fix: Make user removal more resilient

[susnux]

• Resolves: User data not deleted if User::delete failed #47900

Summary

Currently there is a problem if an exception is thrown in User::delete, because at that point the user is already removed from the backend, but not all data is deleted.

There is no way to recover from this state, as the user is gone no information is available anymore. This means the data is still available on the server but can not removed by any API anymore.

The solution here is to first set a flag and backup the user home, this can be used to recover failed user deletions in a way the delete can be re-tried.

Discussion

I am not 100% sure this is the best way, but as out API needs real user instances to delete user data, I think we need to go with the "FailedUsersBackend".
I tested this with injecting various exceptions in random places in the User::delete method and then let the background job cleanup the state. In my test cases this worked as expected.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[susnux]

@blizzz I think you got a point here, we need to cover the case where backend->deleteUser threw an exception.
(if it returned we are always in a defined state)

[blizzz]

Not tested, but looking ok

[come-nc]

I like the idea, not sure I like the fact that it runs daily.

[susnux]

I like the idea, not sure I like the fact that it runs daily.

It simply skips if there is nothing to do, otherwise it only does things in the maintenance window.

[susnux]

/backport to stable30

[susnux]

/backport to stable29

[susnux]

/backport to stable28

[come-nc]

I still disagree that this should run daily.
It should be a repair-step. We have ton of other repair steps or occ commands to fix problems, non of them run daily.

[susnux]

I still disagree that this should run daily.
It should be a repair-step. We have ton of other repair steps or occ commands to fix problems, non of them run daily.

But it is not expensive, yet it ensures that you are compliant with data protection laws as deleted users are really deleted.

[come-nc]

Ok, legal requirement is a good reason to run it daily.

[susnux]

/backport to stable30

[susnux]

/backport to stable29

[susnux]

/backport to stable28

[backportbot]

The backport to stable28 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable28
git pull origin stable28

# Create the new backport branch
git checkout -b backport/47896/stable28

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 16833aff d57a2dd4

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/47896/stable28

Error: Failed to create pull request: Validation Failed: {"resource":"PullRequest","code":"custom","message":"A pull request already exists for nextcloud:backport/47896/stable28."}

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[backportbot]

The backport to stable29 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable29
git pull origin stable29

# Create the new backport branch
git checkout -b backport/47896/stable29

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 16833aff d57a2dd4

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/47896/stable29

Error: Failed to create pull request: Validation Failed: {"resource":"PullRequest","code":"custom","message":"A pull request already exists for nextcloud:backport/47896/stable29."}

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[backportbot]

The backport to stable30 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable30
git pull origin stable30

# Create the new backport branch
git checkout -b backport/47896/stable30

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 16833aff d57a2dd4

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/47896/stable30

Error: Failed to create pull request: Validation Failed: {"resource":"PullRequest","code":"custom","message":"A pull request already exists for nextcloud:backport/47896/stable30."}

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.