Support for routing outbound HTTP requests via a proxy (#6239)

The `http_proxy` and `HTTPS_PROXY` env vars can be set to a `host[:port]` value which should point to a proxy.

The address of the proxy should be excluded from IP blacklists such as the `url_preview_ip_range_blacklist`.

The proxy will then be used for
 * push
 * url previews
 * phone-home stats
 * recaptcha validation
 * CAS auth validation

It will *not* be used for:
 * Application Services
 * Identity servers
 * Outbound federation
 * In worker configurations, connections from workers to masters

Fixes #4198.

3 files changed, 359 insertions, 3 deletions

diff --git a/tests/http/__init__.py b/tests/http/__init__.py
index 2d5dba6464..2096ba3c91 100644
--- a/tests/http/__init__.py
+++ b/tests/http/__init__.py
@@ -20,6 +20,23 @@ from zope.interface import implementer
 from OpenSSL import SSL
 from OpenSSL.SSL import Connection
 from twisted.internet.interfaces import IOpenSSLServerConnectionCreator
+from twisted.internet.ssl import Certificate, trustRootFromCertificates
+from twisted.web.client import BrowserLikePolicyForHTTPS  # noqa: F401
+from twisted.web.iweb import IPolicyForHTTPS  # noqa: F401
+
+
+def get_test_https_policy():
+    """Get a test IPolicyForHTTPS which trusts the test CA cert
+
+    Returns:
+        IPolicyForHTTPS
+    """
+    ca_file = get_test_ca_cert_file()
+    with open(ca_file) as stream:
+        content = stream.read()
+    cert = Certificate.loadPEM(content)
+    trust_root = trustRootFromCertificates([cert])
+    return BrowserLikePolicyForHTTPS(trustRoot=trust_root)
 
 
 def get_test_ca_cert_file():
diff --git a/tests/http/federation/test_matrix_federation_agent.py b/tests/http/federation/test_matrix_federation_agent.py
index 71d7025264..cfcd98ff7d 100644
--- a/tests/http/federation/test_matrix_federation_agent.py
+++ b/tests/http/federation/test_matrix_federation_agent.py
@@ -124,19 +124,24 @@ class MatrixFederationAgentTests(unittest.TestCase):
             FakeTransport(client_protocol, self.reactor, server_tls_protocol)
         )
 
+        # grab a hold of the TLS connection, in case it gets torn down
+        server_tls_connection = server_tls_protocol._tlsConnection
+
+        # fish the test server back out of the server-side TLS protocol.
+        http_protocol = server_tls_protocol.wrappedProtocol
+
         # give the reactor a pump to get the TLS juices flowing.
         self.reactor.pump((0.1,))
 
         # check the SNI
-        server_name = server_tls_protocol._tlsConnection.get_servername()
+        server_name = server_tls_connection.get_servername()
         self.assertEqual(
             server_name,
             expected_sni,
             "Expected SNI %s but got %s" % (expected_sni, server_name),
         )
 
-        # fish the test server back out of the server-side TLS protocol.
-        return server_tls_protocol.wrappedProtocol
+        return http_protocol
 
     @defer.inlineCallbacks
     def _make_get_request(self, uri):
diff --git a/tests/http/test_proxyagent.py b/tests/http/test_proxyagent.py
new file mode 100644
index 0000000000..22abf76515
--- /dev/null
+++ b/tests/http/test_proxyagent.py
@@ -0,0 +1,334 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# 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
+
+import treq
+
+from twisted.internet import interfaces  # noqa: F401
+from twisted.internet.protocol import Factory
+from twisted.protocols.tls import TLSMemoryBIOFactory
+from twisted.web.http import HTTPChannel
+
+from synapse.http.proxyagent import ProxyAgent
+
+from tests.http import TestServerTLSConnectionFactory, get_test_https_policy
+from tests.server import FakeTransport, ThreadedMemoryReactorClock
+from tests.unittest import TestCase
+
+logger = logging.getLogger(__name__)
+
+HTTPFactory = Factory.forProtocol(HTTPChannel)
+
+
+class MatrixFederationAgentTests(TestCase):
+    def setUp(self):
+        self.reactor = ThreadedMemoryReactorClock()
+
+    def _make_connection(
+        self, client_factory, server_factory, ssl=False, expected_sni=None
+    ):
+        """Builds a test server, and completes the outgoing client connection
+
+        Args:
+            client_factory (interfaces.IProtocolFactory): the the factory that the
+                application is trying to use to make the outbound connection. We will
+                invoke it to build the client Protocol
+
+            server_factory (interfaces.IProtocolFactory): a factory to build the
+                server-side protocol
+
+            ssl (bool): If true, we will expect an ssl connection and wrap
+                server_factory with a TLSMemoryBIOFactory
+
+            expected_sni (bytes|None): the expected SNI value
+
+        Returns:
+            IProtocol: the server Protocol returned by server_factory
+        """
+        if ssl:
+            server_factory = _wrap_server_factory_for_tls(server_factory)
+
+        server_protocol = server_factory.buildProtocol(None)
+
+        # now, tell the client protocol factory to build the client protocol,
+        # and wire the output of said protocol up to the server via
+        # a FakeTransport.
+        #
+        # Normally this would be done by the TCP socket code in Twisted, but we are
+        # stubbing that out here.
+        client_protocol = client_factory.buildProtocol(None)
+        client_protocol.makeConnection(
+            FakeTransport(server_protocol, self.reactor, client_protocol)
+        )
+
+        # tell the server protocol to send its stuff back to the client, too
+        server_protocol.makeConnection(
+            FakeTransport(client_protocol, self.reactor, server_protocol)
+        )
+
+        if ssl:
+            http_protocol = server_protocol.wrappedProtocol
+            tls_connection = server_protocol._tlsConnection
+        else:
+            http_protocol = server_protocol
+            tls_connection = None
+
+        # give the reactor a pump to get the TLS juices flowing (if needed)
+        self.reactor.advance(0)
+
+        if expected_sni is not None:
+            server_name = tls_connection.get_servername()
+            self.assertEqual(
+                server_name,
+                expected_sni,
+                "Expected SNI %s but got %s" % (expected_sni, server_name),
+            )
+
+        return http_protocol
+
+    def test_http_request(self):
+        agent = ProxyAgent(self.reactor)
+
+        self.reactor.lookups["test.com"] = "1.2.3.4"
+        d = agent.request(b"GET", b"http://test.com")
+
+        # there should be a pending TCP connection
+        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, 80)
+
+        # make a test server, and wire up the client
+        http_server = self._make_connection(
+            client_factory, _get_test_protocol_factory()
+        )
+
+        # the FakeTransport is async, so we need to pump the reactor
+        self.reactor.advance(0)
+
+        # now there should be a pending request
+        self.assertEqual(len(http_server.requests), 1)
+
+        request = http_server.requests[0]
+        self.assertEqual(request.method, b"GET")
+        self.assertEqual(request.path, b"/")
+        self.assertEqual(request.requestHeaders.getRawHeaders(b"host"), [b"test.com"])
+        request.write(b"result")
+        request.finish()
+
+        self.reactor.advance(0)
+
+        resp = self.successResultOf(d)
+        body = self.successResultOf(treq.content(resp))
+        self.assertEqual(body, b"result")
+
+    def test_https_request(self):
+        agent = ProxyAgent(self.reactor, contextFactory=get_test_https_policy())
+
+        self.reactor.lookups["test.com"] = "1.2.3.4"
+        d = agent.request(b"GET", b"https://test.com/abc")
+
+        # there should be a pending TCP connection
+        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, 443)
+
+        # make a test server, and wire up the client
+        http_server = self._make_connection(
+            client_factory,
+            _get_test_protocol_factory(),
+            ssl=True,
+            expected_sni=b"test.com",
+        )
+
+        # the FakeTransport is async, so we need to pump the reactor
+        self.reactor.advance(0)
+
+        # now there should be a pending request
+        self.assertEqual(len(http_server.requests), 1)
+
+        request = http_server.requests[0]
+        self.assertEqual(request.method, b"GET")
+        self.assertEqual(request.path, b"/abc")
+        self.assertEqual(request.requestHeaders.getRawHeaders(b"host"), [b"test.com"])
+        request.write(b"result")
+        request.finish()
+
+        self.reactor.advance(0)
+
+        resp = self.successResultOf(d)
+        body = self.successResultOf(treq.content(resp))
+        self.assertEqual(body, b"result")
+
+    def test_http_request_via_proxy(self):
+        agent = ProxyAgent(self.reactor, http_proxy=b"proxy.com:8888")
+
+        self.reactor.lookups["proxy.com"] = "1.2.3.5"
+        d = agent.request(b"GET", b"http://test.com")
+
+        # there should be a pending TCP connection
+        clients = self.reactor.tcpClients
+        self.assertEqual(len(clients), 1)
+        (host, port, client_factory, _timeout, _bindAddress) = clients[0]
+        self.assertEqual(host, "1.2.3.5")
+        self.assertEqual(port, 8888)
+
+        # make a test server, and wire up the client
+        http_server = self._make_connection(
+            client_factory, _get_test_protocol_factory()
+        )
+
+        # the FakeTransport is async, so we need to pump the reactor
+        self.reactor.advance(0)
+
+        # now there should be a pending request
+        self.assertEqual(len(http_server.requests), 1)
+
+        request = http_server.requests[0]
+        self.assertEqual(request.method, b"GET")
+        self.assertEqual(request.path, b"http://test.com")
+        self.assertEqual(request.requestHeaders.getRawHeaders(b"host"), [b"test.com"])
+        request.write(b"result")
+        request.finish()
+
+        self.reactor.advance(0)
+
+        resp = self.successResultOf(d)
+        body = self.successResultOf(treq.content(resp))
+        self.assertEqual(body, b"result")
+
+    def test_https_request_via_proxy(self):
+        agent = ProxyAgent(
+            self.reactor,
+            contextFactory=get_test_https_policy(),
+            https_proxy=b"proxy.com",
+        )
+
+        self.reactor.lookups["proxy.com"] = "1.2.3.5"
+        d = agent.request(b"GET", b"https://test.com/abc")
+
+        # there should be a pending TCP connection
+        clients = self.reactor.tcpClients
+        self.assertEqual(len(clients), 1)
+        (host, port, client_factory, _timeout, _bindAddress) = clients[0]
+        self.assertEqual(host, "1.2.3.5")
+        self.assertEqual(port, 1080)
+
+        # make a test HTTP server, and wire up the client
+        proxy_server = self._make_connection(
+            client_factory, _get_test_protocol_factory()
+        )
+
+        # fish the transports back out so that we can do the old switcheroo
+        s2c_transport = proxy_server.transport
+        client_protocol = s2c_transport.other
+        c2s_transport = client_protocol.transport
+
+        # the FakeTransport is async, so we need to pump the reactor
+        self.reactor.advance(0)
+
+        # now there should be a pending CONNECT request
+        self.assertEqual(len(proxy_server.requests), 1)
+
+        request = proxy_server.requests[0]
+        self.assertEqual(request.method, b"CONNECT")
+        self.assertEqual(request.path, b"test.com:443")
+
+        # tell the proxy server not to close the connection
+        proxy_server.persistent = True
+
+        # this just stops the http Request trying to do a chunked response
+        # request.setHeader(b"Content-Length", b"0")
+        request.finish()
+
+        # now we can replace the proxy channel with a new, SSL-wrapped HTTP channel
+        ssl_factory = _wrap_server_factory_for_tls(_get_test_protocol_factory())
+        ssl_protocol = ssl_factory.buildProtocol(None)
+        http_server = ssl_protocol.wrappedProtocol
+
+        ssl_protocol.makeConnection(
+            FakeTransport(client_protocol, self.reactor, ssl_protocol)
+        )
+        c2s_transport.other = ssl_protocol
+
+        self.reactor.advance(0)
+
+        server_name = ssl_protocol._tlsConnection.get_servername()
+        expected_sni = b"test.com"
+        self.assertEqual(
+            server_name,
+            expected_sni,
+            "Expected SNI %s but got %s" % (expected_sni, server_name),
+        )
+
+        # now there should be a pending request
+        self.assertEqual(len(http_server.requests), 1)
+
+        request = http_server.requests[0]
+        self.assertEqual(request.method, b"GET")
+        self.assertEqual(request.path, b"/abc")
+        self.assertEqual(request.requestHeaders.getRawHeaders(b"host"), [b"test.com"])
+        request.write(b"result")
+        request.finish()
+
+        self.reactor.advance(0)
+
+        resp = self.successResultOf(d)
+        body = self.successResultOf(treq.content(resp))
+        self.assertEqual(body, b"result")
+
+
+def _wrap_server_factory_for_tls(factory, sanlist=None):
+    """Wrap an existing Protocol Factory with a test TLSMemoryBIOFactory
+
+    The resultant factory will create a TLS server which presents a certificate
+    signed by our test CA, valid for the domains in `sanlist`
+
+    Args:
+        factory (interfaces.IProtocolFactory): protocol factory to wrap
+        sanlist (iterable[bytes]): list of domains the cert should be valid for
+
+    Returns:
+        interfaces.IProtocolFactory
+    """
+    if sanlist is None:
+        sanlist = [b"DNS:test.com"]
+
+    connection_creator = TestServerTLSConnectionFactory(sanlist=sanlist)
+    return TLSMemoryBIOFactory(
+        connection_creator, isClient=False, wrappedFactory=factory
+    )
+
+
+def _get_test_protocol_factory():
+    """Get a protocol Factory which will build an HTTPChannel
+
+    Returns:
+        interfaces.IProtocolFactory
+    """
+    server_factory = Factory.forProtocol(HTTPChannel)
+
+    # Request.finish expects the factory to have a 'log' method.
+    server_factory.log = _log_request
+
+    return server_factory
+
+
+def _log_request(request):
+    """Implements Factory.log, which is expected by Request.finish"""
+    logger.info("Completed request %s", request)