How can I read a folder owned by root with Vala? - directory

Question

I'm trying to read the path /var/cache/apt/archives with the following permissions:
drwxr-xr-x 3 root root 90112 ago 2 14:36 archives
And I got the following error:
ERROR: Error opening directory '/var/cache/apt/archives/partial': Permission denied
Can somebody give me a hand with this?
The source code is the following:
using Gtk;
using GLib;
private int64[] get_folder_data (File file, string space = "", Cancellable? cancellable = null) throws Error
{
FileEnumerator enumerator = file.enumerate_children (
"standard::*",
FileQueryInfoFlags.NOFOLLOW_SYMLINKS,
cancellable);
int64 files = 0;
int64 size = 0;
int64[] data = new int64[2];
FileInfo info = null;
while (cancellable.is_cancelled () == false && ((info = enumerator.next_file (cancellable)) != null)) {
if (info.get_file_type () == FileType.DIRECTORY) {
File subdir = file.resolve_relative_path (info.get_name ());
get_folder_data (subdir, space + " ", cancellable);
} else {
files += 1;//Sum Files
size += info.get_size ();//Accumulates Size
}
}
if (cancellable.is_cancelled ()) {
throw new IOError.CANCELLED ("Operation was cancelled");
}
data[0] = files;
data[1] = size;
stdout.printf ("APT CACHE SIZE: %s\n", files.to_string());
stdout.printf ("APT CACHE FILES: %s\n", size.to_string());
return data;
}
public static int main (string[] args) {
Gtk.init (ref args);
File APT_CACHE_PATH = File.new_for_path ("/var/cache/apt/archives");
try {
get_folder_data (APT_CACHE_PATH, "", new Cancellable ());
} catch (Error e) {
stdout.printf ("ERROR: %s\n", e.message);
}
Gtk.main ();
return 0;
}
And the command I used for compile is the following:
valac --pkg gtk+-3.0 --pkg glib-2.0 --pkg gio-2.0 apt-cache.vala

Answer 1

If you run your app as a normal user, you have to exclude the "partial" dir, it has more restrictive permissions (0700):
drwx------ 2 _apt root 4096 Jul 29 11:36 /var/cache/apt/archives/partial
One way to exclude the partial dir is to just ignore any dir that is inaccessible:
int64[] data = new int64[2];
FileEnumerator enumerator = null;
try {
enumerator = file.enumerate_children (
"standard::*",
FileQueryInfoFlags.NOFOLLOW_SYMLINKS,
cancellable);
}
catch (IOError e) {
stderr.printf ("WARNING: Unable to get size of dir '%s': %s\n", file.get_path (), e.message);
data[0] = 0;
data[1] = 0;
return data;
}
In addition it might be a good idea to always explicitly ignore the partial folder.
If you are planning to make your utility useful for the root user as well, you might even think of adding a command line option like "--include-partial-dir".
Also the same thing can be done with simple bash commands which is much easier than writing your own program.
du -sh /var/cache/apt/archives
find /var/cache/apt/archives -type f | wc -l
Note that du and find also warn about the inaccessible partial dir:
$ du -sh /var/cache/apt/archives
du: cannot read directory '/var/cache/apt/archives/partial': Permission denied
4.6G /var/cache/apt/archives
$ find /var/cache/apt/archives -type f | wc -l
find: '/var/cache/apt/archives/partial': Permission denied
3732