German "Umlaute" and colon seem to be unusable in file sync from server to app

[Jan-NiklasB]

⚠️ Before posting ⚠️

• This is a bug, not a question or an enhancement.
• I've searched for similar issues and didn't find a duplicate.
• I've written a clear and descriptive title for this issue, not just "Bug" or "Crash".
• I agree to follow Nextcloud's Code of Conduct.

Steps to reproduce

Create a file named in a dir of your choice on the server:

Rettungsgasse ist kein Straßenname: Die Abenteuer eines Notfallsanitäters und Feuerwehrmanns.m4a

Try to sync with app -> error

Expected behaviour

File syncs as expected

Actual behaviour

Error syncing the file:
Invalid filename for local file

Android version

14

Device brand and model

Shift, Shiftphone 8.1

Stock or custom OS?

Custom (explain in "additional information")

Nextcloud android app version

3.35.1

Nextcloud server version

30.0.15

Using a reverse proxy?

Yes

Android logs

No response

Server error logs

Additional information

ROM: /e/OS Vers: 2.9-a14-20250323478433-community-otter

No folder/ file under path in logfile explanation

[joshtrichards]

: are problematic on Android. The client restricts naming using the same logic as the OS:

android/app/src/main/java/com/owncloud/android/utils/FileStorageUtils.java

Lines 138 to 157 in 59f6869

	/**
	* Checks whether the given character is valid in an extended file name.
	* <p>
	* Reference: <a href="https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/android/os/FileUtils.java;l=997">
	* android.os.FileUtils#isValidExtFilenameChar(char)
	* </a> from the Android Open Source Project.
	*
	* @param c the character to validate
	* @return true if the character is valid in a filename, false otherwise
	*/
	private static boolean isValidExtFilenameChar(char c) {
	if ((int) c <= 0x1F) {
	return false;
	}
	return switch (c) {
	case '"', '*', ':', '/', '<', '>', '?', '\\', '|', 0x7F -> false;
	default -> true;
	};
	}