Fix idna and ipv6 literal handling in MatrixFederationAgent (#4487)

Turns out that the library does a better job of parsing URIs than our
reinvented wheel. Who knew.

There are two things going on here. The first is that, unlike
parse_server_name, URI.fromBytes will strip off square brackets from IPv6
literals, which means that it is valid input to ClientTLSOptionsFactory and
HostnameEndpoint.

The second is that we stay in `bytes` throughout (except for the argument to
ClientTLSOptionsFactory), which avoids the weirdness of (sometimes) ending up
with idna-encoded values being held in `unicode` variables. TBH it probably
would have been ok but it made the tests fragile.

3 files changed, 193 insertions, 12 deletions

diff --git a/changelog.d/4487.misc b/changelog.d/4487.misc
new file mode 100644
index 0000000000..79de8eb3ad
--- /dev/null
+++ b/changelog.d/4487.misc
@@ -0,0 +1 @@
+Fix idna and ipv6 literal handling in MatrixFederationAgent
diff --git a/synapse/http/federation/matrix_federation_agent.py b/synapse/http/federation/matrix_federation_agent.py
index 1788e9a34a..9526f39cca 100644
--- a/synapse/http/federation/matrix_federation_agent.py
+++ b/synapse/http/federation/matrix_federation_agent.py
@@ -22,7 +22,6 @@ 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
 from synapse.http.federation.srv_resolver import SrvResolver, pick_server_from_list
 from synapse.util.logcontext import make_deferred_yieldable
 
@@ -87,9 +86,7 @@ class MatrixFederationAgent(object):
                 from being sent).
         """
 
-        parsed_uri = URI.fromBytes(uri)
-        server_name_bytes = parsed_uri.netloc
-        host, port = parse_server_name(server_name_bytes.decode("ascii"))
+        parsed_uri = URI.fromBytes(uri, defaultPort=-1)
 
         # 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
@@ -97,16 +94,20 @@ class MatrixFederationAgent(object):
         if self._tls_client_options_factory is None:
             tls_options = None
         else:
-            tls_options = self._tls_client_options_factory.get_options(host)
+            tls_options = self._tls_client_options_factory.get_options(
+                parsed_uri.host.decode("ascii")
+            )
 
-        if port is not None:
-            target = (host, port)
+        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" % (server_name_bytes, )
+            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, 8448)
-                logger.debug("No SRV record for %s, using %s", host, target)
+                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)
 
@@ -117,7 +118,7 @@ class MatrixFederationAgent(object):
             headers = headers.copy()
 
         if not headers.hasHeader(b'host'):
-            headers.addRawHeader(b'host', server_name_bytes)
+            headers.addRawHeader(b'host', parsed_uri.netloc)
 
         class EndpointFactory(object):
             @staticmethod
diff --git a/tests/http/federation/test_matrix_federation_agent.py b/tests/http/federation/test_matrix_federation_agent.py
index 261afb5f41..f144092a51 100644
--- a/tests/http/federation/test_matrix_federation_agent.py
+++ b/tests/http/federation/test_matrix_federation_agent.py
@@ -209,6 +209,95 @@ class MatrixFederationAgentTests(TestCase):
         self.reactor.pump((0.1,))
         self.successResultOf(test_d)
 
+    def test_get_ipv6_address(self):
+        """
+        Test the behaviour when the server name contains an explicit IPv6 address
+        (with no port)
+        """
+
+        # the SRV lookup will return an empty list (XXX: why do we even do an SRV lookup?)
+        self.mock_resolver.resolve_service.side_effect = lambda _: []
+
+        # then there will be a getaddrinfo on the IP
+        self.reactor.lookups["::1"] = "::1"
+
+        test_d = self._make_get_request(b"matrix://[::1]/foo/bar")
+
+        # Nothing happened yet
+        self.assertNoResult(test_d)
+
+        self.mock_resolver.resolve_service.assert_called_once_with(
+            b"_matrix._tcp.::1",
+        )
+
+        # Make sure treq is trying to connect
+        clients = self.reactor.tcpClients
+        self.assertEqual(len(clients), 1)
+        (host, port, client_factory, _timeout, _bindAddress) = clients[0]
+        self.assertEqual(host, '::1')
+        self.assertEqual(port, 8448)
+
+        # make a test server, and wire up the client
+        http_server = self._make_connection(
+            client_factory,
+            expected_sni=None,
+        )
+
+        self.assertEqual(len(http_server.requests), 1)
+        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]'],
+        )
+
+        # finish the request
+        request.finish()
+        self.reactor.pump((0.1,))
+        self.successResultOf(test_d)
+
+    def test_get_ipv6_address_with_port(self):
+        """
+        Test the behaviour when the server name contains an explicit IPv6 address
+        (with explicit port)
+        """
+
+        # there will be a getaddrinfo on the IP
+        self.reactor.lookups["::1"] = "::1"
+
+        test_d = self._make_get_request(b"matrix://[::1]:80/foo/bar")
+
+        # Nothing happened yet
+        self.assertNoResult(test_d)
+
+        # Make sure treq is trying to connect
+        clients = self.reactor.tcpClients
+        self.assertEqual(len(clients), 1)
+        (host, port, client_factory, _timeout, _bindAddress) = clients[0]
+        self.assertEqual(host, '::1')
+        self.assertEqual(port, 80)
+
+        # make a test server, and wire up the client
+        http_server = self._make_connection(
+            client_factory,
+            expected_sni=None,
+        )
+
+        self.assertEqual(len(http_server.requests), 1)
+        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]:80'],
+        )
+
+        # finish the request
+        request.finish()
+        self.reactor.pump((0.1,))
+        self.successResultOf(test_d)
+
     def test_get_hostname_no_srv(self):
         """
         Test the behaviour when the server name has no port, and no SRV record
@@ -258,7 +347,7 @@ class MatrixFederationAgentTests(TestCase):
         Test the behaviour when there is a single SRV record
         """
         self.mock_resolver.resolve_service.side_effect = lambda _: [
-            Server(host="srvtarget", port=8443)
+            Server(host=b"srvtarget", port=8443)
         ]
         self.reactor.lookups["srvtarget"] = "1.2.3.4"
 
@@ -298,6 +387,96 @@ class MatrixFederationAgentTests(TestCase):
         self.reactor.pump((0.1,))
         self.successResultOf(test_d)
 
+    def test_idna_servername(self):
+        """test the behaviour when the server name has idna chars in"""
+
+        self.mock_resolver.resolve_service.side_effect = lambda _: []
+
+        # hostnameendpoint does the lookup on the unicode value (getaddrinfo encodes
+        # it back to idna)
+        self.reactor.lookups[u"bücher.com"] = "1.2.3.4"
+
+        # this is idna for bücher.com
+        test_d = self._make_get_request(b"matrix://xn--bcher-kva.com/foo/bar")
+
+        # Nothing happened yet
+        self.assertNoResult(test_d)
+
+        self.mock_resolver.resolve_service.assert_called_once_with(
+            b"_matrix._tcp.xn--bcher-kva.com",
+        )
+
+        # Make sure treq is trying to connect
+        clients = self.reactor.tcpClients
+        self.assertEqual(len(clients), 1)
+        (host, port, client_factory, _timeout, _bindAddress) = clients[0]
+        self.assertEqual(host, '1.2.3.4')
+        self.assertEqual(port, 8448)
+
+        # make a test server, and wire up the client
+        http_server = self._make_connection(
+            client_factory,
+            expected_sni=b'xn--bcher-kva.com',
+        )
+
+        self.assertEqual(len(http_server.requests), 1)
+        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'xn--bcher-kva.com'],
+        )
+
+        # finish the request
+        request.finish()
+        self.reactor.pump((0.1,))
+        self.successResultOf(test_d)
+
+    def test_idna_srv_target(self):
+        """test the behaviour when the target of a SRV record has idna chars"""
+
+        self.mock_resolver.resolve_service.side_effect = lambda _: [
+            Server(host=b"xn--trget-3qa.com", port=8443)  # târget.com
+        ]
+        self.reactor.lookups[u"târget.com"] = "1.2.3.4"
+
+        test_d = self._make_get_request(b"matrix://xn--bcher-kva.com/foo/bar")
+
+        # Nothing happened yet
+        self.assertNoResult(test_d)
+
+        self.mock_resolver.resolve_service.assert_called_once_with(
+            b"_matrix._tcp.xn--bcher-kva.com",
+        )
+
+        # Make sure treq is trying to connect
+        clients = self.reactor.tcpClients
+        self.assertEqual(len(clients), 1)
+        (host, port, client_factory, _timeout, _bindAddress) = clients[0]
+        self.assertEqual(host, '1.2.3.4')
+        self.assertEqual(port, 8443)
+
+        # make a test server, and wire up the client
+        http_server = self._make_connection(
+            client_factory,
+            expected_sni=b'xn--bcher-kva.com',
+        )
+
+        self.assertEqual(len(http_server.requests), 1)
+        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'xn--bcher-kva.com'],
+        )
+
+        # finish the request
+        request.finish()
+        self.reactor.pump((0.1,))
+        self.successResultOf(test_d)
+
 
 def _check_logcontext(context):
     current = LoggingContext.current_context()