From 51958df766667a75236764c9df57cfd60d57bd5e Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <richard@matrix.org>
Date: Sun, 27 Jan 2019 23:24:17 +0000
Subject: [PATCH] MatrixFederationAgent: factor out routing logic

This is going to get too big and unmanageable.
---
 .../federation/matrix_federation_agent.py     | 80 ++++++++++++++-----
 1 file changed, 62 insertions(+), 18 deletions(-)

diff --git a/synapse/http/federation/matrix_federation_agent.py b/synapse/http/federation/matrix_federation_agent.py
index 9526f39cc..2a8bceed9 100644
--- a/synapse/http/federation/matrix_federation_agent.py
+++ b/synapse/http/federation/matrix_federation_agent.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 import logging
 
+import attr
 from zope.interface import implementer
 
 from twisted.internet import defer
@@ -85,9 +86,11 @@ class MatrixFederationAgent(object):
                 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.
@@ -95,22 +98,9 @@ class MatrixFederationAgent(object):
             tls_options = None
         else:
             tls_options = self._tls_client_options_factory.get_options(
-                parsed_uri.host.decode("ascii")
+                res.tls_server_name.decode("ascii")
             )
 
-        if parsed_uri.port != -1:
-            # there was an explicit port in the URI
-            target = parsed_uri.host, parsed_uri.port
-        else:
-            service_name = b"_matrix._tcp.%s" % (parsed_uri.host, )
-            server_list = yield self._srv_resolver.resolve_service(service_name)
-            if not server_list:
-                target = (parsed_uri.host, 8448)
-                logger.debug(
-                    "No SRV record for %s, using %s", service_name, target)
-            else:
-                target = pick_server_from_list(server_list)
-
         # make sure that the Host header is set correctly
         if headers is None:
             headers = Headers()
@@ -118,13 +108,13 @@ class MatrixFederationAgent(object):
             headers = headers.copy()
 
         if not headers.hasHeader(b'host'):
-            headers.addRawHeader(b'host', parsed_uri.netloc)
+            headers.addRawHeader(b'host', res.host_header)
 
         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])
+                logger.info("Connecting to %s:%s", res.target_host, res.target_port)
+                ep = HostnameEndpoint(self._reactor, res.target_host, res.target_port)
                 if tls_options is not None:
                     ep = wrapClientTLS(tls_options, ep)
                 return ep
@@ -134,3 +124,57 @@ class MatrixFederationAgent(object):
             agent.request(method, uri, headers, bodyProducer)
         )
         defer.returnValue(res)
+
+    @defer.inlineCallbacks
+    def _route_matrix_uri(self, parsed_uri):
+        """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.
+
+        Returns:
+            Deferred[_RoutingResult]
+        """
+        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,
+            ))
+
+        # 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,
+        ))
+
+
+@attr.s
+class _RoutingResult(object):
+    host_header = attr.ib()
+    tls_server_name = attr.ib()
+    target_host = attr.ib()
+    target_port = attr.ib()