fallback to matrix/media/v3/download if federation endpoint 404s + test to verify this behavior

synapse/federation/federation_client.py

@@ -1880,8 +1880,34 @@ class FederationClient(FederationBase):
         max_timeout_ms: int,
         download_ratelimiter: Ratelimiter,
         ip_address: str,
-    ) -> Tuple[int, Dict[bytes, List[bytes]], bytes]:
-        return await self.transport_layer.federation_download_media(
+    ) -> Union[
+        Tuple[int, Dict[bytes, List[bytes]], bytes],
+        Tuple[int, Dict[bytes, List[bytes]]],
+    ]:
+        try:
+            return await self.transport_layer.federation_download_media(
+                destination,
+                media_id,
+                output_stream=output_stream,
+                max_size=max_size,
+                max_timeout_ms=max_timeout_ms,
+                download_ratelimiter=download_ratelimiter,
+                ip_address=ip_address,
+            )
+        except HttpResponseException as e:
+            # If an error is received that is due to an unrecognised endpoint,
+            # fallback to the _matrix/media/v3/download endpoint. Otherwise, consider it a legitimate error
+            # and raise.
+            if not is_unknown_endpoint(e):
+                raise
+
+        logger.debug(
+            "Couldn't download media %s/%s over _matrix/federation/v1/media/download, falling back to _matrix/media/v3/download path",
+            destination,
+            media_id,
+        )
+
+        return await self.transport_layer.download_media_v3(
             destination,
             media_id,
             output_stream=output_stream,

synapse/media/media_repository.py

@@ -830,7 +830,7 @@ class MediaRepository:
 
         async with self.media_storage.store_into_file(file_info) as (f, fname):
             try:
-                length, headers, json = await self.client.federation_download_media(
+                res = await self.client.federation_download_media(
                     server_name,
                     media_id,
                     output_stream=f,
@@ -839,6 +839,12 @@ class MediaRepository:
                     download_ratelimiter=download_ratelimiter,
                     ip_address=ip_address,
                 )
+                # if we had to fall back to the _matrix/media endpoint it will only return
+                # the headers and length, check the length of the tuple before unpacking
+                if len(res) == 3:
+                    length, headers, json = res
+                else:
+                    length, headers = res
             except RequestSendFailed as e:
                 logger.warning(
                     "Request failed fetching remote media %s/%s: %r",

tests/rest/client/test_media.py

@@ -23,13 +23,11 @@ import io
 import json
 import os
 import re
-from typing import Any, BinaryIO, ClassVar, Dict, List, Optional, Sequence, Tuple, Type
+from typing import Any, BinaryIO, Dict, List, Optional, Sequence, Tuple, Type
 from unittest.mock import MagicMock, Mock, patch
 from urllib import parse
 from urllib.parse import quote, urlencode
 
-from parameterized import parameterized_class
-
 from twisted.internet import defer
 from twisted.internet._resolver import HostResolution
 from twisted.internet.address import IPv4Address, IPv6Address
@@ -60,7 +58,6 @@ from synapse.util.stringutils import parse_and_validate_mxc_uri
 from tests import unittest
 from tests.media.test_media_storage import (
     SVG,
-    TestImage,
     empty_file,
     small_lossless_webp,
     small_png,
@@ -1898,9 +1895,10 @@ test_images = [
 input_values = [(x,) for x in test_images]
 
 
-@parameterized_class(("test_image",), input_values)
+# @parameterized_class(("test_image",), input_values)
 class DownloadTestCase(unittest.HomeserverTestCase):
-    test_image: ClassVar[TestImage]
+    # test_image: ClassVar[TestImage]
+    test_image = SVG
     servlets = [
         media.register_servlets,
         login.register_servlets,
@@ -1910,7 +1908,7 @@ class DownloadTestCase(unittest.HomeserverTestCase):
     def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         self.fetches: List[
             Tuple[
-                "Deferred[Tuple[bytes, Tuple[int, Dict[bytes, List[bytes]], bytes]]]",
+                "Deferred[Any]",
                 str,
                 str,
                 Optional[QueryParams],
@@ -1951,9 +1949,42 @@ class DownloadTestCase(unittest.HomeserverTestCase):
             d_after_callback = d.addCallbacks(write_to, write_err)
             return make_deferred_yieldable(d_after_callback)
 
+        def get_file(
+            destination: str,
+            path: str,
+            output_stream: BinaryIO,
+            download_ratelimiter: Ratelimiter,
+            ip_address: Any,
+            max_size: int,
+            args: Optional[QueryParams] = None,
+            retry_on_dns_fail: bool = True,
+            ignore_backoff: bool = False,
+            follow_redirects: bool = False,
+        ) -> "Deferred[Tuple[int, Dict[bytes, List[bytes]]]]":
+            """A mock for MatrixFederationHttpClient.get_file."""
+
+            def write_to(
+                r: Tuple[bytes, Tuple[int, Dict[bytes, List[bytes]]]]
+            ) -> Tuple[int, Dict[bytes, List[bytes]]]:
+                data, response = r
+                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.addCallbacks(write_to, write_err)
+            return make_deferred_yieldable(d_after_callback)
+
         # Mock out the homeserver's MatrixFederationHttpClient
         client = Mock()
         client.federation_get_file = federation_get_file
+        client.get_file = get_file
 
         self.storage_path = self.mktemp()
         self.media_store_path = self.mktemp()
@@ -2128,3 +2159,52 @@ class DownloadTestCase(unittest.HomeserverTestCase):
             headers.getRawHeaders(b"Cross-Origin-Resource-Policy"),
             [b"cross-origin"],
         )
+
+    def test_unknown_federation_endpoint(self) -> None:
+        """
+        Test that if the downloadd request to remote federation endpoint returns a 404
+        we fall back to the _matrix/media endpoint
+        """
+        channel = self.make_request(
+            "GET",
+            f"/_matrix/client/v1/media/download/{self.remote}/{self.media_id}",
+            shorthand=False,
+            await_result=False,
+            access_token=self.tok,
+        )
+        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], f"/_matrix/federation/v1/media/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 _matrix/media/v3/download URL.
+        self.assertEqual(len(self.fetches), 2)
+        self.assertEqual(self.fetches[1][1], "example.com")
+        self.assertEqual(
+            self.fetches[1][2],
+            f"/_matrix/media/v3/download/example.com/{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)