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mtp: Fix crashes on NULL StorageDescriptions

Niklas Hambüchen requested to merge nh2/gvfs:mtp-dont-return-null-storage-names into master

The MTP spec section 5.2.2.7 allows StorageDescription to be an empty string.

libmtp currently translates this to

char * StorageDescription = NULL

instead of "" in ptp_unpack_SI() via ptp_unpack_string(). (I'm not sure if it's good that it does that, to be followed up on separately. Edit: https://github.com/libmtp/libmtp/issues/67)

create_storage_name() until now returned g_strdup(storage->StorageDescription), which returns NULL if NULL is given, and thus get_storage_info() would eventually call

char *storage_name = NULL = create_storage_name(storage);
g_file_info_set_name (info, storage_name = NULL);
g_file_info_set_display_name (info, storage_name = NULL);

resulting in assertion failures in gvfsd:

g_file_info_set_name: assertion 'name != NULL' failed
g_file_info_set_display_name: assertion 'display_name != NULL' failed

as well as crashes in file managers like Thunar:

g_file_get_child: assertion 'name != NULL' failed

and warnings in Nautilus like:

Got GFileInfo with NULL name in mtp://Ricoh_Company__Ltd._RICOH_THETA_V_00165759/, ignoring. This shouldn't happen unless the gvfs backend is broken.

This commit fixes it by adding a contract to create_storage_name() that it will never represent empty strings as NULL.

I've tested this on top of 1.44.1 on NixOS 20.09; it fixes the crashes of all programs mentioned above.

This fix is sponsored by my company benaco.com, so that users of the Ricoh Theta V and Theta Z1 cameras can use MTP instead of PTP, thus avoiding that > 4 GiB video files will be silently cut off.

Edited by Niklas Hambüchen

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