Request & follow redirects for /media/v3/download (#16701)

Implement MSC3860 to follow redirects for federated media downloads.

Note that the Client-Server API doesn't support this (yet) since the media
repository in Synapse doesn't have a way of supporting redirects.

2 files changed, 59 insertions, 5 deletions

diff --git a/tests/media/test_media_storage.py b/tests/media/test_media_storage.py
index f262304c3d..f981d1c0d8 100644
--- a/tests/media/test_media_storage.py
+++ b/tests/media/test_media_storage.py
@@ -27,10 +27,11 @@ from typing_extensions import Literal
 
 from twisted.internet import defer
 from twisted.internet.defer import Deferred
+from twisted.python.failure import Failure
 from twisted.test.proto_helpers import MemoryReactor
 from twisted.web.resource import Resource
 
-from synapse.api.errors import Codes
+from synapse.api.errors import Codes, HttpResponseException
 from synapse.events import EventBase
 from synapse.http.types import QueryParams
 from synapse.logging.context import make_deferred_yieldable
@@ -247,6 +248,7 @@ class MediaRepoTests(unittest.HomeserverTestCase):
             retry_on_dns_fail: bool = True,
             max_size: Optional[int] = None,
             ignore_backoff: bool = False,
+            follow_redirects: bool = False,
         ) -> "Deferred[Tuple[int, Dict[bytes, List[bytes]]]]":
             """A mock for MatrixFederationHttpClient.get_file."""
 
@@ -257,10 +259,15 @@ class MediaRepoTests(unittest.HomeserverTestCase):
                 output_stream.write(data)
                 return response
 
+            def write_err(f: Failure) -> Failure:
+                f.trap(HttpResponseException)
+                output_stream.write(f.value.response)
+                return f
+
             d: Deferred[Tuple[bytes, Tuple[int, Dict[bytes, List[bytes]]]]] = Deferred()
             self.fetches.append((d, destination, path, args))
             # Note that this callback changes the value held by d.
-            d_after_callback = d.addCallback(write_to)
+            d_after_callback = d.addCallbacks(write_to, write_err)
             return make_deferred_yieldable(d_after_callback)
 
         # Mock out the homeserver's MatrixFederationHttpClient
@@ -316,10 +323,11 @@ class MediaRepoTests(unittest.HomeserverTestCase):
         self.assertEqual(len(self.fetches), 1)
         self.assertEqual(self.fetches[0][1], "example.com")
         self.assertEqual(
-            self.fetches[0][2], "/_matrix/media/r0/download/" + self.media_id
+            self.fetches[0][2], "/_matrix/media/v3/download/" + self.media_id
         )
         self.assertEqual(
-            self.fetches[0][3], {"allow_remote": "false", "timeout_ms": "20000"}
+            self.fetches[0][3],
+            {"allow_remote": "false", "timeout_ms": "20000", "allow_redirect": "true"},
         )
 
         headers = {
@@ -671,6 +679,52 @@ class MediaRepoTests(unittest.HomeserverTestCase):
             [b"cross-origin"],
         )
 
+    def test_unknown_v3_endpoint(self) -> None:
+        """
+        If the v3 endpoint fails, try the r0 one.
+        """
+        channel = self.make_request(
+            "GET",
+            f"/_matrix/media/v3/download/{self.media_id}",
+            shorthand=False,
+            await_result=False,
+        )
+        self.pump()
+
+        # We've made one fetch, to example.com, using the media URL, and asking
+        # the other server not to do a remote fetch
+        self.assertEqual(len(self.fetches), 1)
+        self.assertEqual(self.fetches[0][1], "example.com")
+        self.assertEqual(
+            self.fetches[0][2], "/_matrix/media/v3/download/" + self.media_id
+        )
+
+        # The result which says the endpoint is unknown.
+        unknown_endpoint = b'{"errcode":"M_UNRECOGNIZED","error":"Unknown request"}'
+        self.fetches[0][0].errback(
+            HttpResponseException(404, "NOT FOUND", unknown_endpoint)
+        )
+
+        self.pump()
+
+        # There should now be another request to the r0 URL.
+        self.assertEqual(len(self.fetches), 2)
+        self.assertEqual(self.fetches[1][1], "example.com")
+        self.assertEqual(
+            self.fetches[1][2], f"/_matrix/media/r0/download/{self.media_id}"
+        )
+
+        headers = {
+            b"Content-Length": [b"%d" % (len(self.test_image.data))],
+        }
+
+        self.fetches[1][0].callback(
+            (self.test_image.data, (len(self.test_image.data), headers))
+        )
+
+        self.pump()
+        self.assertEqual(channel.code, 200)
+
 
 class TestSpamCheckerLegacy:
     """A spam checker module that rejects all media that includes the bytes
diff --git a/tests/replication/test_multi_media_repo.py b/tests/replication/test_multi_media_repo.py
index 1e9994cc0b..9a7b675f54 100644
--- a/tests/replication/test_multi_media_repo.py
+++ b/tests/replication/test_multi_media_repo.py
@@ -133,7 +133,7 @@ class MediaRepoShardTestCase(BaseMultiWorkerStreamTestCase):
         self.assertEqual(request.method, b"GET")
         self.assertEqual(
             request.path,
-            f"/_matrix/media/r0/download/{target}/{media_id}".encode(),
+            f"/_matrix/media/v3/download/{target}/{media_id}".encode(),
         )
         self.assertEqual(
             request.requestHeaders.getRawHeaders(b"host"), [target.encode("utf-8")]