Query rest-server configuration?

Getting Help
1

I have set up a rest-server and started it with:

rest-server --path /nfs/restic --append-only --private-repos --tls

Creating restic snapshots was successful:

tux@zoo:~: restic-snapshots 
RESTIC_REPOSITORY=rest:https://zoo.rus.uni-stuttgart.de:8000/test
repository 2ccd5e44 opened (version 2, compression level auto)
snapshots for (tags [_home_tux]):
ID        Time                 Host        Tags        Paths
----------------------------------------------------------------
e00ecd13  2024-05-08 14:36:44  zoo         _home_tux   /home/tux
36d9ee7c  2024-05-08 14:36:46  zoo         _home_tux   /home/tux
e3f704fa  2024-05-08 14:36:48  zoo         _home_tux   /home/tux
04693876  2024-05-08 14:37:01  zoo         _home_tux   /home/tux
336d5221  2024-05-08 14:38:59  zoo         _home_tux   /home/tux
8e476249  2024-05-08 14:39:06  zoo         _home_tux   /home/tux
----------------------------------------------------------------
6 snapshots

But when I try to forget or prune some of these snapshots I get endless error messages:

tux@zoo:~: restic forget --keep-last 4
RESTIC_REPOSITORY=rest:https://zoo.rus.uni-stuttgart.de:8000/test
repository 2ccd5e44 opened (version 2, compression level auto)
Applying Policy: keep 4 latest snapshots
keep 4 snapshots:
ID        Time                 Host        Tags        Reasons        Paths
-------------------------------------------------------------------------------
e3f704fa  2024-05-08 14:36:48  zoo         _home_tux   last snapshot  /home/tux
04693876  2024-05-08 14:37:01  zoo         _home_tux   last snapshot  /home/tux
336d5221  2024-05-08 14:38:59  zoo         _home_tux   last snapshot  /home/tux
8e476249  2024-05-08 14:39:06  zoo         _home_tux   last snapshot  /home/tux
-------------------------------------------------------------------------------
4 snapshots

remove 2 snapshots:
ID        Time                 Host        Tags        Paths
----------------------------------------------------------------
e00ecd13  2024-05-08 14:36:44  zoo         _home_tux   /home/tux
36d9ee7c  2024-05-08 14:36:46  zoo         _home_tux   /home/tux
----------------------------------------------------------------
2 snapshots

Remove(<snapshot/e00ecd13a3>) returned error, retrying after 364.800382ms: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/36d9ee7c59>) returned error, retrying after 617.058248ms: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/e00ecd13a3>) returned error, retrying after 1.011905766s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/36d9ee7c59>) returned error, retrying after 700.938105ms: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/36d9ee7c59>) returned error, retrying after 1.375621978s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/e00ecd13a3>) returned error, retrying after 743.633677ms: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/e00ecd13a3>) returned error, retrying after 2.333579491s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/36d9ee7c59>) returned error, retrying after 1.229276296s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/36d9ee7c59>) returned error, retrying after 1.989210274s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/e00ecd13a3>) returned error, retrying after 1.980155835s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/36d9ee7c59>) returned error, retrying after 2.749113488s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/e00ecd13a3>) returned error, retrying after 2.491468884s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/36d9ee7c59>) returned error, retrying after 5.921608135s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/e00ecd13a3>) returned error, retrying after 7.150741801s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/36d9ee7c59>) returned error, retrying after 9.009004469s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/e00ecd13a3>) returned error, retrying after 4.314839768s: blob not removed, server response: 403 Forbidden (403)
Remove(<snapshot/e00ecd13a3>) returned error, retrying after 10.136100619s: blob not removed, server response: 403 Forbidden (403)
  signal interrupt received, cleaning up
unable to remove <snapshot/36d9ee7c59> from the repository
unable to remove <snapshot/e00ecd13a3> from the repository
[0:22] 0.00%  0 / 2 files deleted
context canceled

I know deleting SHALL not be possible because the rest-server runs in append-only, but how does a client know this?
In my case I am the backup server admin and I know this, but others will not know it.

(How) can a restic client query the rest-server config, especially whether append-only mode is active?
Background: I want to write some restic scripts which will do automatic prune (if it is possible).

2

I’m not sure whether there is a way to query the mode but I suggest running the prune directly on the server itself against the folder containing the repo (e.g. restic -r /srv/backup ...). This way clients can append and the server prunes.

What I do is have a script run every day that forgets and prunes according to retention policy. Additionally I run a weekly script with an integrity check by reading a slice of the data in the repo (check --read-data-subset="x/y").

3

I have several restic repositories with different modes/configuration: rest-server, NFS and S3
I want to distribute restic wrapper scripts which do snapshots and auto-prune. The last one is only possible if the repository supports it, no append-only mode.
The client should check this and not hang in an error loop.