Traceback when fetching remote media

[moritzdietz]

Description

When I was watching the homeserver.log file I noticed the following lines going by.

2021-07-05 22:56:01,678 - synapse.http.server - 93 - ERROR - GET-114720 - Failed handle request via 'ThumbnailResource': <XForwardedForRequest at 0x7f74e7313400 method='GET' uri='/_matrix/media/r0/thumbnail/matrix.org/dOhWUOiqfTEPQASnYCLKLINu?width=800&height=600&method=scale' clientproto='HTTP/1.1' site='8008'>
Traceback (most recent call last):
  File "/opt/venvs/matrix-synapse/lib/python3.8/site-packages/synapse/http/server.py", line 258, in _async_render_wrapper
    callback_return = await self._async_render(request)
  File "/opt/venvs/matrix-synapse/lib/python3.8/site-packages/synapse/http/server.py", line 286, in _async_render
    callback_return = await raw_callback_return
  File "/opt/venvs/matrix-synapse/lib/python3.8/site-packages/synapse/rest/media/v1/thumbnail_resource.py", line 83, in _async_render_GET
    await self._respond_remote_thumbnail(
  File "/opt/venvs/matrix-synapse/lib/python3.8/site-packages/synapse/rest/media/v1/thumbnail_resource.py", line 265, in _respond_remote_thumbnail
    await self._select_and_respond_with_thumbnail(
  File "/opt/venvs/matrix-synapse/lib/python3.8/site-packages/synapse/rest/media/v1/thumbnail_resource.py", line 306, in _select_and_respond_with_thumbnail
    file_info = self._select_thumbnail(
  File "/opt/venvs/matrix-synapse/lib/python3.8/site-packages/synapse/rest/media/v1/thumbnail_resource.py", line 481, in _select_thumbnail
    thumbnail_info = min(info_list)[-1]
TypeError: '<' not supported between instances of 'dict' and 'dict'

I couldn't find an open or closed issue regarding this error so I thought I'd open an issue for it.

Steps to reproduce

I can reproduce it with curl

curl "https://matrix.moritzdietz.com/_matrix/media/r0/thumbnail/matrix.org/dOhWUOiqfTEPQASnYCLKLINu?width=800&height=600&method=scale"

which results in the error above.
I can fetch the media just fine via matrix.org:

curl -L "https://matrix-federation.matrix.org/_matrix/media/r0/thumbnail/matrix.org/dOhWUOiqfTEPQASnYCLKLINu?width=800&height=600&method=scale" -o somemedia.png

Version information

• Homeserver: matrix.moritzdietz.com

If not matrix.org:

• Version: 1.37.1

• Install method: package manager

• Platform: Ubuntu 20.04 Server

I have dynamic_thumbnails set to false (as it's the default).

[erikjohnston]

What is your thumbnail_sizes config? I think you might hit this if it has duplicate values in it?

[moritzdietz]

I checked my yaml file and in neither the one shipped with my package manager nor the drop in yaml file in .conf.d/ has an activated yaml hash for that configuration.
Meaning: everything is commented out which controls the setting you mentioned.

My reasoning was that there must be some default and I can leave it like it is unless I really need to change or adapt it.

[erikjohnston]

The issue is here:

synapse/synapse/rest/media/v1/thumbnail_resource.py

Line 481 in 4b965c8

thumbnail_info = min(info_list)[-1]

, info_list is a list of tuples, where the last entry is a dict. I think what is happening is we're getting entries in there where all the numbers match, and so it tries and compares by the last entry in the tuple, which then fails. The fix would be to either a) deduplicate the list before sorting or b) using the key param to min to make the comparisons ignore the dict part.