unicode|bytes): record to look up + dns_client (twisted.internet.interfaces.IResolver): twisted resolver impl + cache (dict): cache object + clock (object): clock implementation. must provide a time() method. + + Returns: + Deferred[list[Server]]: a list of the SRV records, or an empty list if none found + """ + # TODO: the dns client handles both unicode names (encoding via idna) and pre-encoded + # byteses; however they will obviously end up as separate entries in the cache. We + # should pick one form and stick with it. + cache_entry = cache.get(service_name, None) + if cache_entry: + if all(s.expires > int(clock.time()) for s in cache_entry): + servers = list(cache_entry) + defer.returnValue(servers) + + try: + answers, _, _ = yield make_deferred_yieldable( + dns_client.lookupService(service_name), + ) + except DNSNameError: + # TODO: cache this. We can get the SOA out of the exception, and use + # the negative-TTL value. + defer.returnValue([]) + 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 + ) + defer.returnValue(list(cache_entry)) + else: + raise e + + if (len(answers) == 1 + and answers[0].type == dns.SRV + and answers[0].payload + and answers[0].payload.target == dns.Name(b'.')): + raise ConnectError("Service %s unavailable" % service_name) + + servers = [] + + for answer in answers: + if answer.type != dns.SRV or not answer.payload: + continue + + payload = answer.payload + + servers.append(Server( + host=payload.target.name, + port=payload.port, + priority=payload.priority, + weight=payload.weight, + expires=int(clock.time()) + answer.ttl, + )) + + servers.sort() # FIXME: get rid of this (it's broken by the attrs change) + cache[service_name] = list(servers) + defer.returnValue(servers) |