MIME-type detector cannot detect double-extensions like .tar.gz by path.

[rotdrop]

Looking at the code here

server/lib/private/Files/Type/Detection.php

Line 210 in cc83222

$extension = strrchr($fileName, '.');

it appears that the current implementation of the IMimeTypeDetector is not able to map double extensions like .tar.gz etc.

Please note that such extension are even part of the core distribution in resources/config/mimetypemapping.dist.json.

I stumbled over this while trying to register .tar.xz which is not part of the core distribution. The mime is registered successfully, and running

occ maintenance:mimetype:update-db

successfully updates the mimetype table and also corrects existing entries in the filecache table, but when one uploades a new file with that extension it is not recognized.

[rotdrop]

Closing as composite extension generally do not seem to have a mime-type and there still no official mime-type for the -- in Unix systems still common -- tar + compression files.

So although the distributed resources/config/mimetypemapping.dist.json lists composite extension, they are really not used in Nextcloud. I suppose it is somehow instructive to keep the unsupported composite extension for illustration purposes.