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.

1 files changed, 195 insertions, 0 deletions

diff --git a/synapse/http/proxyagent.py b/synapse/http/proxyagent.py
new file mode 100644
index 0000000000..332da02a8d
--- /dev/null
+++ b/synapse/http/proxyagent.py
@@ -0,0 +1,195 @@
+# -*- 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 re
+
+from zope.interface import implementer
+
+from twisted.internet import defer
+from twisted.internet.endpoints import HostnameEndpoint, wrapClientTLS
+from twisted.python.failure import Failure
+from twisted.web.client import URI, BrowserLikePolicyForHTTPS, _AgentBase
+from twisted.web.error import SchemeNotSupported
+from twisted.web.iweb import IAgent
+
+from synapse.http.connectproxyclient import HTTPConnectProxyEndpoint
+
+logger = logging.getLogger(__name__)
+
+_VALID_URI = re.compile(br"\A[\x21-\x7e]+\Z")
+
+
+@implementer(IAgent)
+class ProxyAgent(_AgentBase):
+    """An Agent implementation which will use an HTTP proxy if one was requested
+
+    Args:
+        reactor: twisted reactor to place outgoing
+            connections.
+
+        contextFactory (IPolicyForHTTPS): A factory for TLS contexts, to control the
+            verification parameters of OpenSSL.  The default is to use a
+            `BrowserLikePolicyForHTTPS`, so unless you have special
+            requirements you can leave this as-is.
+
+        connectTimeout (float): The amount of time that this Agent will wait
+            for the peer to accept a connection.
+
+        bindAddress (bytes): The local address for client sockets to bind to.
+
+        pool (HTTPConnectionPool|None): connection pool to be used. If None, a
+            non-persistent pool instance will be created.
+    """
+
+    def __init__(
+        self,
+        reactor,
+        contextFactory=BrowserLikePolicyForHTTPS(),
+        connectTimeout=None,
+        bindAddress=None,
+        pool=None,
+        http_proxy=None,
+        https_proxy=None,
+    ):
+        _AgentBase.__init__(self, reactor, pool)
+
+        self._endpoint_kwargs = {}
+        if connectTimeout is not None:
+            self._endpoint_kwargs["timeout"] = connectTimeout
+        if bindAddress is not None:
+            self._endpoint_kwargs["bindAddress"] = bindAddress
+
+        self.http_proxy_endpoint = _http_proxy_endpoint(
+            http_proxy, reactor, **self._endpoint_kwargs
+        )
+
+        self.https_proxy_endpoint = _http_proxy_endpoint(
+            https_proxy, reactor, **self._endpoint_kwargs
+        )
+
+        self._policy_for_https = contextFactory
+        self._reactor = reactor
+
+    def request(self, method, uri, headers=None, bodyProducer=None):
+        """
+        Issue a request to the server indicated by the given uri.
+
+        Supports `http` and `https` schemes.
+
+        An existing connection from the connection pool may be used or a new one may be
+        created.
+
+        See also: twisted.web.iweb.IAgent.request
+
+        Args:
+            method (bytes): The request method to use, such as `GET`, `POST`, etc
+
+            uri (bytes): The location of the resource to request.
+
+            headers (Headers|None): Extra headers to send with the request
+
+            bodyProducer (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[IResponse]: completes when the header of the response has
+                 been received (regardless of the response status code).
+        """
+        uri = uri.strip()
+        if not _VALID_URI.match(uri):
+            raise ValueError("Invalid URI {!r}".format(uri))
+
+        parsed_uri = URI.fromBytes(uri)
+        pool_key = (parsed_uri.scheme, parsed_uri.host, parsed_uri.port)
+        request_path = parsed_uri.originForm
+
+        if parsed_uri.scheme == b"http" and self.http_proxy_endpoint:
+            # Cache *all* connections under the same key, since we are only
+            # connecting to a single destination, the proxy:
+            pool_key = ("http-proxy", self.http_proxy_endpoint)
+            endpoint = self.http_proxy_endpoint
+            request_path = uri
+        elif parsed_uri.scheme == b"https" and self.https_proxy_endpoint:
+            endpoint = HTTPConnectProxyEndpoint(
+                self._reactor,
+                self.https_proxy_endpoint,
+                parsed_uri.host,
+                parsed_uri.port,
+            )
+        else:
+            # not using a proxy
+            endpoint = HostnameEndpoint(
+                self._reactor, parsed_uri.host, parsed_uri.port, **self._endpoint_kwargs
+            )
+
+        logger.debug("Requesting %s via %s", uri, endpoint)
+
+        if parsed_uri.scheme == b"https":
+            tls_connection_creator = self._policy_for_https.creatorForNetloc(
+                parsed_uri.host, parsed_uri.port
+            )
+            endpoint = wrapClientTLS(tls_connection_creator, endpoint)
+        elif parsed_uri.scheme == b"http":
+            pass
+        else:
+            return defer.fail(
+                Failure(
+                    SchemeNotSupported("Unsupported scheme: %r" % (parsed_uri.scheme,))
+                )
+            )
+
+        return self._requestWithEndpoint(
+            pool_key, endpoint, method, parsed_uri, headers, bodyProducer, request_path
+        )
+
+
+def _http_proxy_endpoint(proxy, reactor, **kwargs):
+    """Parses an http proxy setting and returns an endpoint for the proxy
+
+    Args:
+        proxy (bytes|None):  the proxy setting
+        reactor: reactor to be used to connect to the proxy
+        kwargs: other args to be passed to HostnameEndpoint
+
+    Returns:
+        interfaces.IStreamClientEndpoint|None: endpoint to use to connect to the proxy,
+            or None
+    """
+    if proxy is None:
+        return None
+
+    # currently we only support hostname:port. Some apps also support
+    # protocol://<host>[:port], which allows a way of requiring a TLS connection to the
+    # proxy.
+
+    host, port = parse_host_port(proxy, default_port=1080)
+    return HostnameEndpoint(reactor, host, port, **kwargs)
+
+
+def parse_host_port(hostport, default_port=None):
+    # could have sworn we had one of these somewhere else...
+    if b":" in hostport:
+        host, port = hostport.rsplit(b":", 1)
+        try:
+            port = int(port)
+            return host, port
+        except ValueError:
+            # the thing after the : wasn't a valid port; presumably this is an
+            # IPv6 address.
+            pass
+
+    return hostport, default_port