# 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 base64
import logging
import os
from typing import Iterable, Optional
from unittest.mock import patch

import treq
from netaddr import IPSet
from parameterized import parameterized

from twisted.internet import interfaces  # noqa: F401
from twisted.internet.endpoints import HostnameEndpoint, _WrapperEndpoint
from twisted.internet.interfaces import IProtocol, IProtocolFactory
from twisted.internet.protocol import Factory
from twisted.protocols.tls import TLSMemoryBIOFactory, TLSMemoryBIOProtocol
from twisted.web.http import HTTPChannel

from synapse.http.client import BlacklistingReactorWrapper
from synapse.http.proxyagent import ProxyAgent, ProxyCredentials, parse_proxy

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 ProxyParserTests(TestCase):
    """
    Values for test
    [
        proxy_string,
        expected_scheme,
        expected_hostname,
        expected_port,
        expected_credentials,
    ]
    """

    @parameterized.expand(
        [
            # host
            [b"localhost", b"http", b"localhost", 1080, None],
            [b"localhost:9988", b"http", b"localhost", 9988, None],
            # host+scheme
            [b"https://localhost", b"https", b"localhost", 1080, None],
            [b"https://localhost:1234", b"https", b"localhost", 1234, None],
            # ipv4
            [b"1.2.3.4", b"http", b"1.2.3.4", 1080, None],
            [b"1.2.3.4:9988", b"http", b"1.2.3.4", 9988, None],
            # ipv4+scheme
            [b"https://1.2.3.4", b"https", b"1.2.3.4", 1080, None],
            [b"https://1.2.3.4:9988", b"https", b"1.2.3.4", 9988, None],
            # ipv6 - without brackets is broken
            # [
            #     b"2001:0db8:85a3:0000:0000:8a2e:0370:effe",
            #     b"http",
            #     b"2001:0db8:85a3:0000:0000:8a2e:0370:effe",
            #     1080,
            #     None,
            # ],
            # [
            #     b"2001:0db8:85a3:0000:0000:8a2e:0370:1234",
            #     b"http",
            #     b"2001:0db8:85a3:0000:0000:8a2e:0370:1234",
            #     1080,
            #     None,
            # ],
            # [b"::1", b"http", b"::1", 1080, None],
            # [b"::ffff:0.0.0.0", b"http", b"::ffff:0.0.0.0", 1080, None],
            # ipv6 - with brackets
            [
                b"[2001:0db8:85a3:0000:0000:8a2e:0370:effe]",
                b"http",
                b"2001:0db8:85a3:0000:0000:8a2e:0370:effe",
                1080,
                None,
            ],
            [
                b"[2001:0db8:85a3:0000:0000:8a2e:0370:1234]",
                b"http",
                b"2001:0db8:85a3:0000:0000:8a2e:0370:1234",
                1080,
                None,
            ],
            [b"[::1]", b"http", b"::1", 1080, None],
            [b"[::ffff:0.0.0.0]", b"http", b"::ffff:0.0.0.0", 1080, None],
            # ipv6+port
            [
                b"[2001:0db8:85a3:0000:0000:8a2e:0370:effe]:9988",
                b"http",
                b"2001:0db8:85a3:0000:0000:8a2e:0370:effe",
                9988,
                None,
            ],
            [
                b"[2001:0db8:85a3:0000:0000:8a2e:0370:1234]:9988",
                b"http",
                b"2001:0db8:85a3:0000:0000:8a2e:0370:1234",
                9988,
                None,
            ],
            [b"[::1]:9988", b"http", b"::1", 9988, None],
            [b"[::ffff:0.0.0.0]:9988", b"http", b"::ffff:0.0.0.0", 9988, None],
            # ipv6+scheme
            [
                b"https://[2001:0db8:85a3:0000:0000:8a2e:0370:effe]",
                b"https",
                b"2001:0db8:85a3:0000:0000:8a2e:0370:effe",
                1080,
                None,
            ],
            [
                b"https://[2001:0db8:85a3:0000:0000:8a2e:0370:1234]",
                b"https",
                b"2001:0db8:85a3:0000:0000:8a2e:0370:1234",
                1080,
                None,
            ],
            [b"https://[::1]", b"https", b"::1", 1080, None],
            [b"https://[::ffff:0.0.0.0]", b"https", b"::ffff:0.0.0.0", 1080, None],
            # ipv6+scheme+port
            [
                b"https://[2001:0db8:85a3:0000:0000:8a2e:0370:effe]:9988",
                b"https",
                b"2001:0db8:85a3:0000:0000:8a2e:0370:effe",
                9988,
                None,
            ],
            [
                b"https://[2001:0db8:85a3:0000:0000:8a2e:0370:1234]:9988",
                b"https",
                b"2001:0db8:85a3:0000:0000:8a2e:0370:1234",
                9988,
                None,
            ],
            [b"https://[::1]:9988", b"https", b"::1", 9988, None],
            # with credentials
            [
                b"https://user:pass@1.2.3.4:9988",
                b"https",
                b"1.2.3.4",
                9988,
                b"user:pass",
            ],
            [b"user:pass@1.2.3.4:9988", b"http", b"1.2.3.4", 9988, b"user:pass"],
            [
                b"https://user:pass@proxy.local:9988",
                b"https",
                b"proxy.local",
                9988,
                b"user:pass",
            ],
            [
                b"user:pass@proxy.local:9988",
                b"http",
                b"proxy.local",
                9988,
                b"user:pass",
            ],
        ]
    )
    def test_parse_proxy(
        self,
        proxy_string: bytes,
        expected_scheme: bytes,
        expected_hostname: bytes,
        expected_port: int,
        expected_credentials: Optional[bytes],
    ):
        """
        Tests that a given proxy URL will be broken into the components.
        Args:
            proxy_string: The proxy connection string.
            expected_scheme: Expected value of proxy scheme.
            expected_hostname: Expected value of proxy hostname.
            expected_port: Expected value of proxy port.
            expected_credentials: Expected value of credentials.
                Must be in form '<username>:<password>' or None
        """
        proxy_cred = None
        if expected_credentials:
            proxy_cred = ProxyCredentials(expected_credentials)
        self.assertEqual(
            (
                expected_scheme,
                expected_hostname,
                expected_port,
                proxy_cred,
            ),
            parse_proxy(proxy_string),
        )


class MatrixFederationAgentTests(TestCase):
    def setUp(self):
        self.reactor = ThreadedMemoryReactorClock()

    def _make_connection(
        self,
        client_factory: IProtocolFactory,
        server_factory: IProtocolFactory,
        ssl: bool = False,
        expected_sni: Optional[bytes] = None,
        tls_sanlist: Optional[Iterable[bytes]] = None,
    ) -> IProtocol:
        """Builds a test server, and completes the outgoing client connection

        Args:
            client_factory: 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: a factory to build the
                server-side protocol

            ssl: If true, we will expect an ssl connection and wrap
                server_factory with a TLSMemoryBIOFactory

            expected_sni: the expected SNI value

            tls_sanlist: list of SAN entries for the TLS cert presented by the server.
                 Defaults to [b'DNS:test.com']

        Returns:
            the server Protocol returned by server_factory
        """
        if ssl:
            server_factory = _wrap_server_factory_for_tls(server_factory, tls_sanlist)

        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,
                f"Expected SNI {expected_sni!s} but got {server_name!s}",
            )

        return http_protocol

    def _test_request_direct_connection(
        self,
        agent: ProxyAgent,
        scheme: bytes,
        hostname: bytes,
        path: bytes,
    ):
        """Runs a test case for a direct connection not going through a proxy.

        Args:
            agent: the proxy agent being tested

            scheme: expected to be either "http" or "https"

            hostname: the hostname to connect to in the test

            path: the path to connect to in the test
        """
        is_https = scheme == b"https"

        self.reactor.lookups[hostname.decode()] = "1.2.3.4"
        d = agent.request(b"GET", scheme + b"://" + hostname + b"/" + path)

        # 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 if is_https else 80)

        # make a test server, and wire up the client
        http_server = self._make_connection(
            client_factory,
            _get_test_protocol_factory(),
            ssl=is_https,
            expected_sni=hostname if is_https else None,
        )

        # 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"/" + path)
        self.assertEqual(request.requestHeaders.getRawHeaders(b"host"), [hostname])
        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(self):
        agent = ProxyAgent(self.reactor)
        self._test_request_direct_connection(agent, b"http", b"test.com", b"")

    def test_https_request(self):
        agent = ProxyAgent(self.reactor, contextFactory=get_test_https_policy())
        self._test_request_direct_connection(agent, b"https", b"test.com", b"abc")

    def test_http_request_use_proxy_empty_environment(self):
        agent = ProxyAgent(self.reactor, use_proxy=True)
        self._test_request_direct_connection(agent, b"http", b"test.com", b"")

    @patch.dict(os.environ, {"http_proxy": "proxy.com:8888", "NO_PROXY": "test.com"})
    def test_http_request_via_uppercase_no_proxy(self):
        agent = ProxyAgent(self.reactor, use_proxy=True)
        self._test_request_direct_connection(agent, b"http", b"test.com", b"")

    @patch.dict(
        os.environ, {"http_proxy": "proxy.com:8888", "no_proxy": "test.com,unused.com"}
    )
    def test_http_request_via_no_proxy(self):
        agent = ProxyAgent(self.reactor, use_proxy=True)
        self._test_request_direct_connection(agent, b"http", b"test.com", b"")

    @patch.dict(
        os.environ, {"https_proxy": "proxy.com", "no_proxy": "test.com,unused.com"}
    )
    def test_https_request_via_no_proxy(self):
        agent = ProxyAgent(
            self.reactor,
            contextFactory=get_test_https_policy(),
            use_proxy=True,
        )
        self._test_request_direct_connection(agent, b"https", b"test.com", b"abc")

    @patch.dict(os.environ, {"http_proxy": "proxy.com:8888", "no_proxy": "*"})
    def test_http_request_via_no_proxy_star(self):
        agent = ProxyAgent(self.reactor, use_proxy=True)
        self._test_request_direct_connection(agent, b"http", b"test.com", b"")

    @patch.dict(os.environ, {"https_proxy": "proxy.com", "no_proxy": "*"})
    def test_https_request_via_no_proxy_star(self):
        agent = ProxyAgent(
            self.reactor,
            contextFactory=get_test_https_policy(),
            use_proxy=True,
        )
        self._test_request_direct_connection(agent, b"https", b"test.com", b"abc")

    @patch.dict(os.environ, {"http_proxy": "proxy.com:8888", "no_proxy": "unused.com"})
    def test_http_request_via_proxy(self):
        """
        Tests that requests can be made through a proxy.
        """
        self._do_http_request_via_proxy(ssl=False, auth_credentials=None)

    @patch.dict(
        os.environ,
        {"http_proxy": "bob:pinkponies@proxy.com:8888", "no_proxy": "unused.com"},
    )
    def test_http_request_via_proxy_with_auth(self):
        """
        Tests that authenticated requests can be made through a proxy.
        """
        self._do_http_request_via_proxy(ssl=False, auth_credentials=b"bob:pinkponies")

    @patch.dict(
        os.environ, {"http_proxy": "https://proxy.com:8888", "no_proxy": "unused.com"}
    )
    def test_http_request_via_https_proxy(self):
        self._do_http_request_via_proxy(ssl=True, auth_credentials=None)

    @patch.dict(
        os.environ,
        {
            "http_proxy": "https://bob:pinkponies@proxy.com:8888",
            "no_proxy": "unused.com",
        },
    )
    def test_http_request_via_https_proxy_with_auth(self):
        self._do_http_request_via_proxy(ssl=True, auth_credentials=b"bob:pinkponies")

    @patch.dict(os.environ, {"https_proxy": "proxy.com", "no_proxy": "unused.com"})
    def test_https_request_via_proxy(self):
        """Tests that TLS-encrypted requests can be made through a proxy"""
        self._do_https_request_via_proxy(ssl=False, auth_credentials=None)

    @patch.dict(
        os.environ,
        {"https_proxy": "bob:pinkponies@proxy.com", "no_proxy": "unused.com"},
    )
    def test_https_request_via_proxy_with_auth(self):
        """Tests that authenticated, TLS-encrypted requests can be made through a proxy"""
        self._do_https_request_via_proxy(ssl=False, auth_credentials=b"bob:pinkponies")

    @patch.dict(
        os.environ, {"https_proxy": "https://proxy.com", "no_proxy": "unused.com"}
    )
    def test_https_request_via_https_proxy(self):
        """Tests that TLS-encrypted requests can be made through a proxy"""
        self._do_https_request_via_proxy(ssl=True, auth_credentials=None)

    @patch.dict(
        os.environ,
        {"https_proxy": "https://bob:pinkponies@proxy.com", "no_proxy": "unused.com"},
    )
    def test_https_request_via_https_proxy_with_auth(self):
        """Tests that authenticated, TLS-encrypted requests can be made through a proxy"""
        self._do_https_request_via_proxy(ssl=True, auth_credentials=b"bob:pinkponies")

    def _do_http_request_via_proxy(
        self,
        ssl: bool = False,
        auth_credentials: Optional[bytes] = None,
    ):
        """Send a http request via an agent and check that it is correctly received at
            the proxy. The proxy can use either http or https.
        Args:
            ssl: True if we expect the request to connect via https to proxy
            auth_credentials: credentials to authenticate at proxy
        """
        if ssl:
            agent = ProxyAgent(
                self.reactor, use_proxy=True, contextFactory=get_test_https_policy()
            )
        else:
            agent = ProxyAgent(self.reactor, use_proxy=True)

        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(),
            ssl=ssl,
            tls_sanlist=[b"DNS:proxy.com"] if ssl else None,
            expected_sni=b"proxy.com" if ssl else None,
        )

        # 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]

        # Check whether auth credentials have been supplied to the proxy
        proxy_auth_header_values = request.requestHeaders.getRawHeaders(
            b"Proxy-Authorization"
        )

        if auth_credentials is not None:
            # Compute the correct header value for Proxy-Authorization
            encoded_credentials = base64.b64encode(auth_credentials)
            expected_header_value = b"Basic " + encoded_credentials

            # Validate the header's value
            self.assertIn(expected_header_value, proxy_auth_header_values)
        else:
            # Check that the Proxy-Authorization header has not been supplied to the proxy
            self.assertIsNone(proxy_auth_header_values)

        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 _do_https_request_via_proxy(
        self,
        ssl: bool = False,
        auth_credentials: Optional[bytes] = None,
    ):
        """Send a https request via an agent and check that it is correctly received at
            the proxy and client. The proxy can use either http or https.
        Args:
            ssl: True if we expect the request to connect via https to proxy
            auth_credentials: credentials to authenticate at proxy
        """
        agent = ProxyAgent(
            self.reactor,
            contextFactory=get_test_https_policy(),
            use_proxy=True,
        )

        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 server to act as the proxy, and wire up the client
        proxy_server = self._make_connection(
            client_factory,
            _get_test_protocol_factory(),
            ssl=ssl,
            tls_sanlist=[b"DNS:proxy.com"] if ssl else None,
            expected_sni=b"proxy.com" if ssl else None,
        )
        assert isinstance(proxy_server, HTTPChannel)

        # 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")

        # Check whether auth credentials have been supplied to the proxy
        proxy_auth_header_values = request.requestHeaders.getRawHeaders(
            b"Proxy-Authorization"
        )

        if auth_credentials is not None:
            # Compute the correct header value for Proxy-Authorization
            encoded_credentials = base64.b64encode(auth_credentials)
            expected_header_value = b"Basic " + encoded_credentials

            # Validate the header's value
            self.assertIn(expected_header_value, proxy_auth_header_values)
        else:
            # Check that the Proxy-Authorization header has not been supplied to the proxy
            self.assertIsNone(proxy_auth_header_values)

        # tell the proxy server not to close the connection
        proxy_server.persistent = True

        request.finish()

        # now we make another test server to act as the upstream HTTP server.
        server_ssl_protocol = _wrap_server_factory_for_tls(
            _get_test_protocol_factory()
        ).buildProtocol(None)

        # Tell the HTTP server to send outgoing traffic back via the proxy's transport.
        proxy_server_transport = proxy_server.transport
        server_ssl_protocol.makeConnection(proxy_server_transport)

        # ... and replace the protocol on the proxy's transport with the
        # TLSMemoryBIOProtocol for the test server, so that incoming traffic
        # to the proxy gets sent over to the HTTP(s) server.
        #
        # This needs a bit of gut-wrenching, which is different depending on whether
        # the proxy is using TLS or not.
        #
        # (an alternative, possibly more elegant, approach would be to use a custom
        # Protocol to implement the proxy, which starts out by forwarding to an
        # HTTPChannel (to implement the CONNECT command) and can then be switched
        # into a mode where it forwards its traffic to another Protocol.)
        if ssl:
            assert isinstance(proxy_server_transport, TLSMemoryBIOProtocol)
            proxy_server_transport.wrappedProtocol = server_ssl_protocol
        else:
            assert isinstance(proxy_server_transport, FakeTransport)
            client_protocol = proxy_server_transport.other
            c2s_transport = client_protocol.transport
            c2s_transport.other = server_ssl_protocol

        self.reactor.advance(0)

        server_name = server_ssl_protocol._tlsConnection.get_servername()
        expected_sni = b"test.com"
        self.assertEqual(
            server_name,
            expected_sni,
            f"Expected SNI {expected_sni!s} but got {server_name!s}",
        )

        # now there should be a pending request
        http_server = server_ssl_protocol.wrappedProtocol
        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"])

        # Check that the destination server DID NOT receive proxy credentials
        proxy_auth_header_values = request.requestHeaders.getRawHeaders(
            b"Proxy-Authorization"
        )
        self.assertIsNone(proxy_auth_header_values)

        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")

    @patch.dict(os.environ, {"http_proxy": "proxy.com:8888"})
    def test_http_request_via_proxy_with_blacklist(self):
        # The blacklist includes the configured proxy IP.
        agent = ProxyAgent(
            BlacklistingReactorWrapper(
                self.reactor, ip_whitelist=None, ip_blacklist=IPSet(["1.0.0.0/8"])
            ),
            self.reactor,
            use_proxy=True,
        )

        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")

    @patch.dict(os.environ, {"HTTPS_PROXY": "proxy.com"})
    def test_https_request_via_uppercase_proxy_with_blacklist(self):
        # The blacklist includes the configured proxy IP.
        agent = ProxyAgent(
            BlacklistingReactorWrapper(
                self.reactor, ip_whitelist=None, ip_blacklist=IPSet(["1.0.0.0/8"])
            ),
            self.reactor,
            contextFactory=get_test_https_policy(),
            use_proxy=True,
        )

        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,
            f"Expected SNI {expected_sni!s} but got {server_name!s}",
        )

        # 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")

    @patch.dict(os.environ, {"http_proxy": "proxy.com:8888"})
    def test_proxy_with_no_scheme(self):
        http_proxy_agent = ProxyAgent(self.reactor, use_proxy=True)
        self.assertIsInstance(http_proxy_agent.http_proxy_endpoint, HostnameEndpoint)
        self.assertEqual(http_proxy_agent.http_proxy_endpoint._hostStr, "proxy.com")
        self.assertEqual(http_proxy_agent.http_proxy_endpoint._port, 8888)

    @patch.dict(os.environ, {"http_proxy": "socks://proxy.com:8888"})
    def test_proxy_with_unsupported_scheme(self):
        with self.assertRaises(ValueError):
            ProxyAgent(self.reactor, use_proxy=True)

    @patch.dict(os.environ, {"http_proxy": "http://proxy.com:8888"})
    def test_proxy_with_http_scheme(self):
        http_proxy_agent = ProxyAgent(self.reactor, use_proxy=True)
        self.assertIsInstance(http_proxy_agent.http_proxy_endpoint, HostnameEndpoint)
        self.assertEqual(http_proxy_agent.http_proxy_endpoint._hostStr, "proxy.com")
        self.assertEqual(http_proxy_agent.http_proxy_endpoint._port, 8888)

    @patch.dict(os.environ, {"http_proxy": "https://proxy.com:8888"})
    def test_proxy_with_https_scheme(self):
        https_proxy_agent = ProxyAgent(self.reactor, use_proxy=True)
        self.assertIsInstance(https_proxy_agent.http_proxy_endpoint, _WrapperEndpoint)
        self.assertEqual(
            https_proxy_agent.http_proxy_endpoint._wrappedEndpoint._hostStr, "proxy.com"
        )
        self.assertEqual(
            https_proxy_agent.http_proxy_endpoint._wrappedEndpoint._port, 8888
        )


def _wrap_server_factory_for_tls(
    factory: IProtocolFactory, sanlist: Iterable[bytes] = None
) -> IProtocolFactory:
    """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: protocol factory to wrap
        sanlist: 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() -> IProtocolFactory:
    """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: str):
    """Implements Factory.log, which is expected by Request.finish"""
    logger.info(f"Completed request {request}")