Fix Host header sent by MatrixFederationAgent (#4468)

Move the Host header logic down here so that (a) it is used if we reuse the
agent elsewhere, and (b) we can mess about with it with .well-known.

changelog.d/4468.misc

+Move SRV logic into the Agent layer

synapse/http/federation/matrix_federation_agent.py

@@ -19,6 +19,7 @@ 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.http_headers import Headers
 from twisted.web.iweb import IAgent
 
 from synapse.http.endpoint import parse_server_name
@@ -109,6 +110,15 @@ class MatrixFederationAgent(object):
             else:
                 target = pick_server_from_list(server_list)
 
+        # 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', server_name_bytes)
+
         class EndpointFactory(object):
             @staticmethod
             def endpointForURI(_uri):

synapse/http/matrixfederationclient.py

@@ -255,7 +255,6 @@ class MatrixFederationHttpClient(object):
 
         headers_dict = {
             b"User-Agent": [self.version_string_bytes],
-            b"Host": [destination_bytes],
         }
 
         with limiter:

tests/http/federation/test_matrix_federation_agent.py

@@ -131,6 +131,10 @@ class MatrixFederationAgentTests(TestCase):
         request = http_server.requests[0]
         self.assertEqual(request.method, b'GET')
         self.assertEqual(request.path, b'/foo/bar')
+        self.assertEqual(
+            request.requestHeaders.getRawHeaders(b'host'),
+            [b'testserv:8448']
+        )
         content = request.content.read()
         self.assertEqual(content, b'')
 
@@ -195,6 +199,10 @@ class MatrixFederationAgentTests(TestCase):
         request = http_server.requests[0]
         self.assertEqual(request.method, b'GET')
         self.assertEqual(request.path, b'/foo/bar')
+        self.assertEqual(
+            request.requestHeaders.getRawHeaders(b'host'),
+            [b'1.2.3.4'],
+        )
 
         # finish the request
         request.finish()
@@ -235,6 +243,10 @@ class MatrixFederationAgentTests(TestCase):
         request = http_server.requests[0]
         self.assertEqual(request.method, b'GET')
         self.assertEqual(request.path, b'/foo/bar')
+        self.assertEqual(
+            request.requestHeaders.getRawHeaders(b'host'),
+            [b'testserv'],
+        )
 
         # finish the request
         request.finish()
@@ -276,6 +288,10 @@ class MatrixFederationAgentTests(TestCase):
         request = http_server.requests[0]
         self.assertEqual(request.method, b'GET')
         self.assertEqual(request.path, b'/foo/bar')
+        self.assertEqual(
+            request.requestHeaders.getRawHeaders(b'host'),
+            [b'testserv'],
+        )
 
         # finish the request
         request.finish()

tests/http/test_fedclient.py

@@ -49,7 +49,6 @@ class FederationClientTests(HomeserverTestCase):
         return hs
 
     def prepare(self, reactor, clock, homeserver):
-
         self.cl = MatrixFederationHttpClient(self.hs)
         self.reactor.lookups["testserv"] = "1.2.3.4"
 
@@ -95,6 +94,7 @@ class FederationClientTests(HomeserverTestCase):
 
         # that should have made it send the request to the transport
         self.assertRegex(transport.value(), b"^GET /foo/bar")
+        self.assertRegex(transport.value(), b"Host: testserv:8008")
 
         # Deferred is still without a result
         self.assertNoResult(test_d)