Support MSC3916 by adding unstable media endpoints to `_matrix/client` (#17213)

[MSC3916](https://github.com/matrix-org/matrix-spec-proposals/blob/rav/authentication-for-media/proposals/3916-authentication-for-media.md)
adds new media endpoints under `_matrix/client`. This PR adds the
`/preview_url`, `/config`, and `/thumbnail` endpoints. `/download` will
be added in a follow-up PR once the work for the federation `/download`
endpoint is complete (see
https://github.com/element-hq/synapse/pull/17172).

Should be reviewable commit-by-commit.

2 files changed, 1689 insertions, 81 deletions

diff --git a/tests/media/test_media_storage.py b/tests/media/test_media_storage.py
index cae67e11c8..1bd51ceba2 100644
--- a/tests/media/test_media_storage.py
+++ b/tests/media/test_media_storage.py
@@ -18,6 +18,7 @@
 # [This file includes modifications made by New Vector Limited]
 #
 #
+import itertools
 import os
 import shutil
 import tempfile
@@ -46,11 +47,11 @@ from synapse.media._base import FileInfo, ThumbnailInfo
 from synapse.media.filepath import MediaFilePaths
 from synapse.media.media_storage import MediaStorage, ReadableFileWrapper
 from synapse.media.storage_provider import FileStorageProviderBackend
+from synapse.media.thumbnailer import ThumbnailProvider
 from synapse.module_api import ModuleApi
 from synapse.module_api.callbacks.spamchecker_callbacks import load_legacy_spam_checkers
 from synapse.rest import admin
-from synapse.rest.client import login
-from synapse.rest.media.thumbnail_resource import ThumbnailResource
+from synapse.rest.client import login, media
 from synapse.server import HomeServer
 from synapse.types import JsonDict, RoomAlias
 from synapse.util import Clock
@@ -153,68 +154,54 @@ class _TestImage:
     is_inline: bool = True
 
 
-@parameterized_class(
-    ("test_image",),
-    [
-        # small png
-        (
-            _TestImage(
-                SMALL_PNG,
-                b"image/png",
-                b".png",
-                unhexlify(
-                    b"89504e470d0a1a0a0000000d4948445200000020000000200806"
-                    b"000000737a7af40000001a49444154789cedc101010000008220"
-                    b"ffaf6e484001000000ef0610200001194334ee0000000049454e"
-                    b"44ae426082"
-                ),
-                unhexlify(
-                    b"89504e470d0a1a0a0000000d4948445200000001000000010806"
-                    b"0000001f15c4890000000d49444154789c636060606000000005"
-                    b"0001a5f645400000000049454e44ae426082"
-                ),
-            ),
-        ),
-        # small png with transparency.
-        (
-            _TestImage(
-                unhexlify(
-                    b"89504e470d0a1a0a0000000d49484452000000010000000101000"
-                    b"00000376ef9240000000274524e5300010194fdae0000000a4944"
-                    b"4154789c636800000082008177cd72b60000000049454e44ae426"
-                    b"082"
-                ),
-                b"image/png",
-                b".png",
-                # Note that we don't check the output since it varies across
-                # different versions of Pillow.
-            ),
-        ),
-        # small lossless webp
-        (
-            _TestImage(
-                unhexlify(
-                    b"524946461a000000574542505650384c0d0000002f0000001007"
-                    b"1011118888fe0700"
-                ),
-                b"image/webp",
-                b".webp",
-            ),
-        ),
-        # an empty file
-        (
-            _TestImage(
-                b"",
-                b"image/gif",
-                b".gif",
-                expected_found=False,
-                unable_to_thumbnail=True,
-            ),
-        ),
-        # An SVG.
-        (
-            _TestImage(
-                b"""<?xml version="1.0"?>
+small_png = _TestImage(
+    SMALL_PNG,
+    b"image/png",
+    b".png",
+    unhexlify(
+        b"89504e470d0a1a0a0000000d4948445200000020000000200806"
+        b"000000737a7af40000001a49444154789cedc101010000008220"
+        b"ffaf6e484001000000ef0610200001194334ee0000000049454e"
+        b"44ae426082"
+    ),
+    unhexlify(
+        b"89504e470d0a1a0a0000000d4948445200000001000000010806"
+        b"0000001f15c4890000000d49444154789c636060606000000005"
+        b"0001a5f645400000000049454e44ae426082"
+    ),
+)
+
+small_png_with_transparency = _TestImage(
+    unhexlify(
+        b"89504e470d0a1a0a0000000d49484452000000010000000101000"
+        b"00000376ef9240000000274524e5300010194fdae0000000a4944"
+        b"4154789c636800000082008177cd72b60000000049454e44ae426"
+        b"082"
+    ),
+    b"image/png",
+    b".png",
+    # Note that we don't check the output since it varies across
+    # different versions of Pillow.
+)
+
+small_lossless_webp = _TestImage(
+    unhexlify(
+        b"524946461a000000574542505650384c0d0000002f0000001007" b"1011118888fe0700"
+    ),
+    b"image/webp",
+    b".webp",
+)
+
+empty_file = _TestImage(
+    b"",
+    b"image/gif",
+    b".gif",
+    expected_found=False,
+    unable_to_thumbnail=True,
+)
+
+SVG = _TestImage(
+    b"""<?xml version="1.0"?>
 <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
   "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
 
@@ -223,19 +210,32 @@ class _TestImage:
   <circle cx="100" cy="100" r="50" stroke="black"
     stroke-width="5" fill="red" />
 </svg>""",
-                b"image/svg",
-                b".svg",
-                expected_found=False,
-                unable_to_thumbnail=True,
-                is_inline=False,
-            ),
-        ),
-    ],
+    b"image/svg",
+    b".svg",
+    expected_found=False,
+    unable_to_thumbnail=True,
+    is_inline=False,
 )
+test_images = [
+    small_png,
+    small_png_with_transparency,
+    small_lossless_webp,
+    empty_file,
+    SVG,
+]
+urls = [
+    "_matrix/media/r0/thumbnail",
+    "_matrix/client/unstable/org.matrix.msc3916/media/thumbnail",
+]
+
+
+@parameterized_class(("test_image", "url"), itertools.product(test_images, urls))
 class MediaRepoTests(unittest.HomeserverTestCase):
+    servlets = [media.register_servlets]
     test_image: ClassVar[_TestImage]
     hijack_auth = True
     user_id = "@test:user"
+    url: ClassVar[str]
 
     def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         self.fetches: List[
@@ -298,6 +298,7 @@ class MediaRepoTests(unittest.HomeserverTestCase):
             "config": {"directory": self.storage_path},
         }
         config["media_storage_providers"] = [provider_config]
+        config["experimental_features"] = {"msc3916_authenticated_media_enabled": True}
 
         hs = self.setup_test_homeserver(config=config, federation_http_client=client)
 
@@ -502,7 +503,7 @@ class MediaRepoTests(unittest.HomeserverTestCase):
         params = "?width=32&height=32&method=scale"
         channel = self.make_request(
             "GET",
-            f"/_matrix/media/v3/thumbnail/{self.media_id}{params}",
+            f"/{self.url}/{self.media_id}{params}",
             shorthand=False,
             await_result=False,
         )
@@ -530,7 +531,7 @@ class MediaRepoTests(unittest.HomeserverTestCase):
 
         channel = self.make_request(
             "GET",
-            f"/_matrix/media/v3/thumbnail/{self.media_id}{params}",
+            f"/{self.url}/{self.media_id}{params}",
             shorthand=False,
             await_result=False,
         )
@@ -566,12 +567,11 @@ class MediaRepoTests(unittest.HomeserverTestCase):
         params = "?width=32&height=32&method=" + method
         channel = self.make_request(
             "GET",
-            f"/_matrix/media/r0/thumbnail/{self.media_id}{params}",
+            f"/{self.url}/{self.media_id}{params}",
             shorthand=False,
             await_result=False,
         )
         self.pump()
-
         headers = {
             b"Content-Length": [b"%d" % (len(self.test_image.data))],
             b"Content-Type": [self.test_image.content_type],
@@ -580,7 +580,6 @@ class MediaRepoTests(unittest.HomeserverTestCase):
             (self.test_image.data, (len(self.test_image.data), headers))
         )
         self.pump()
-
         if expected_found:
             self.assertEqual(channel.code, 200)
 
@@ -603,7 +602,7 @@ class MediaRepoTests(unittest.HomeserverTestCase):
                 channel.json_body,
                 {
                     "errcode": "M_UNKNOWN",
-                    "error": "Cannot find any thumbnails for the requested media ('/_matrix/media/r0/thumbnail/example.com/12345'). This might mean the media is not a supported_media_format=(image/jpeg, image/jpg, image/webp, image/gif, image/png) or that thumbnailing failed for some other reason. (Dynamic thumbnails are disabled on this server.)",
+                    "error": f"Cannot find any thumbnails for the requested media ('/{self.url}/example.com/12345'). This might mean the media is not a supported_media_format=(image/jpeg, image/jpg, image/webp, image/gif, image/png) or that thumbnailing failed for some other reason. (Dynamic thumbnails are disabled on this server.)",
                 },
             )
         else:
@@ -613,7 +612,7 @@ class MediaRepoTests(unittest.HomeserverTestCase):
                 channel.json_body,
                 {
                     "errcode": "M_NOT_FOUND",
-                    "error": "Not found '/_matrix/media/r0/thumbnail/example.com/12345'",
+                    "error": f"Not found '/{self.url}/example.com/12345'",
                 },
             )
 
@@ -625,12 +624,12 @@ class MediaRepoTests(unittest.HomeserverTestCase):
 
         content_type = self.test_image.content_type.decode()
         media_repo = self.hs.get_media_repository()
-        thumbnail_resouce = ThumbnailResource(
+        thumbnail_provider = ThumbnailProvider(
             self.hs, media_repo, media_repo.media_storage
         )
 
         self.assertIsNotNone(
-            thumbnail_resouce._select_thumbnail(
+            thumbnail_provider._select_thumbnail(
                 desired_width=desired_size,
                 desired_height=desired_size,
                 desired_method=method,
diff --git a/tests/rest/client/test_media.py b/tests/rest/client/test_media.py
new file mode 100644
index 0000000000..600cbf8963
--- /dev/null
+++ b/tests/rest/client/test_media.py
@@ -0,0 +1,1609 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright 2022 The Matrix.org Foundation C.I.C.
+# Copyright (C) 2024 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+# Originally licensed under the Apache License, Version 2.0:
+# <http://www.apache.org/licenses/LICENSE-2.0>.
+#
+# [This file includes modifications made by New Vector Limited]
+#
+#
+import base64
+import json
+import os
+import re
+from typing import Any, Dict, Optional, Sequence, Tuple, Type
+from urllib.parse import quote, urlencode
+
+from twisted.internet._resolver import HostResolution
+from twisted.internet.address import IPv4Address, IPv6Address
+from twisted.internet.error import DNSLookupError
+from twisted.internet.interfaces import IAddress, IResolutionReceiver
+from twisted.test.proto_helpers import AccumulatingProtocol, MemoryReactor
+from twisted.web.resource import Resource
+
+from synapse.config.oembed import OEmbedEndpointConfig
+from synapse.media._base import FileInfo
+from synapse.media.url_previewer import IMAGE_CACHE_EXPIRY_MS
+from synapse.rest import admin
+from synapse.rest.client import login, media
+from synapse.server import HomeServer
+from synapse.types import JsonDict
+from synapse.util import Clock
+from synapse.util.stringutils import parse_and_validate_mxc_uri
+
+from tests import unittest
+from tests.server import FakeTransport, ThreadedMemoryReactorClock
+from tests.test_utils import SMALL_PNG
+from tests.unittest import override_config
+
+try:
+    import lxml
+except ImportError:
+    lxml = None  # type: ignore[assignment]
+
+
+class UnstableMediaDomainBlockingTests(unittest.HomeserverTestCase):
+    remote_media_id = "doesnotmatter"
+    remote_server_name = "evil.com"
+    servlets = [
+        media.register_servlets,
+        admin.register_servlets,
+        login.register_servlets,
+    ]
+
+    def make_homeserver(
+        self, reactor: ThreadedMemoryReactorClock, clock: Clock
+    ) -> HomeServer:
+        config = self.default_config()
+
+        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.media.storage_provider.FileStorageProviderBackend",
+            "store_local": True,
+            "store_synchronous": False,
+            "store_remote": True,
+            "config": {"directory": self.storage_path},
+        }
+
+        config["media_storage_providers"] = [provider_config]
+
+        return self.setup_test_homeserver(config=config)
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.store = hs.get_datastores().main
+
+        # Inject a piece of media. We'll use this to ensure we're returning a sane
+        # response when we're not supposed to block it, distinguishing a media block
+        # from a regular 404.
+        file_id = "abcdefg12345"
+        file_info = FileInfo(server_name=self.remote_server_name, file_id=file_id)
+        with hs.get_media_repository().media_storage.store_into_file(file_info) as (
+            f,
+            fname,
+            finish,
+        ):
+            f.write(SMALL_PNG)
+            self.get_success(finish())
+
+        self.get_success(
+            self.store.store_cached_remote_media(
+                origin=self.remote_server_name,
+                media_id=self.remote_media_id,
+                media_type="image/png",
+                media_length=1,
+                time_now_ms=clock.time_msec(),
+                upload_name="test.png",
+                filesystem_id=file_id,
+            )
+        )
+        self.register_user("user", "password")
+        self.tok = self.login("user", "password")
+
+    @override_config(
+        {
+            # Disable downloads from the domain we'll be trying to download from.
+            # Should result in a 404.
+            "prevent_media_downloads_from": ["evil.com"],
+            "dynamic_thumbnails": True,
+            "experimental_features": {"msc3916_authenticated_media_enabled": True},
+        }
+    )
+    def test_cannot_download_blocked_media_thumbnail(self) -> None:
+        """
+        Same test as test_cannot_download_blocked_media but for thumbnails.
+        """
+        response = self.make_request(
+            "GET",
+            f"/_matrix/client/unstable/org.matrix.msc3916/media/thumbnail/evil.com/{self.remote_media_id}?width=100&height=100",
+            shorthand=False,
+            content={"width": 100, "height": 100},
+            access_token=self.tok,
+        )
+        self.assertEqual(response.code, 404)
+
+    @override_config(
+        {
+            # Disable downloads from a domain we won't be requesting downloads from.
+            # This proves we haven't broken anything.
+            "prevent_media_downloads_from": ["not-listed.com"],
+            "dynamic_thumbnails": True,
+            "experimental_features": {"msc3916_authenticated_media_enabled": True},
+        }
+    )
+    def test_remote_media_thumbnail_normally_unblocked(self) -> None:
+        """
+        Same test as test_remote_media_normally_unblocked but for thumbnails.
+        """
+        response = self.make_request(
+            "GET",
+            f"/_matrix/client/unstable/org.matrix.msc3916/media/thumbnail/evil.com/{self.remote_media_id}?width=100&height=100",
+            shorthand=False,
+            access_token=self.tok,
+        )
+        self.assertEqual(response.code, 200)
+
+
+class UnstableURLPreviewTests(unittest.HomeserverTestCase):
+    if not lxml:
+        skip = "url preview feature requires lxml"
+
+    servlets = [media.register_servlets]
+    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: MemoryReactor, clock: Clock) -> HomeServer:
+        config = self.default_config()
+        config["experimental_features"] = {"msc3916_authenticated_media_enabled": True}
+        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_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.media.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: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.media_repo = hs.get_media_repository()
+        assert self.media_repo.url_previewer is not None
+        self.url_previewer = self.media_repo.url_previewer
+
+        self.lookups: Dict[str, Any] = {}
+
+        class Resolver:
+            def resolveHostName(
+                _self,
+                resolutionReceiver: IResolutionReceiver,
+                hostName: str,
+                portNumber: int = 0,
+                addressTypes: Optional[Sequence[Type[IAddress]]] = None,
+                transportSemantics: str = "TCP",
+            ) -> IResolutionReceiver:
+                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()  # type: ignore[assignment]
+
+    def create_resource_dict(self) -> Dict[str, Resource]:
+        """Create a resource tree for the test server
+
+        A resource tree is a mapping from path to twisted.web.resource.
+
+        The default implementation creates a JsonResource and calls each function in
+        `servlets` to register servlets against it.
+        """
+        resources = super().create_resource_dict()
+        resources["/_matrix/media"] = self.hs.get_media_repository_resource()
+        return resources
+
+    def _assert_small_png(self, json_body: JsonDict) -> None:
+        """Assert properties from the SMALL_PNG test image."""
+        self.assertTrue(json_body["og:image"].startswith("mxc://"))
+        self.assertEqual(json_body["og:image:height"], 1)
+        self.assertEqual(json_body["og:image:width"], 1)
+        self.assertEqual(json_body["og:image:type"], "image/png")
+        self.assertEqual(json_body["matrix:image:size"], 67)
+
+    def test_cache_returns_correct_type(self) -> None:
+        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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.url_previewer._cache)
+        self.url_previewer._cache.pop("http://matrix.org")
+        self.assertNotIn("http://matrix.org", self.url_previewer._cache)
+
+        # Check the database cache returns the correct response
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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) -> None:
+        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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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_video_rejected(self) -> None:
+        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
+
+        end_content = b"anything"
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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: video/mp4\r\n\r\n"
+            )
+            % (len(end_content))
+            + end_content
+        )
+
+        self.pump()
+        self.assertEqual(channel.code, 502)
+        self.assertEqual(
+            channel.json_body,
+            {
+                "errcode": "M_UNKNOWN",
+                "error": "Requested file's content type not allowed for this operation: video/mp4",
+            },
+        )
+
+    def test_audio_rejected(self) -> None:
+        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
+
+        end_content = b"anything"
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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: audio/aac\r\n\r\n"
+            )
+            % (len(end_content))
+            + end_content
+        )
+
+        self.pump()
+        self.assertEqual(channel.code, 502)
+        self.assertEqual(
+            channel.json_body,
+            {
+                "errcode": "M_UNKNOWN",
+                "error": "Requested file's content type not allowed for this operation: audio/aac",
+            },
+        )
+
+    def test_non_ascii_preview_content_type(self) -> None:
+        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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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) -> None:
+        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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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) -> None:
+        """
+        IP addresses can be previewed directly.
+        """
+        self.lookups["example.com"] = [(IPv4Address, "10.1.2.3")]
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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_blocked_ip_specific(self) -> None:
+        """
+        Blocked IP addresses, found via DNS, are not spidered.
+        """
+        self.lookups["example.com"] = [(IPv4Address, "192.168.1.1")]
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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_blocked_ip_range(self) -> None:
+        """
+        Blocked IP ranges, IPs found over DNS, are not spidered.
+        """
+        self.lookups["example.com"] = [(IPv4Address, "1.1.1.2")]
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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_blocked_ip_specific_direct(self) -> None:
+        """
+        Blocked IP addresses, accessed directly, are not spidered.
+        """
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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"},
+        )
+        self.assertEqual(channel.code, 403)
+
+    def test_blocked_ip_range_direct(self) -> None:
+        """
+        Blocked IP ranges, accessed directly, are not spidered.
+        """
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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"},
+        )
+
+    def test_blocked_ip_range_whitelisted_ip(self) -> None:
+        """
+        Blocked but then subsequently whitelisted IP addresses can be
+        spidered.
+        """
+        self.lookups["example.com"] = [(IPv4Address, "1.1.1.1")]
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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_blocked_ip_with_external_ip(self) -> None:
+        """
+        If a hostname resolves a blocked IP, even if there's a non-blocked 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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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_blocked_ipv6_specific(self) -> None:
+        """
+        Blocked 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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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_blocked_ipv6_range(self) -> None:
+        """
+        Blocked IP ranges, IPs found over DNS, are not spidered.
+        """
+        self.lookups["example.com"] = [(IPv6Address, "2001:800::1")]
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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) -> None:
+        """
+        OPTIONS returns the OPTIONS.
+        """
+        channel = self.make_request(
+            "OPTIONS",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/preview_url?url=http://example.com",
+            shorthand=False,
+        )
+        self.assertEqual(channel.code, 204)
+
+    def test_accept_language_config_option(self) -> None:
+        """
+        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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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_image(self) -> None:
+        """An image should be precached if mentioned in the HTML."""
+        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
+        self.lookups["cdn.matrix.org"] = [(IPv4Address, "10.1.2.4")]
+
+        result = (
+            b"""<html><body><img src="http://cdn.matrix.org/foo.png"></body></html>"""
+        )
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/preview_url?url=http://matrix.org",
+            shorthand=False,
+            await_result=False,
+        )
+        self.pump()
+
+        # Respond with the HTML.
+        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()
+
+        # Respond with the photo.
+        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()
+
+        # The image should be in the result.
+        self.assertEqual(channel.code, 200)
+        self._assert_small_png(channel.json_body)
+
+    def test_nonexistent_image(self) -> None:
+        """If the preview image doesn't exist, ensure some data is returned."""
+        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
+
+        result = (
+            b"""<html><body><img src="http://cdn.matrix.org/foo.jpg"></body></html>"""
+        )
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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(result),)
+            + result
+        )
+
+        self.pump()
+
+        # There should not be a second connection.
+        self.assertEqual(len(self.reactor.tcpClients), 1)
+
+        # The image should not be in the result.
+        self.assertEqual(channel.code, 200)
+        self.assertNotIn("og:image", channel.json_body)
+
+    @unittest.override_config(
+        {"url_preview_url_blacklist": [{"netloc": "cdn.matrix.org"}]}
+    )
+    def test_image_blocked(self) -> None:
+        """If the preview image doesn't exist, ensure some data is returned."""
+        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
+        self.lookups["cdn.matrix.org"] = [(IPv4Address, "10.1.2.4")]
+
+        result = (
+            b"""<html><body><img src="http://cdn.matrix.org/foo.jpg"></body></html>"""
+        )
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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(result),)
+            + result
+        )
+        self.pump()
+
+        # There should not be a second connection.
+        self.assertEqual(len(self.reactor.tcpClients), 1)
+
+        # The image should not be in the result.
+        self.assertEqual(channel.code, 200)
+        self.assertNotIn("og:image", channel.json_body)
+
+    def test_oembed_failure(self) -> None:
+        """If the autodiscovered oEmbed URL fails, ensure some data is returned."""
+        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
+
+        result = b"""
+        <title>oEmbed Autodiscovery Fail</title>
+        <link rel="alternate" type="application/json+oembed"
+            href="http://example.com/oembed?url=http%3A%2F%2Fmatrix.org&format=json"
+            title="matrixdotorg" />
+        """
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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(result),)
+            + result
+        )
+
+        self.pump()
+        self.assertEqual(channel.code, 200)
+
+        # The image should not be in the result.
+        self.assertEqual(channel.json_body["og:title"], "oEmbed Autodiscovery Fail")
+
+    def test_data_url(self) -> None:
+        """
+        Requesting to preview a data URL is not supported.
+        """
+        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
+
+        data = base64.b64encode(SMALL_PNG).decode()
+
+        query_params = urlencode(
+            {
+                "url": f'<html><head><img src="data:image/png;base64,{data}" /></head></html>'
+            }
+        )
+
+        channel = self.make_request(
+            "GET",
+            f"/_matrix/client/unstable/org.matrix.msc3916/media/preview_url?{query_params}",
+            shorthand=False,
+        )
+        self.pump()
+
+        self.assertEqual(channel.code, 500)
+
+    def test_inline_data_url(self) -> None:
+        """
+        An inline image (as a data URL) should be parsed properly.
+        """
+        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
+
+        data = base64.b64encode(SMALL_PNG)
+
+        end_content = (
+            b"<html><head>" b'<img src="data:image/png;base64,%s" />' b"</head></html>"
+        ) % (data,)
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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._assert_small_png(channel.json_body)
+
+    def test_oembed_photo(self) -> None:
+        """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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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._assert_small_png(body)
+
+    def test_oembed_rich(self) -> None:
+        """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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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()
+
+        # Double check that the proper host is being connected to. (Note that
+        # twitter.com can't be resolved so this is already implicitly checked.)
+        self.assertIn(b"\r\nHost: publish.twitter.com\r\n", server.data)
+
+        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) -> None:
+        """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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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",
+            },
+        )
+
+    @unittest.override_config(
+        {"url_preview_url_blacklist": [{"netloc": "publish.twitter.com"}]}
+    )
+    def test_oembed_blocked(self) -> None:
+        """The oEmbed URL should not be downloaded if the oEmbed URL is blocked."""
+        self.lookups["twitter.com"] = [(IPv4Address, "10.1.2.3")]
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/preview_url?url=http://twitter.com/matrixdotorg/status/12345",
+            shorthand=False,
+            await_result=False,
+        )
+        self.pump()
+        self.assertEqual(channel.code, 403, channel.result)
+
+    def test_oembed_autodiscovery(self) -> None:
+        """
+        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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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._assert_small_png(body)
+
+    @unittest.override_config(
+        {"url_preview_url_blacklist": [{"netloc": "publish.twitter.com"}]}
+    )
+    def test_oembed_autodiscovery_blocked(self) -> None:
+        """
+        If the discovered oEmbed URL is blocked, it should be discarded.
+        """
+        # 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, "10.1.2.4")]
+
+        result = b"""
+        <title>Test</title>
+        <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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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()
+
+        # Ensure there's no additional connections.
+        self.assertEqual(len(self.reactor.tcpClients), 1)
+
+        # Ensure the URL is what was requested.
+        self.assertIn(b"\r\nHost: www.twitter.com\r\n", server.data)
+
+        self.assertEqual(channel.code, 200)
+        body = channel.json_body
+        self.assertEqual(body["og:title"], "Test")
+        self.assertNotIn("og:image", body)
+
+    def _download_image(self) -> Tuple[str, str]:
+        """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",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/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) -> None:
+        """Test that files are not stored in or fetched from storage providers."""
+        host, media_id = self._download_image()
+
+        rel_file_path = self.media_repo.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"/_matrix/media/v3/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"/_matrix/media/v3/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) -> None:
+        """Test that thumbnails are not stored in or fetched from storage providers."""
+        host, media_id = self._download_image()
+
+        rel_thumbnail_path = (
+            self.media_repo.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"/_matrix/client/unstable/org.matrix.msc3916/media/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.media_repo.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"/_matrix/client/unstable/org.matrix.msc3916/media/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) -> None:
+        """Test that URL cache files and thumbnails are cleaned up properly on expiry."""
+        _host, media_id = self._download_image()
+
+        file_path = self.media_repo.filepaths.url_cache_filepath(media_id)
+        file_dirs = self.media_repo.filepaths.url_cache_filepath_dirs_to_delete(
+            media_id
+        )
+        thumbnail_dir = self.media_repo.filepaths.url_cache_thumbnail_directory(
+            media_id
+        )
+        thumbnail_dirs = self.media_repo.filepaths.url_cache_thumbnail_dirs_to_delete(
+            media_id
+        )
+
+        self.assertTrue(os.path.isfile(file_path))
+        self.assertTrue(os.path.isdir(thumbnail_dir))
+
+        self.reactor.advance(IMAGE_CACHE_EXPIRY_MS * 1000 + 1)
+        self.get_success(self.url_previewer._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",
+            )
+
+    @unittest.override_config({"url_preview_url_blacklist": [{"port": "*"}]})
+    def test_blocked_port(self) -> None:
+        """Tests that blocking URLs with a port makes previewing such URLs
+        fail with a 403 error and doesn't impact other previews.
+        """
+        self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
+
+        bad_url = quote("http://matrix.org:8888/foo")
+        good_url = quote("http://matrix.org/foo")
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/preview_url?url="
+            + bad_url,
+            shorthand=False,
+            await_result=False,
+        )
+        self.pump()
+        self.assertEqual(channel.code, 403, channel.result)
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/preview_url?url="
+            + good_url,
+            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)
+
+    @unittest.override_config(
+        {"url_preview_url_blacklist": [{"netloc": "example.com"}]}
+    )
+    def test_blocked_url(self) -> None:
+        """Tests that blocking URLs with a host makes previewing such URLs
+        fail with a 403 error.
+        """
+        self.lookups["example.com"] = [(IPv4Address, "10.1.2.3")]
+
+        bad_url = quote("http://example.com/foo")
+
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/preview_url?url="
+            + bad_url,
+            shorthand=False,
+            await_result=False,
+        )
+        self.pump()
+        self.assertEqual(channel.code, 403, channel.result)
+
+
+class UnstableMediaConfigTest(unittest.HomeserverTestCase):
+    servlets = [
+        media.register_servlets,
+        admin.register_servlets,
+        login.register_servlets,
+    ]
+
+    def make_homeserver(
+        self, reactor: ThreadedMemoryReactorClock, clock: Clock
+    ) -> HomeServer:
+        config = self.default_config()
+        config["experimental_features"] = {"msc3916_authenticated_media_enabled": True}
+
+        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.media.storage_provider.FileStorageProviderBackend",
+            "store_local": True,
+            "store_synchronous": False,
+            "store_remote": True,
+            "config": {"directory": self.storage_path},
+        }
+
+        config["media_storage_providers"] = [provider_config]
+
+        return self.setup_test_homeserver(config=config)
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.register_user("user", "password")
+        self.tok = self.login("user", "password")
+
+    def test_media_config(self) -> None:
+        channel = self.make_request(
+            "GET",
+            "/_matrix/client/unstable/org.matrix.msc3916/media/config",
+            shorthand=False,
+            access_token=self.tok,
+        )
+        self.assertEqual(channel.code, 200)
+        self.assertEqual(
+            channel.json_body["m.upload.size"], self.hs.config.media.max_upload_size
+        )