RISCI_ATOM
/
synapse
mirror of https://github.com/matrix-org/synapse.git


			
							123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358359360361362363364365366367368369370371372373374375376377378379380381382383384385386387388389390391392393394395396397398399400401402403404405406407408409410411412413414415416417418419420421422423424425426427428429430431432433434435436437438439440441442443444445446447448449450451452453454455456457458459460461462463464465466467468469470471472473474475476477478479480481482483484485486487488489490491492493494495496497498499500501502503504505506507508509510511512513514515516517518519520521522523524525526527528529530531532533534535536537538539540541542543544545546547548549550551552553554555556557558559560561562563564565566567568569570571572573574575576577578579580581582583584585586587588589590591592593594595596597598599600601602603604605606607608609610611612613614615616617618619620621622623624625626627628629630631632633634635636637638639640641642643644645646647648649650651652653654655656657658659660661662663664665666667668669670671672673674675676677678679680681682683684685686687688689690691692693694695696697698699700701702703704705706707708709710711712713714715716717718719720721722723724725726727728729730731732733734735736737738739740741742743744745746747748749750751752753754755756757758759760761762763764765766767768769770771772773774775776777778779780781782783784785786787788789790791792793794795796797798799800801802803804805806807808809810811812813814815816817818819820821822823824825826827828829830831832833834835836837838839840841842843844845846847848849850851852853854855856857858859860861862863864865866867868869870871872873874875876877878879880881882883884885886887888889890891892893894895896897898899900901902903904905906907908909910911912913914915916917918919920921922923924925926927928929930931932933934935936937938939940941942943944945946947948949950951952953954955956957958959960961962963964965966967968969970971972973974975976977978979980981982983
							# Copyright 2018 New Vector Ltd
# Copyright 2021 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 json
import os
import re

from twisted.internet._resolver import HostResolution
from twisted.internet.address import IPv4Address, IPv6Address
from twisted.internet.error import DNSLookupError
from twisted.test.proto_helpers import AccumulatingProtocol

from synapse.config.oembed import OEmbedEndpointConfig
from synapse.rest.media.v1.preview_url_resource import IMAGE_CACHE_EXPIRY_MS
from synapse.util.stringutils import parse_and_validate_mxc_uri

from tests import unittest
from tests.server import FakeTransport
from tests.test_utils import SMALL_PNG
from tests.utils import MockClock

try:
    import lxml
except ImportError:
    lxml = None


class URLPreviewTests(unittest.HomeserverTestCase):
    if not lxml:
        skip = "url preview feature requires lxml"

    hijack_auth = True
    user_id = "@test:user"
    end_content = (
        b"<html><head>"
        b'<meta property="og:title" content="~matrix~" />'
        b'<meta property="og:description" content="hi" />'
        b"</head></html>"
    )

    def make_homeserver(self, reactor, clock):

        config = self.default_config()
        config["url_preview_enabled"] = True
        config["max_spider_size"] = 9999999
        config["url_preview_ip_range_blacklist"] = (
            "192.168.1.1",
            "1.0.0.0/8",
            "3fff:ffff:ffff:ffff:ffff:ffff:ffff:ffff",
            "2001:800::/21",
        )
        config["url_preview_ip_range_whitelist"] = ("1.1.1.1",)
        config["url_preview_url_blacklist"] = []
        config["url_preview_accept_language"] = [
            "en-UK",
            "en-US;q=0.9",
            "fr;q=0.8",
            "*;q=0.7",
        ]

        self.storage_path = self.mktemp()
        self.media_store_path = self.mktemp()
        os.mkdir(self.storage_path)
        os.mkdir(self.media_store_path)
        config["media_store_path"] = self.media_store_path

        provider_config = {
            "module": "synapse.rest.media.v1.storage_provider.FileStorageProviderBackend",
            "store_local": True,
            "store_synchronous": False,
            "store_remote": True,
            "config": {"directory": self.storage_path},
        }

        config["media_storage_providers"] = [provider_config]

        hs = self.setup_test_homeserver(config=config)

        # After the hs is created, modify the parsed oEmbed config (to avoid
        # messing with files).
        #
        # Note that HTTP URLs are used to avoid having to deal with TLS in tests.
        hs.config.oembed.oembed_patterns = [
            OEmbedEndpointConfig(
                api_endpoint="http://publish.twitter.com/oembed",
                url_patterns=[
                    re.compile(r"http://twitter\.com/.+/status/.+"),
                ],
                formats=None,
            ),
            OEmbedEndpointConfig(
                api_endpoint="http://www.hulu.com/api/oembed.{format}",
                url_patterns=[
                    re.compile(r"http://www\.hulu\.com/watch/.+"),
                ],
                formats=["json"],
            ),
        ]

        return hs

    def prepare(self, reactor, clock, hs):

        self.media_repo = hs.get_media_repository_resource()
        self.preview_url = self.media_repo.children[b"preview_url"]

        self.lookups = {}

        class Resolver:
            def resolveHostName(
                _self,
                resolutionReceiver,
                hostName,
                portNumber=0,
                addressTypes=None,
                transportSemantics="TCP",
            ):

                resolution = HostResolution(hostName)
                resolutionReceiver.resolutionBegan(resolution)
                if hostName not in self.lookups:
                    raise DNSLookupError("OH NO")

                for i in self.lookups[hostName]:
                    resolutionReceiver.addressResolved(i[0]("TCP", i[1], portNumber))
                resolutionReceiver.resolutionComplete()
                return resolutionReceiver

        self.reactor.nameResolver = Resolver()

    def create_test_resource(self):
        return self.hs.get_media_repository_resource()

    def test_cache_returns_correct_type(self):
        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]

        channel = self.make_request(
            "GET",
            "preview_url?url=http://matrix.org",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        client = self.reactor.tcpClients[0][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\nContent-Type: text/html\r\n\r\n"
            % (len(self.end_content),)
            + self.end_content
        )

        self.pump()
        self.assertEqual(channel.code, 200)
        self.assertEqual(
            channel.json_body, {"og:title": "~matrix~", "og:description": "hi"}
        )

        # Check the cache returns the correct response
        channel = self.make_request(
            "GET", "preview_url?url=http://matrix.org", shorthand=False
        )

        # Check the cache response has the same content
        self.assertEqual(channel.code, 200)
        self.assertEqual(
            channel.json_body, {"og:title": "~matrix~", "og:description": "hi"}
        )

        # Clear the in-memory cache
        self.assertIn("http://matrix.org", self.preview_url._cache)
        self.preview_url._cache.pop("http://matrix.org")
        self.assertNotIn("http://matrix.org", self.preview_url._cache)

        # Check the database cache returns the correct response
        channel = self.make_request(
            "GET", "preview_url?url=http://matrix.org", shorthand=False
        )

        # Check the cache response has the same content
        self.assertEqual(channel.code, 200)
        self.assertEqual(
            channel.json_body, {"og:title": "~matrix~", "og:description": "hi"}
        )

    def test_non_ascii_preview_httpequiv(self):
        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]

        end_content = (
            b"<html><head>"
            b'<meta http-equiv="Content-Type" content="text/html; charset=windows-1251"/>'
            b'<meta property="og:title" content="\xe4\xea\xe0" />'
            b'<meta property="og:description" content="hi" />'
            b"</head></html>"
        )

        channel = self.make_request(
            "GET",
            "preview_url?url=http://matrix.org",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        client = self.reactor.tcpClients[0][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            (
                b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
                b'Content-Type: text/html; charset="utf8"\r\n\r\n'
            )
            % (len(end_content),)
            + end_content
        )

        self.pump()
        self.assertEqual(channel.code, 200)
        self.assertEqual(channel.json_body["og:title"], "\u0434\u043a\u0430")

    def test_non_ascii_preview_content_type(self):
        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]

        end_content = (
            b"<html><head>"
            b'<meta property="og:title" content="\xe4\xea\xe0" />'
            b'<meta property="og:description" content="hi" />'
            b"</head></html>"
        )

        channel = self.make_request(
            "GET",
            "preview_url?url=http://matrix.org",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        client = self.reactor.tcpClients[0][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            (
                b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
                b'Content-Type: text/html; charset="windows-1251"\r\n\r\n'
            )
            % (len(end_content),)
            + end_content
        )

        self.pump()
        self.assertEqual(channel.code, 200)
        self.assertEqual(channel.json_body["og:title"], "\u0434\u043a\u0430")

    def test_overlong_title(self):
        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]

        end_content = (
            b"<html><head>"
            b"<title>" + b"x" * 2000 + b"</title>"
            b'<meta property="og:description" content="hi" />'
            b"</head></html>"
        )

        channel = self.make_request(
            "GET",
            "preview_url?url=http://matrix.org",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        client = self.reactor.tcpClients[0][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            (
                b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
                b'Content-Type: text/html; charset="windows-1251"\r\n\r\n'
            )
            % (len(end_content),)
            + end_content
        )

        self.pump()
        self.assertEqual(channel.code, 200)
        res = channel.json_body
        # We should only see the `og:description` field, as `title` is too long and should be stripped out
        self.assertCountEqual(["og:description"], res.keys())

    def test_ipaddr(self):
        """
        IP addresses can be previewed directly.
        """
        self.lookups["example.com"] = [(IPv4Address, "10.1.2.3")]

        channel = self.make_request(
            "GET",
            "preview_url?url=http://example.com",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        client = self.reactor.tcpClients[0][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\nContent-Type: text/html\r\n\r\n"
            % (len(self.end_content),)
            + self.end_content
        )

        self.pump()
        self.assertEqual(channel.code, 200)
        self.assertEqual(
            channel.json_body, {"og:title": "~matrix~", "og:description": "hi"}
        )

    def test_blacklisted_ip_specific(self):
        """
        Blacklisted IP addresses, found via DNS, are not spidered.
        """
        self.lookups["example.com"] = [(IPv4Address, "192.168.1.1")]

        channel = self.make_request(
            "GET", "preview_url?url=http://example.com", shorthand=False
        )

        # No requests made.
        self.assertEqual(len(self.reactor.tcpClients), 0)
        self.assertEqual(channel.code, 502)
        self.assertEqual(
            channel.json_body,
            {
                "errcode": "M_UNKNOWN",
                "error": "DNS resolution failure during URL preview generation",
            },
        )

    def test_blacklisted_ip_range(self):
        """
        Blacklisted IP ranges, IPs found over DNS, are not spidered.
        """
        self.lookups["example.com"] = [(IPv4Address, "1.1.1.2")]

        channel = self.make_request(
            "GET", "preview_url?url=http://example.com", shorthand=False
        )

        self.assertEqual(channel.code, 502)
        self.assertEqual(
            channel.json_body,
            {
                "errcode": "M_UNKNOWN",
                "error": "DNS resolution failure during URL preview generation",
            },
        )

    def test_blacklisted_ip_specific_direct(self):
        """
        Blacklisted IP addresses, accessed directly, are not spidered.
        """
        channel = self.make_request(
            "GET", "preview_url?url=http://192.168.1.1", shorthand=False
        )

        # No requests made.
        self.assertEqual(len(self.reactor.tcpClients), 0)
        self.assertEqual(
            channel.json_body,
            {
                "errcode": "M_UNKNOWN",
                "error": "IP address blocked by IP blacklist entry",
            },
        )
        self.assertEqual(channel.code, 403)

    def test_blacklisted_ip_range_direct(self):
        """
        Blacklisted IP ranges, accessed directly, are not spidered.
        """
        channel = self.make_request(
            "GET", "preview_url?url=http://1.1.1.2", shorthand=False
        )

        self.assertEqual(channel.code, 403)
        self.assertEqual(
            channel.json_body,
            {
                "errcode": "M_UNKNOWN",
                "error": "IP address blocked by IP blacklist entry",
            },
        )

    def test_blacklisted_ip_range_whitelisted_ip(self):
        """
        Blacklisted but then subsequently whitelisted IP addresses can be
        spidered.
        """
        self.lookups["example.com"] = [(IPv4Address, "1.1.1.1")]

        channel = self.make_request(
            "GET",
            "preview_url?url=http://example.com",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        client = self.reactor.tcpClients[0][2].buildProtocol(None)

        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))

        client.dataReceived(
            b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\nContent-Type: text/html\r\n\r\n"
            % (len(self.end_content),)
            + self.end_content
        )

        self.pump()
        self.assertEqual(channel.code, 200)
        self.assertEqual(
            channel.json_body, {"og:title": "~matrix~", "og:description": "hi"}
        )

    def test_blacklisted_ip_with_external_ip(self):
        """
        If a hostname resolves a blacklisted IP, even if there's a
        non-blacklisted one, it will be rejected.
        """
        # Hardcode the URL resolving to the IP we want.
        self.lookups["example.com"] = [
            (IPv4Address, "1.1.1.2"),
            (IPv4Address, "10.1.2.3"),
        ]

        channel = self.make_request(
            "GET", "preview_url?url=http://example.com", shorthand=False
        )
        self.assertEqual(channel.code, 502)
        self.assertEqual(
            channel.json_body,
            {
                "errcode": "M_UNKNOWN",
                "error": "DNS resolution failure during URL preview generation",
            },
        )

    def test_blacklisted_ipv6_specific(self):
        """
        Blacklisted IP addresses, found via DNS, are not spidered.
        """
        self.lookups["example.com"] = [
            (IPv6Address, "3fff:ffff:ffff:ffff:ffff:ffff:ffff:ffff")
        ]

        channel = self.make_request(
            "GET", "preview_url?url=http://example.com", shorthand=False
        )

        # No requests made.
        self.assertEqual(len(self.reactor.tcpClients), 0)
        self.assertEqual(channel.code, 502)
        self.assertEqual(
            channel.json_body,
            {
                "errcode": "M_UNKNOWN",
                "error": "DNS resolution failure during URL preview generation",
            },
        )

    def test_blacklisted_ipv6_range(self):
        """
        Blacklisted IP ranges, IPs found over DNS, are not spidered.
        """
        self.lookups["example.com"] = [(IPv6Address, "2001:800::1")]

        channel = self.make_request(
            "GET", "preview_url?url=http://example.com", shorthand=False
        )

        self.assertEqual(channel.code, 502)
        self.assertEqual(
            channel.json_body,
            {
                "errcode": "M_UNKNOWN",
                "error": "DNS resolution failure during URL preview generation",
            },
        )

    def test_OPTIONS(self):
        """
        OPTIONS returns the OPTIONS.
        """
        channel = self.make_request(
            "OPTIONS", "preview_url?url=http://example.com", shorthand=False
        )
        self.assertEqual(channel.code, 200)
        self.assertEqual(channel.json_body, {})

    def test_accept_language_config_option(self):
        """
        Accept-Language header is sent to the remote server
        """
        self.lookups["example.com"] = [(IPv4Address, "10.1.2.3")]

        # Build and make a request to the server
        channel = self.make_request(
            "GET",
            "preview_url?url=http://example.com",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        # Extract Synapse's tcp client
        client = self.reactor.tcpClients[0][2].buildProtocol(None)

        # Build a fake remote server to reply with
        server = AccumulatingProtocol()

        # Connect the two together
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))

        # Tell Synapse that it has received some data from the remote server
        client.dataReceived(
            b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\nContent-Type: text/html\r\n\r\n"
            % (len(self.end_content),)
            + self.end_content
        )

        # Move the reactor along until we get a response on our original channel
        self.pump()
        self.assertEqual(channel.code, 200)
        self.assertEqual(
            channel.json_body, {"og:title": "~matrix~", "og:description": "hi"}
        )

        # Check that the server received the Accept-Language header as part
        # of the request from Synapse
        self.assertIn(
            (
                b"Accept-Language: en-UK\r\n"
                b"Accept-Language: en-US;q=0.9\r\n"
                b"Accept-Language: fr;q=0.8\r\n"
                b"Accept-Language: *;q=0.7"
            ),
            server.data,
        )

    def test_oembed_photo(self):
        """Test an oEmbed endpoint which returns a 'photo' type which redirects the preview to a new URL."""
        self.lookups["publish.twitter.com"] = [(IPv4Address, "10.1.2.3")]
        self.lookups["cdn.twitter.com"] = [(IPv4Address, "10.1.2.3")]

        result = {
            "version": "1.0",
            "type": "photo",
            "url": "http://cdn.twitter.com/matrixdotorg",
        }
        oembed_content = json.dumps(result).encode("utf-8")

        channel = self.make_request(
            "GET",
            "preview_url?url=http://twitter.com/matrixdotorg/status/12345",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        client = self.reactor.tcpClients[0][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            (
                b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
                b'Content-Type: application/json; charset="utf8"\r\n\r\n'
            )
            % (len(oembed_content),)
            + oembed_content
        )

        self.pump()

        # Ensure a second request is made to the photo URL.
        client = self.reactor.tcpClients[1][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            (
                b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
                b"Content-Type: image/png\r\n\r\n"
            )
            % (len(SMALL_PNG),)
            + SMALL_PNG
        )

        self.pump()

        # Ensure the URL is what was requested.
        self.assertIn(b"/matrixdotorg", server.data)

        self.assertEqual(channel.code, 200)
        body = channel.json_body
        self.assertEqual(body["og:url"], "http://twitter.com/matrixdotorg/status/12345")
        self.assertTrue(body["og:image"].startswith("mxc://"))
        self.assertEqual(body["og:image:height"], 1)
        self.assertEqual(body["og:image:width"], 1)
        self.assertEqual(body["og:image:type"], "image/png")

    def test_oembed_rich(self):
        """Test an oEmbed endpoint which returns HTML content via the 'rich' type."""
        self.lookups["publish.twitter.com"] = [(IPv4Address, "10.1.2.3")]

        result = {
            "version": "1.0",
            "type": "rich",
            # Note that this provides the author, not the title.
            "author_name": "Alice",
            "html": "<div>Content Preview</div>",
        }
        end_content = json.dumps(result).encode("utf-8")

        channel = self.make_request(
            "GET",
            "preview_url?url=http://twitter.com/matrixdotorg/status/12345",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        client = self.reactor.tcpClients[0][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            (
                b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
                b'Content-Type: application/json; charset="utf8"\r\n\r\n'
            )
            % (len(end_content),)
            + end_content
        )

        self.pump()
        self.assertEqual(channel.code, 200)
        body = channel.json_body
        self.assertEqual(
            body,
            {
                "og:url": "http://twitter.com/matrixdotorg/status/12345",
                "og:title": "Alice",
                "og:description": "Content Preview",
            },
        )

    def test_oembed_format(self):
        """Test an oEmbed endpoint which requires the format in the URL."""
        self.lookups["www.hulu.com"] = [(IPv4Address, "10.1.2.3")]

        result = {
            "version": "1.0",
            "type": "rich",
            "html": "<div>Content Preview</div>",
        }
        end_content = json.dumps(result).encode("utf-8")

        channel = self.make_request(
            "GET",
            "preview_url?url=http://www.hulu.com/watch/12345",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        client = self.reactor.tcpClients[0][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            (
                b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
                b'Content-Type: application/json; charset="utf8"\r\n\r\n'
            )
            % (len(end_content),)
            + end_content
        )

        self.pump()

        # The {format} should have been turned into json.
        self.assertIn(b"/api/oembed.json", server.data)
        # A URL parameter of format=json should be provided.
        self.assertIn(b"format=json", server.data)

        self.assertEqual(channel.code, 200)
        body = channel.json_body
        self.assertEqual(
            body,
            {
                "og:url": "http://www.hulu.com/watch/12345",
                "og:description": "Content Preview",
            },
        )

    def test_oembed_autodiscovery(self):
        """
        Autodiscovery works by finding the link in the HTML response and then requesting an oEmbed URL.
        1. Request a preview of a URL which is not known to the oEmbed code.
        2. It returns HTML including a link to an oEmbed preview.
        3. The oEmbed preview is requested and returns a URL for an image.
        4. The image is requested for thumbnailing.
        """
        # This is a little cheesy in that we use the www subdomain (which isn't the
        # list of oEmbed patterns) to get "raw" HTML response.
        self.lookups["www.twitter.com"] = [(IPv4Address, "10.1.2.3")]
        self.lookups["publish.twitter.com"] = [(IPv4Address, "10.1.2.3")]
        self.lookups["cdn.twitter.com"] = [(IPv4Address, "10.1.2.3")]

        result = b"""
        <link rel="alternate" type="application/json+oembed"
            href="http://publish.twitter.com/oembed?url=http%3A%2F%2Fcdn.twitter.com%2Fmatrixdotorg%2Fstatus%2F12345&format=json"
            title="matrixdotorg" />
        """

        channel = self.make_request(
            "GET",
            "preview_url?url=http://www.twitter.com/matrixdotorg/status/12345",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        client = self.reactor.tcpClients[0][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            (
                b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
                b'Content-Type: text/html; charset="utf8"\r\n\r\n'
            )
            % (len(result),)
            + result
        )

        self.pump()

        # The oEmbed response.
        result2 = {
            "version": "1.0",
            "type": "photo",
            "url": "http://cdn.twitter.com/matrixdotorg",
        }
        oembed_content = json.dumps(result2).encode("utf-8")

        # Ensure a second request is made to the oEmbed URL.
        client = self.reactor.tcpClients[1][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            (
                b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
                b'Content-Type: application/json; charset="utf8"\r\n\r\n'
            )
            % (len(oembed_content),)
            + oembed_content
        )

        self.pump()

        # Ensure the URL is what was requested.
        self.assertIn(b"/oembed?", server.data)

        # Ensure a third request is made to the photo URL.
        client = self.reactor.tcpClients[2][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            (
                b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
                b"Content-Type: image/png\r\n\r\n"
            )
            % (len(SMALL_PNG),)
            + SMALL_PNG
        )

        self.pump()

        # Ensure the URL is what was requested.
        self.assertIn(b"/matrixdotorg", server.data)

        self.assertEqual(channel.code, 200)
        body = channel.json_body
        self.assertEqual(
            body["og:url"], "http://www.twitter.com/matrixdotorg/status/12345"
        )
        self.assertTrue(body["og:image"].startswith("mxc://"))
        self.assertEqual(body["og:image:height"], 1)
        self.assertEqual(body["og:image:width"], 1)
        self.assertEqual(body["og:image:type"], "image/png")

    def _download_image(self):
        """Downloads an image into the URL cache.
        Returns:
            A (host, media_id) tuple representing the MXC URI of the image.
        """
        self.lookups["cdn.twitter.com"] = [(IPv4Address, "10.1.2.3")]

        channel = self.make_request(
            "GET",
            "preview_url?url=http://cdn.twitter.com/matrixdotorg",
            shorthand=False,
            await_result=False,
        )
        self.pump()

        client = self.reactor.tcpClients[0][2].buildProtocol(None)
        server = AccumulatingProtocol()
        server.makeConnection(FakeTransport(client, self.reactor))
        client.makeConnection(FakeTransport(server, self.reactor))
        client.dataReceived(
            b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\nContent-Type: image/png\r\n\r\n"
            % (len(SMALL_PNG),)
            + SMALL_PNG
        )

        self.pump()
        self.assertEqual(channel.code, 200)
        body = channel.json_body
        mxc_uri = body["og:image"]
        host, _port, media_id = parse_and_validate_mxc_uri(mxc_uri)
        self.assertIsNone(_port)
        return host, media_id

    def test_storage_providers_exclude_files(self):
        """Test that files are not stored in or fetched from storage providers."""
        host, media_id = self._download_image()

        rel_file_path = self.preview_url.filepaths.url_cache_filepath_rel(media_id)
        media_store_path = os.path.join(self.media_store_path, rel_file_path)
        storage_provider_path = os.path.join(self.storage_path, rel_file_path)

        # Check storage
        self.assertTrue(os.path.isfile(media_store_path))
        self.assertFalse(
            os.path.isfile(storage_provider_path),
            "URL cache file was unexpectedly stored in a storage provider",
        )

        # Check fetching
        channel = self.make_request(
            "GET",
            f"download/{host}/{media_id}",
            shorthand=False,
            await_result=False,
        )
        self.pump()
        self.assertEqual(channel.code, 200)

        # Move cached file into the storage provider
        os.makedirs(os.path.dirname(storage_provider_path), exist_ok=True)
        os.rename(media_store_path, storage_provider_path)

        channel = self.make_request(
            "GET",
            f"download/{host}/{media_id}",
            shorthand=False,
            await_result=False,
        )
        self.pump()
        self.assertEqual(
            channel.code,
            404,
            "URL cache file was unexpectedly retrieved from a storage provider",
        )

    def test_storage_providers_exclude_thumbnails(self):
        """Test that thumbnails are not stored in or fetched from storage providers."""
        host, media_id = self._download_image()

        rel_thumbnail_path = (
            self.preview_url.filepaths.url_cache_thumbnail_directory_rel(media_id)
        )
        media_store_thumbnail_path = os.path.join(
            self.media_store_path, rel_thumbnail_path
        )
        storage_provider_thumbnail_path = os.path.join(
            self.storage_path, rel_thumbnail_path
        )

        # Check storage
        self.assertTrue(os.path.isdir(media_store_thumbnail_path))
        self.assertFalse(
            os.path.isdir(storage_provider_thumbnail_path),
            "URL cache thumbnails were unexpectedly stored in a storage provider",
        )

        # Check fetching
        channel = self.make_request(
            "GET",
            f"thumbnail/{host}/{media_id}?width=32&height=32&method=scale",
            shorthand=False,
            await_result=False,
        )
        self.pump()
        self.assertEqual(channel.code, 200)

        # Remove the original, otherwise thumbnails will regenerate
        rel_file_path = self.preview_url.filepaths.url_cache_filepath_rel(media_id)
        media_store_path = os.path.join(self.media_store_path, rel_file_path)
        os.remove(media_store_path)

        # Move cached thumbnails into the storage provider
        os.makedirs(os.path.dirname(storage_provider_thumbnail_path), exist_ok=True)
        os.rename(media_store_thumbnail_path, storage_provider_thumbnail_path)

        channel = self.make_request(
            "GET",
            f"thumbnail/{host}/{media_id}?width=32&height=32&method=scale",
            shorthand=False,
            await_result=False,
        )
        self.pump()
        self.assertEqual(
            channel.code,
            404,
            "URL cache thumbnail was unexpectedly retrieved from a storage provider",
        )

    def test_cache_expiry(self):
        """Test that URL cache files and thumbnails are cleaned up properly on expiry."""
        self.preview_url.clock = MockClock()

        _host, media_id = self._download_image()

        file_path = self.preview_url.filepaths.url_cache_filepath(media_id)
        file_dirs = self.preview_url.filepaths.url_cache_filepath_dirs_to_delete(
            media_id
        )
        thumbnail_dir = self.preview_url.filepaths.url_cache_thumbnail_directory(
            media_id
        )
        thumbnail_dirs = self.preview_url.filepaths.url_cache_thumbnail_dirs_to_delete(
            media_id
        )

        self.assertTrue(os.path.isfile(file_path))
        self.assertTrue(os.path.isdir(thumbnail_dir))

        self.preview_url.clock.advance_time_msec(IMAGE_CACHE_EXPIRY_MS + 1)
        self.get_success(self.preview_url._expire_url_cache_data())

        for path in [file_path] + file_dirs + [thumbnail_dir] + thumbnail_dirs:
            self.assertFalse(
                os.path.exists(path),
                f"{os.path.relpath(path, self.media_store_path)} was not deleted",
            )