If you don't have write access to a file on your Computer, fs.isReadOnly should return false.

What exactly you have in mind when you say - no write access?

chmod u-w Filename

@Wojbie What he means is when a file is marked as read-only for the current user i.e. the user cannot write to the file.

Are we speaking about single player setup then? I would find it weird for there to be file not belonging to server running server user.

Anyhow now that exact problem has been explained I agree. This is rather weird edge case but is should be fixable.

@Wilma456 I believe you mean true -- that's what fs.isReadOnly returns for read-only files (no write access)

CC (like Minecraft itself), relies on you having write access to your save directory. much more than this method would break if that were not the case!