diff --git a/synapse/http/federation/matrix_federation_agent.py b/synapse/http/federation/matrix_federation_agent.py
new file mode 100644
index 0000000000..384d8a37a2
--- /dev/null
+++ b/synapse/http/federation/matrix_federation_agent.py
@@ -0,0 +1,452 @@
+# -*- 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 json
+import logging
+import random
+import time
+
+import attr
+from netaddr import IPAddress
+from zope.interface import implementer
+
+from twisted.internet import defer
+from twisted.internet.endpoints import HostnameEndpoint, wrapClientTLS
+from twisted.internet.interfaces import IStreamClientEndpoint
+from twisted.web.client import URI, Agent, HTTPConnectionPool, RedirectAgent, readBody
+from twisted.web.http import stringToDatetime
+from twisted.web.http_headers import Headers
+from twisted.web.iweb import IAgent
+
+from synapse.http.federation.srv_resolver import SrvResolver, pick_server_from_list
+from synapse.util import Clock
+from synapse.util.caches.ttlcache import TTLCache
+from synapse.util.logcontext import make_deferred_yieldable
+from synapse.util.metrics import Measure
+
+# period to cache .well-known results for by default
+WELL_KNOWN_DEFAULT_CACHE_PERIOD = 24 * 3600
+
+# jitter to add to the .well-known default cache ttl
+WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER = 10 * 60
+
+# period to cache failure to fetch .well-known for
+WELL_KNOWN_INVALID_CACHE_PERIOD = 1 * 3600
+
+# cap for .well-known cache period
+WELL_KNOWN_MAX_CACHE_PERIOD = 48 * 3600
+
+logger = logging.getLogger(__name__)
+well_known_cache = TTLCache('well-known')
+
+
+@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.
+
+ _well_known_tls_policy (IPolicyForHTTPS|None):
+ TLS policy to use for fetching .well-known files. None to use a default
+ (browser-like) implementation.
+
+ srv_resolver (SrvResolver|None):
+ SRVResolver impl to use for looking up SRV records. None to use a default
+ implementation.
+ """
+
+ def __init__(
+ self, reactor, tls_client_options_factory,
+ _well_known_tls_policy=None,
+ _srv_resolver=None,
+ _well_known_cache=well_known_cache,
+ ):
+ self._reactor = reactor
+ self._clock = Clock(reactor)
+
+ self._tls_client_options_factory = tls_client_options_factory
+ if _srv_resolver is None:
+ _srv_resolver = SrvResolver()
+ self._srv_resolver = _srv_resolver
+
+ self._pool = HTTPConnectionPool(reactor)
+ self._pool.retryAutomatically = False
+ self._pool.maxPersistentPerHost = 5
+ self._pool.cachedConnectionTimeout = 2 * 60
+
+ agent_args = {}
+ if _well_known_tls_policy is not None:
+ # the param is called 'contextFactory', but actually passing a
+ # contextfactory is deprecated, and it expects an IPolicyForHTTPS.
+ agent_args['contextFactory'] = _well_known_tls_policy
+ _well_known_agent = RedirectAgent(
+ Agent(self._reactor, pool=self._pool, **agent_args),
+ )
+ self._well_known_agent = _well_known_agent
+
+ # our cache of .well-known lookup results, mapping from server name
+ # to delegated name. The values can be:
+ # `bytes`: a valid server-name
+ # `None`: there is no (valid) .well-known here
+ self._well_known_cache = _well_known_cache
+
+ @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, defaultPort=-1)
+ res = yield self._route_matrix_uri(parsed_uri)
+
+ # set up the TLS connection params
+ #
+ # 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(
+ res.tls_server_name.decode("ascii")
+ )
+
+ # make sure that the Host header is set correctly
+ if headers is None:
+ headers = Headers()
+ else:
+ headers = headers.copy()
+
+ if not headers.hasHeader(b'host'):
+ headers.addRawHeader(b'host', res.host_header)
+
+ class EndpointFactory(object):
+ @staticmethod
+ def endpointForURI(_uri):
+ ep = LoggingHostnameEndpoint(
+ self._reactor, res.target_host, res.target_port,
+ )
+ 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)
+
+ @defer.inlineCallbacks
+ def _route_matrix_uri(self, parsed_uri, lookup_well_known=True):
+ """Helper for `request`: determine the routing for a Matrix URI
+
+ Args:
+ parsed_uri (twisted.web.client.URI): uri to route. Note that it should be
+ parsed with URI.fromBytes(uri, defaultPort=-1) to set the `port` to -1
+ if there is no explicit port given.
+
+ lookup_well_known (bool): True if we should look up the .well-known file if
+ there is no SRV record.
+
+ Returns:
+ Deferred[_RoutingResult]
+ """
+ # check for an IP literal
+ try:
+ ip_address = IPAddress(parsed_uri.host.decode("ascii"))
+ except Exception:
+ # not an IP address
+ ip_address = None
+
+ if ip_address:
+ port = parsed_uri.port
+ if port == -1:
+ port = 8448
+ defer.returnValue(_RoutingResult(
+ host_header=parsed_uri.netloc,
+ tls_server_name=parsed_uri.host,
+ target_host=parsed_uri.host,
+ target_port=port,
+ ))
+
+ if parsed_uri.port != -1:
+ # there is an explicit port
+ defer.returnValue(_RoutingResult(
+ host_header=parsed_uri.netloc,
+ tls_server_name=parsed_uri.host,
+ target_host=parsed_uri.host,
+ target_port=parsed_uri.port,
+ ))
+
+ if lookup_well_known:
+ # try a .well-known lookup
+ well_known_server = yield self._get_well_known(parsed_uri.host)
+
+ if well_known_server:
+ # if we found a .well-known, start again, but don't do another
+ # .well-known lookup.
+
+ # parse the server name in the .well-known response into host/port.
+ # (This code is lifted from twisted.web.client.URI.fromBytes).
+ if b':' in well_known_server:
+ well_known_host, well_known_port = well_known_server.rsplit(b':', 1)
+ try:
+ well_known_port = int(well_known_port)
+ except ValueError:
+ # the part after the colon could not be parsed as an int
+ # - we assume it is an IPv6 literal with no port (the closing
+ # ']' stops it being parsed as an int)
+ well_known_host, well_known_port = well_known_server, -1
+ else:
+ well_known_host, well_known_port = well_known_server, -1
+
+ new_uri = URI(
+ scheme=parsed_uri.scheme,
+ netloc=well_known_server,
+ host=well_known_host,
+ port=well_known_port,
+ path=parsed_uri.path,
+ params=parsed_uri.params,
+ query=parsed_uri.query,
+ fragment=parsed_uri.fragment,
+ )
+
+ res = yield self._route_matrix_uri(new_uri, lookup_well_known=False)
+ defer.returnValue(res)
+
+ # try a SRV lookup
+ service_name = b"_matrix._tcp.%s" % (parsed_uri.host,)
+ server_list = yield self._srv_resolver.resolve_service(service_name)
+
+ if not server_list:
+ target_host = parsed_uri.host
+ port = 8448
+ logger.debug(
+ "No SRV record for %s, using %s:%i",
+ parsed_uri.host.decode("ascii"), target_host.decode("ascii"), port,
+ )
+ else:
+ target_host, port = pick_server_from_list(server_list)
+ logger.debug(
+ "Picked %s:%i from SRV records for %s",
+ target_host.decode("ascii"), port, parsed_uri.host.decode("ascii"),
+ )
+
+ defer.returnValue(_RoutingResult(
+ host_header=parsed_uri.netloc,
+ tls_server_name=parsed_uri.host,
+ target_host=target_host,
+ target_port=port,
+ ))
+
+ @defer.inlineCallbacks
+ def _get_well_known(self, server_name):
+ """Attempt to fetch and parse a .well-known file for the given server
+
+ Args:
+ server_name (bytes): name of the server, from the requested url
+
+ Returns:
+ Deferred[bytes|None]: either the new server name, from the .well-known, or
+ None if there was no .well-known file.
+ """
+ try:
+ result = self._well_known_cache[server_name]
+ except KeyError:
+ # TODO: should we linearise so that we don't end up doing two .well-known
+ # requests for the same server in parallel?
+ with Measure(self._clock, "get_well_known"):
+ result, cache_period = yield self._do_get_well_known(server_name)
+
+ if cache_period > 0:
+ self._well_known_cache.set(server_name, result, cache_period)
+
+ defer.returnValue(result)
+
+ @defer.inlineCallbacks
+ def _do_get_well_known(self, server_name):
+ """Actually fetch and parse a .well-known, without checking the cache
+
+ Args:
+ server_name (bytes): name of the server, from the requested url
+
+ Returns:
+ Deferred[Tuple[bytes|None|object],int]:
+ result, cache period, where result is one of:
+ - the new server name from the .well-known (as a `bytes`)
+ - None if there was no .well-known file.
+ - INVALID_WELL_KNOWN if the .well-known was invalid
+ """
+ uri = b"https://%s/.well-known/matrix/server" % (server_name, )
+ uri_str = uri.decode("ascii")
+ logger.info("Fetching %s", uri_str)
+ try:
+ response = yield make_deferred_yieldable(
+ self._well_known_agent.request(b"GET", uri),
+ )
+ body = yield make_deferred_yieldable(readBody(response))
+ if response.code != 200:
+ raise Exception("Non-200 response %s" % (response.code, ))
+
+ parsed_body = json.loads(body.decode('utf-8'))
+ logger.info("Response from .well-known: %s", parsed_body)
+ if not isinstance(parsed_body, dict):
+ raise Exception("not a dict")
+ if "m.server" not in parsed_body:
+ raise Exception("Missing key 'm.server'")
+ except Exception as e:
+ logger.info("Error fetching %s: %s", uri_str, e)
+
+ # add some randomness to the TTL to avoid a stampeding herd every hour
+ # after startup
+ cache_period = WELL_KNOWN_INVALID_CACHE_PERIOD
+ cache_period += random.uniform(0, WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER)
+ defer.returnValue((None, cache_period))
+
+ result = parsed_body["m.server"].encode("ascii")
+
+ cache_period = _cache_period_from_headers(
+ response.headers,
+ time_now=self._reactor.seconds,
+ )
+ if cache_period is None:
+ cache_period = WELL_KNOWN_DEFAULT_CACHE_PERIOD
+ # add some randomness to the TTL to avoid a stampeding herd every 24 hours
+ # after startup
+ cache_period += random.uniform(0, WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER)
+ else:
+ cache_period = min(cache_period, WELL_KNOWN_MAX_CACHE_PERIOD)
+
+ defer.returnValue((result, cache_period))
+
+
+@implementer(IStreamClientEndpoint)
+class LoggingHostnameEndpoint(object):
+ """A wrapper for HostnameEndpint which logs when it connects"""
+ def __init__(self, reactor, host, port, *args, **kwargs):
+ self.host = host
+ self.port = port
+ self.ep = HostnameEndpoint(reactor, host, port, *args, **kwargs)
+
+ def connect(self, protocol_factory):
+ logger.info("Connecting to %s:%i", self.host.decode("ascii"), self.port)
+ return self.ep.connect(protocol_factory)
+
+
+def _cache_period_from_headers(headers, time_now=time.time):
+ cache_controls = _parse_cache_control(headers)
+
+ if b'no-store' in cache_controls:
+ return 0
+
+ if b'max-age' in cache_controls:
+ try:
+ max_age = int(cache_controls[b'max-age'])
+ return max_age
+ except ValueError:
+ pass
+
+ expires = headers.getRawHeaders(b'expires')
+ if expires is not None:
+ try:
+ expires_date = stringToDatetime(expires[-1])
+ return expires_date - time_now()
+ except ValueError:
+ # RFC7234 says 'A cache recipient MUST interpret invalid date formats,
+ # especially the value "0", as representing a time in the past (i.e.,
+ # "already expired").
+ return 0
+
+ return None
+
+
+def _parse_cache_control(headers):
+ cache_controls = {}
+ for hdr in headers.getRawHeaders(b'cache-control', []):
+ for directive in hdr.split(b','):
+ splits = [x.strip() for x in directive.split(b'=', 1)]
+ k = splits[0].lower()
+ v = splits[1] if len(splits) > 1 else None
+ cache_controls[k] = v
+ return cache_controls
+
+
+@attr.s
+class _RoutingResult(object):
+ """The result returned by `_route_matrix_uri`.
+
+ Contains the parameters needed to direct a federation connection to a particular
+ server.
+
+ Where a SRV record points to several servers, this object contains a single server
+ chosen from the list.
+ """
+
+ host_header = attr.ib()
+ """
+ The value we should assign to the Host header (host:port from the matrix
+ URI, or .well-known).
+
+ :type: bytes
+ """
+
+ tls_server_name = attr.ib()
+ """
+ The server name we should set in the SNI (typically host, without port, from the
+ matrix URI or .well-known)
+
+ :type: bytes
+ """
+
+ target_host = attr.ib()
+ """
+ The hostname (or IP literal) we should route the TCP connection to (the target of the
+ SRV record, or the hostname from the URL/.well-known)
+
+ :type: bytes
+ """
+
+ target_port = attr.ib()
+ """
+ The port we should route the TCP connection to (the target of the SRV record, or
+ the port from the URL/.well-known, or 8448)
+
+ :type: int
+ """
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