diff --git a/synapse/http/federation/matrix_federation_agent.py b/synapse/http/federation/matrix_federation_agent.py
new file mode 100644
index 0000000000..32bfd68ed1
--- /dev/null
+++ b/synapse/http/federation/matrix_federation_agent.py
@@ -0,0 +1,114 @@
+# -*- 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.
+import logging
+
+from zope.interface import implementer
+
+from twisted.internet import defer
+from twisted.internet.endpoints import HostnameEndpoint, wrapClientTLS
+from twisted.web.client import URI, Agent, HTTPConnectionPool
+from twisted.web.iweb import IAgent
+
+from synapse.http.endpoint import parse_server_name
+from synapse.http.federation.srv_resolver import pick_server_from_list, resolve_service
+from synapse.util.logcontext import make_deferred_yieldable
+
+logger = logging.getLogger(__name__)
+
+
+@implementer(IAgent)
+class MatrixFederationAgent(object):
+ """An Agent-like thing which provides a `request` method which will look up a matrix
+ server and send an HTTP request to it.
+
+ Doesn't implement any retries. (Those are done in MatrixFederationHttpClient.)
+
+ Args:
+ reactor (IReactor): twisted reactor to use for underlying requests
+ tls_client_options_factory (ClientTLSOptionsFactory|None):
+ factory to use for fetching client tls options, or none to disable TLS.
+ """
+
+ def __init__(self, reactor, tls_client_options_factory):
+ self._reactor = reactor
+ self._tls_client_options_factory = tls_client_options_factory
+
+ self._pool = HTTPConnectionPool(reactor)
+ self._pool.retryAutomatically = False
+ self._pool.maxPersistentPerHost = 5
+ self._pool.cachedConnectionTimeout = 2 * 60
+
+ @defer.inlineCallbacks
+ def request(self, method, uri, headers=None, bodyProducer=None):
+ """
+ Args:
+ method (bytes): HTTP method: GET/POST/etc
+
+ uri (bytes): Absolute URI to be retrieved
+
+ headers (twisted.web.http_headers.Headers|None):
+ HTTP headers to send with the request, or None to
+ send no extra headers.
+
+ bodyProducer (twisted.web.iweb.IBodyProducer|None):
+ An object which can generate bytes to make up the
+ body of this request (for example, the properly encoded contents of
+ a file for a file upload). Or None if the request is to have
+ no body.
+
+ Returns:
+ Deferred[twisted.web.iweb.IResponse]:
+ fires when the header of the response has been received (regardless of the
+ response status code). Fails if there is any problem which prevents that
+ response from being received (including problems that prevent the request
+ from being sent).
+ """
+
+ parsed_uri = URI.fromBytes(uri)
+ server_name_bytes = parsed_uri.netloc
+ host, port = parse_server_name(server_name_bytes.decode("ascii"))
+
+ # XXX disabling TLS is really only supported here for the benefit of the
+ # unit tests. We should make the UTs cope with TLS rather than having to make
+ # the code support the unit tests.
+ if self._tls_client_options_factory is None:
+ tls_options = None
+ else:
+ tls_options = self._tls_client_options_factory.get_options(host)
+
+ if port is not None:
+ target = (host, port)
+ else:
+ server_list = yield resolve_service(server_name_bytes)
+ if not server_list:
+ target = (host, 8448)
+ logger.debug("No SRV record for %s, using %s", host, target)
+ else:
+ target = pick_server_from_list(server_list)
+
+ class EndpointFactory(object):
+ @staticmethod
+ def endpointForURI(_uri):
+ logger.info("Connecting to %s:%s", target[0], target[1])
+ ep = HostnameEndpoint(self._reactor, host=target[0], port=target[1])
+ if tls_options is not None:
+ ep = wrapClientTLS(tls_options, ep)
+ return ep
+
+ agent = Agent.usingEndpointFactory(self._reactor, EndpointFactory(), self._pool)
+ res = yield make_deferred_yieldable(
+ agent.request(method, uri, headers, bodyProducer)
+ )
+ defer.returnValue(res)
diff --git a/synapse/http/federation/srv_resolver.py b/synapse/http/federation/srv_resolver.py
index c49b82c394..ded0b32832 100644
--- a/synapse/http/federation/srv_resolver.py
+++ b/synapse/http/federation/srv_resolver.py
@@ -15,6 +15,7 @@
# limitations under the License.
import logging
+import random
import time
import attr
@@ -51,6 +52,38 @@ class Server(object):
expires = attr.ib(default=0)
+def pick_server_from_list(server_list):
+ """Randomly choose a server from the server list
+
+ Args:
+ server_list (list[Server]): list of candidate servers
+
+ Returns:
+ Tuple[bytes, int]: (host, port) pair for the chosen server
+ """
+ if not server_list:
+ raise RuntimeError("pick_server_from_list called with empty list")
+
+ # TODO: currently we only use the lowest-priority servers. We should maintain a
+ # cache of servers known to be "down" and filter them out
+
+ min_priority = min(s.priority for s in server_list)
+ eligible_servers = list(s for s in server_list if s.priority == min_priority)
+ total_weight = sum(s.weight for s in eligible_servers)
+ target_weight = random.randint(0, total_weight)
+
+ for s in eligible_servers:
+ target_weight -= s.weight
+
+ if target_weight <= 0:
+ return s.host, s.port
+
+ # this should be impossible.
+ raise RuntimeError(
+ "pick_server_from_list got to end of eligible server list.",
+ )
+
+
@defer.inlineCallbacks
def resolve_service(service_name, dns_client=client, cache=SERVER_CACHE, clock=time):
"""Look up a SRV record, with caching
|
