Support MSC3916 by adding a federation /download endpoint

synapse/federation/transport/server/_base.py

@@ -356,13 +356,29 @@ async def new_func(
                                     "request"
                                 )
                                 return None
+                            if (
+                                func.__self__.__class__.__name__  # type: ignore
+                                == "FederationUnstableMediaDownloadServlet"
+                            ):
+                                response = await func(
+                                    origin, content, request, *args, **kwargs
+                                )
+                            else:
+                                response = await func(
+                                    origin, content, request.args, *args, **kwargs
+                                )
+                    else:
+                        if (
+                            func.__self__.__class__.__name__  # type: ignore
+                            == "FederationUnstableMediaDownloadServlet"
+                        ):
+                            response = await func(
+                                origin, content, request, *args, **kwargs
+                            )
+                        else:
                             response = await func(
                                 origin, content, request.args, *args, **kwargs
                             )
-                    else:
-                        response = await func(
-                            origin, content, request.args, *args, **kwargs
-                        )
             finally:
                 # if we used the origin's context as the parent, add a new span using
                 # the servlet span as a parent, so that we have a link

synapse/federation/transport/server/federation.py

@@ -44,10 +44,13 @@
 )
 from synapse.http.servlet import (
     parse_boolean_from_args,
+    parse_integer,
     parse_integer_from_args,
     parse_string_from_args,
     parse_strings_from_args,
 )
+from synapse.http.site import SynapseRequest
+from synapse.media._base import DEFAULT_MAX_TIMEOUT_MS, MAXIMUM_ALLOWED_MAX_TIMEOUT_MS
 from synapse.types import JsonDict
 from synapse.util import SYNAPSE_VERSION
 from synapse.util.ratelimitutils import FederationRateLimiter
@@ -787,6 +790,44 @@ async def on_POST(
         return 200, {"account_statuses": statuses, "failures": failures}
 
 
+class FederationUnstableMediaDownloadServlet(BaseFederationServerServlet):
+    """
+    Implementation of new federation media `/download` endpoint outlined in MSC3916. Returns
+    a multipart/form-data response consisting of a JSON object and the requested media
+    item. This endpoint only returns local media.
+    """
+
+    PATH = "/media/download/(?P<server_name>[^/]*)/(?P<media_id>[^/]*)"
+    PREFIX = FEDERATION_UNSTABLE_PREFIX + "/org.matrix.msc3916"
+    RATELIMIT = True
+
+    def __init__(
+        self,
+        hs: "HomeServer",
+        ratelimiter: FederationRateLimiter,
+        authenticator: Authenticator,
+        server_name: str,
+    ):
+        super().__init__(hs, authenticator, ratelimiter, server_name)
+        self.media_repo = self.hs.get_media_repository()
+
+    async def on_GET(
+        self,
+        origin: Optional[str],
+        content: Literal[None],
+        request: SynapseRequest,
+        server_name: str,
+        media_id: str,
+    ) -> None:
+        max_timeout_ms = parse_integer(
+            request, "timeout_ms", default=DEFAULT_MAX_TIMEOUT_MS
+        )
+        max_timeout_ms = min(max_timeout_ms, MAXIMUM_ALLOWED_MAX_TIMEOUT_MS)
+        await self.media_repo.get_local_media(
+            request, media_id, None, max_timeout_ms, federation=True
+        )
+
+
 FEDERATION_SERVLET_CLASSES: Tuple[Type[BaseFederationServlet], ...] = (
     FederationSendServlet,
     FederationEventServlet,
@@ -818,4 +859,5 @@ async def on_POST(
     FederationV1SendKnockServlet,
     FederationMakeKnockServlet,
     FederationAccountStatusServlet,
+    FederationUnstableMediaDownloadServlet,
 )