fix(storage): Unlink symlink instead of deleting target content and link

[fxprunayre]

Summary

Nextcloud allow following symlink (https://docs.nextcloud.com/server/latest/admin_manual/configuration_server/config_sample_php_parameters.html#localstorage-allowsymlinks) but removal of symlink remove files in the target of the symlink and fail to remove the link returning an error.

Using the following structure:

.
├── afolder
│   └── test.txt
├── alink -> afolder
└── welcome.txt

created with:

mkdir afolder
touch afolder/test.txt
ln -s afolder alink

Current

After deletion of alink symbolic link, the content of afolder is removed, the link also and an error is reported.

{
  "method":"DELETE",
  "url":"/remote.php/dav/files/admin/alink",
  "message":"rmdir(/data/dev/nextcloud/data/admin/files/alink): Not a directory at /data/dev/nextcloud/lib/private/Files/Storage/Local.php#128"
}

Results is:

.
├── afolder
└── welcome.txt

After

If the resource to be deleted is a link, unlink it (and preserve link target content).

.
├── afolder
│   └── test.txt
└── welcome.txt

Todo

Quite new to the Nextcloud codebase, any pointer to a test related to symlink is welcomed.

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)

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