Do not error when thumbnailing invalid files

synapse/rest/media/v1/_base.py

@@ -21,6 +21,7 @@
 
 from twisted.internet.interfaces import IConsumer
 from twisted.protocols.basic import FileSender
+from twisted.web.server import Request
 
 from synapse.api.errors import Codes, SynapseError, cs_error
 from synapse.http.server import finish_request, respond_with_json
@@ -69,13 +70,30 @@ def parse_media_id(request):
         )
 
 
-def respond_404(request):
-    respond_with_json(
-        request,
-        404,
-        cs_error("Not found %r" % (request.postpath,), code=Codes.NOT_FOUND),
-        send_cors=True,
-    )
+def respond_404(request: Request):
+    respond_with_code(request, 404)
+
+
+def respond_with_code(request: Request, code: int):
+    """
+    Sends an empty response with a status code.
+
+    Args:
+        request: The http request to respond to.
+        code: The HTTP response code.
+    """
+    # could alternatively use request.notifyFinish() and flip a flag when
+    # the Deferred fires, but since the flag is RIGHT THERE it seems like
+    # a waste.
+    if request._disconnected:
+        logger.warning(
+            "Not sending response to request %s, already disconnected.", request
+        )
+        return
+
+    request.setResponseCode(code)
+    request.setHeader(b"Content-Length", b"0")
+    finish_request(request)
 
 
 async def respond_with_file(

tests/rest/media/v1/test_media_storage.py

@@ -348,3 +348,4 @@ def _test_thumbnail(self, method, expected_body, expected_found):
         else:
             # A 404 with no body.
             self.assertEqual(channel.code, 404)
+            self.assertNotIn("body", channel.result)