500 error "min() arg is an empty sequence" when requesting a thumbnail

[darnir]

Description

Looking at the logfile for my homeserver, I see the the following error message pop up fairly frequently:

2019-05-01 14:12:25,452 - synapse.http.server - 112 - ERROR - GET-38086 - Failed handle request via 'ThumbnailResource': <XForwardedForRequest at 0x7fe3dd9286a0 method='GET' uri='/_matrix/media/v1/thumbnail/raim.ist/KthgQjZpYLHEVOIzwvTjkXPx?width=150&height=150&method=scale' clientproto='HTTP/1.0' site=8008>
Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/twisted/internet/defer.py", line 1418, in _inlineCallbacks
    result = g.send(result)
  File "/usr/lib/python3.6/site-packages/synapse/storage/_base.py", line 460, in runWithConnection
    defer.returnValue(result)
  File "/usr/lib/python3.6/site-packages/twisted/internet/defer.py", line 1362, in returnValue
    raise _DefGen_Return(val)
twisted.internet.defer._DefGen_Return: [{'thumbnail_width': 10, 'thumbnail_height': 10, 'thumbnail_method': 'crop', 'thumbnail_type': 'image/jpeg', 'thumbnail_length': 715, 'filesystem_id': 'ZsQNhbXXFdIhkmfWZvdvlAww'}]

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/twisted/internet/defer.py", line 1418, in _inlineCallbacks
    result = g.send(result)
  File "/usr/lib/python3.6/site-packages/synapse/storage/_base.py", line 418, in runInteraction
    defer.returnValue(result)
  File "/usr/lib/python3.6/site-packages/twisted/internet/defer.py", line 1362, in returnValue
    raise _DefGen_Return(val)
twisted.internet.defer._DefGen_Return: [{'thumbnail_width': 10, 'thumbnail_height': 10, 'thumbnail_method': 'crop', 'thumbnail_type': 'image/jpeg', 'thumbnail_length': 715, 'filesystem_id': 'ZsQNhbXXFdIhkmfWZvdvlAww'}]

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/synapse/http/server.py", line 81, in wrapped_request_handler
    yield h(self, request)
  File "/usr/lib/python3.6/site-packages/twisted/internet/defer.py", line 1416, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/usr/lib/python3.6/site-packages/twisted/python/failure.py", line 491, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "/usr/lib/python3.6/site-packages/synapse/rest/media/v1/thumbnail_resource.py", line 83, in _async_render_GET
    width, height, method, m_type
  File "/usr/lib/python3.6/site-packages/twisted/internet/defer.py", line 1418, in _inlineCallbacks
    result = g.send(result)
  File "/usr/lib/python3.6/site-packages/synapse/rest/media/v1/thumbnail_resource.py", line 244, in _respond_remote_thumbnail
    width, height, method, m_type, thumbnail_infos
  File "/usr/lib/python3.6/site-packages/synapse/rest/media/v1/thumbnail_resource.py", line 317, in _select_thumbnail
    return min(info_list2)[-1]
ValueError: min() arg is an empty sequence

There are 10s of such messages every day.

Steps to reproduce

I don't currently know what action can cause this error.

Version information

• Homeserver: My own HS

If not matrix.org:

• Version: 0.99.3

• Install method: pip3

• Platform:

Running inside a Alpine Linux LXC container on a Arch Linux host

[darnir]

Any suggestions / hints on why I'm seeing this and what can be done about it?

[darnir]

Anything at all? At the very least an acknowledgement of the issue would be nice.

If there's more info required, please let me know

[richvdh]

an acknowledgement of the issue would be nice.

sorry, not sure what I can say. Looks like an error. don't know what causes it, other than (obviously) it's related to thumbnails.

[richvdh]

possibly a dup of #3183

[darnir]

I don't think so. I still see such errors in my logs. I'm happy to help in any way I can to debug this.

[richvdh]

possibly a dup of #3183

this was the wrong link. I think I meant #3763. Or possibly #3813? However, I don't think it is really a dup of either of those. The root cause seems to be that a scaled thumbnail has been requested, but no scaled thumbnail has been generated for that image.

[FlyveHest]

I have just installed a Synapse server from the latest docker image (matrixdotorg/synapse:latest), and I am experiencing the same thing.

Feb 1 20:55:50 server docker/synapse[1746]: 2021-02-01 20:55:50,974 - synapse.http.server - 79 - ERROR - GET-13559 - Failed handle request via 'ThumbnailResource': <XForwardedForRequest at 0x7f309cfbeac0 method='GET' uri='/_matrix/media/r0/thumbnail/server.name/RdKqjaYyUAbouqMHCeVCbese?width=16&height=16&method=crop' clientproto='HTTP/1.1' site='8008'>
Feb 1 20:55:50 server docker/synapse[1746]: Traceback (most recent call last):
Feb 1 20:55:50 server docker/synapse[1746]: File "/usr/local/lib/python3.8/site-packages/synapse/http/server.py", line 224, in _async_render_wrapper
Feb 1 20:55:50 server docker/synapse[1746]: callback_return = await self._async_render(request)
Feb 1 20:55:50 server docker/synapse[1746]: File "/usr/local/lib/python3.8/site-packages/synapse/http/server.py", line 252, in _async_render
Feb 1 20:55:50 server docker/synapse[1746]: callback_return = await raw_callback_return
Feb 1 20:55:50 server docker/synapse[1746]: File "/usr/local/lib/python3.8/site-packages/synapse/rest/media/v1/thumbnail_resource.py", line 74, in _async_render_GET
Feb 1 20:55:50 server docker/synapse[1746]: await self._respond_local_thumbnail(
Feb 1 20:55:50 server docker/synapse[1746]: File "/usr/local/lib/python3.8/site-packages/synapse/rest/media/v1/thumbnail_resource.py", line 111, in _respond_local_thumbnail
Feb 1 20:55:50 server docker/synapse[1746]: thumbnail_info = self._select_thumbnail(
Feb 1 20:55:50 server docker/synapse[1746]: File "/usr/local/lib/python3.8/site-packages/synapse/rest/media/v1/thumbnail_resource.py", line 352, in _select_thumbnail
Feb 1 20:55:50 server docker/synapse[1746]: return min(crop_info_list2)[-1]
Feb 1 20:55:50 server docker/synapse[1746]: ValueError: min() arg is an empty sequence

[clokep]

This should be fixed by #9163 in Synapse v1.27.0. Forgot to link the issues.