Cfrtjryk

I am trying to install a custom thumbnailer for nautilus on Debian testing (Buster) for quite some time now and I can not find an explanation why it doesn't work. Here is a minimal example of what I've been doing:

My first step was to create a file "plaintext.thumbnailer" in the ~/.local/share/thumbnailers/ folder:

[Thumbnailer Entry]

TryExec=$HOME/thumbnailer

Exec=$HOME/thumbnailer %i %o %s

MimeType=text/plain;

The thumbnailer is executable and located in my home folder.
Afterwards I deleted all cached thumbnails with rm -r ~/.cache/thumbnails and killed nautilus with killall nautilus.

However, when I restart Nautilus and open a folder that contains plain text files, I can see that Nautilus tries to generate thumbnails, but fails. Afterwards, the folder ~/.cache/thumbnails/fail/gnome-thumbnail-factory contains exactly as many items as nautilus tried to generate thumbnails for.

The thumbnailer itself is never executed, although Nautilus does find the thumbnailer entry "plaintext.thumbnailer". (If it's deleted, Nautilus doesn't try to generate thumbnails for text/plain anymore, i.e. it does not create any files in ~/.cache/thumbnails/fail/)

For the sake of completeness I'll also provide the source code of the thumbnailer:

#include <string>



#include <cstdlib>



using namespace std;



int main ( int argc, char **argv ) {

  string cmd ( "cp test.png " );

  cmd += argv[2];



  system ( cmd.c_str ( ) );



  return 0;

}

Update: I compiled test-desktop-thumbnail.c from the gnome-desktop git repository https://github.com/GNOME/gnome-desktop and used the executable to test thumbnail generation for plain text files, which worked perfectly fine. So I'm guessing there is something wrong with Nautilus.

Update #2: After digging into the nautilus source code I spotted that the call to gnome_desktop_thumbnail_factory_generate_thumbnail ( ... ) in nautilus-thumbnails.c fails for plain text files, although it is called with the very same arguments as in test-desktop-thumbnail.c. As a workaround I replaced it with a system call invoking the compiled test-desktop-thumbnail.c, which is ugly, but does the job.

But I still have no explanation for the behavior of the function gnome_desktop_thumbnail_factory_generate_thumbnail ( ... ), so it would be great if someone could shed some light on this.