there exists the function
g_file_measure_disk_usage (see documentation) to calculate the disc usage of a given GFile object. Unfortunately it turns out that this function does not work on remote directories, mounted via GIO. For example, when I am connected to an FTP directory, I get the following terminal error output:
g_file_measure_disk_usage failed: Operation not supported for the current backend.
What do I have to do to calculate the the remote size then? I would need it to show the user the time it would need to copy/move directories from a remote directory to the local directory. Is it only possible to implement a disc size calculation function from scratch? It would be great to have something provided by GIO.