[Bug]: File/folder renaming on Mac (slash "/" to colon ":") -> Sync error on Windows

[Ninos]

⚠️ Before submitting, please verify the following: ⚠️

• [X] This is a bug, not a question or a configuration issue.
• [X] This issue is not already reported on Github (I've searched it).
• [X] Nextcloud Server and Desktop Client are up to date. See Server Maintenance and Release Schedule and Desktop Releases for supported versions.
• [X] I agree to follow Nextcloud's Code of Conduct

Bug description

Files/folders with slashes in name got replaced with :, but this is not compatible with Windows (I think folder only) -> sync error.

Steps to reproduce

1. On Mac create folder with / in name, e.g. abc/def
2. Wait for sync
3. Check sync on Windows device

Expected behavior

Replace / e.g. with -, _ or something like that instead of :.

Which files are affected by this bug

abc/def/example.file

Operating system

Mac OS

Which version of the operating system you are running.

Mac OS Monterey

Package

Official SNAP package

Nextcloud Server version

24.0.4

Nextcloud Desktop Client version

3.5.4

Is this bug present after an update or on a fresh install?

Fresh desktop client install

Are you using the Nextcloud Server Encryption module?

Encryption is Enabled

Are you using an external user-backend?

• [X] Default internal user-backend
• [ ] LDAP/ Active Directory
• [ ] SSO - SAML
• [ ] Other

Nextcloud Server logs

No response

Additional info

No response

[User65481]

That said we would love an option to block all incompatible characters and warn users that their files didn't got synced. Having multiple thousands clients results in specialists who try to use /*?|^ - which works fine on their system but just won't show up on some other devices (for obvious reasons).

While they technically work I also strongly dislike emojis in file/folder names.

[trickysyntax]

Bumping this. Running into big problems with S3 and external storage — slashes in filenames are being replaced with colons — which allows them to be seen in the NC web interface but not in macOS Finder.

Using dashes or underscores instead of colons would fix this issue.

[huntervcx]

Bump this, really annoying in enterprise File Access Control could have the basic option to block files uploaded containing a colon, and returning to the user an error messaging explaining this

[joshtrichards]

Current behavior:

• https://docs.nextcloud.com/server/stable/admin_manual/configuration_server/config_sample_php_parameters.html#blacklisted-files
• https://docs.nextcloud.com/desktop/3.13/architecture.html#ignored-files

Upcoming:

• 6965

• https://docs.nextcloud.com/server/latest/admin_manual/release_notes/upgrade_to_30.html#nextcloud-configuration

[skarekrow]

The upcoming behavior seems far too manual. I would prefer an ability for the server to map filenames for the clients that can't represent them. For example, my maildir directory on my machine is uploaded to my nextcloud for backup. My windows machines try to synchronize that, and bomb out. The upcoming behavior in #6965 would require me to manually rename hundreds of thousands of files.

I think a great option would be for nextcloud to allow colons (or any other character that's not supported by the client OS) to be mapped to - or _ automatically. Same with slashes in the filename. It should just be a toggle that replaces invalid characters in filenames with hyphens or underscores.