Glib XDG Migration Cheat Sheet

If you are maintaining a Linux Glib-based or GTK application for some time you might want to migrate it to the XDG way of user data layout. This is something I had to do for Liferea (around since 2003) recently. Also when creating a new application you might ask yourself where to put the user data. This post tries to describe how to access the correct paths using Glib.

1. Preparation: Categorize your data

Determine what types of data you have. The specification knows three major directories:
  1. $XDG_DATA_HOME: usually ~/.local/share
  2. $XDG_CONFIG_HOME: usually ~/.config
  3. $XDG_CACHE_HOME: usually ~/.cache
In each of the directories your application should create a subfolder with the unique name of the application and place relevant files there. While volatile cache files go into ~/.cache, persistent important data should go to ~/.local/share and all configuration to ~/.config.

2. Migrate the code

The simple task is to rewrite the old code creating directory paths some arbitrary way to use XDG style directory paths now. As the specification is non-trivial when finding the directory base paths (via multiple paths in $XDG_DATA_DIRS and $XDG_CONFIG_DIRS) it might be good to rely on a library for doing this.

2.1 Using Glib

When developing for GTK or maybe only using Glib one already gets support since GTK uses Glib and Glib 2.6 introduced support for the XDG base directory specification. So with Glib use the following methods to find the target directories:
$XDG_DATA_HOMEg_get_user_data_dir()
$XDG_CONFIG_HOMEg_get_user_config_dir()
$XDG_CACHE_HOMEg_get_user_cache_dir()
Given your application being named "coolApp" and you want to create a cache file named "render.dat" you could use the following C snippet:
g_build_filename (g_get_user_cache_dir (), "coolApp", "render.dat", NULL);
to produce a path. Most likely you'll get something like "/home/joe/.cache/coolApp/render.dat".

2.2 Using wxWidgets

When programming for wxWidgets you need to use the wxStandardPaths class. The methods are
$XDG_DATA_HOMEwxStandardPaths::GetDataDir()
$XDG_CONFIG_HOMEwxStandardPaths::GetConfigDir()
$XDG_CACHE_HOMEwxStandardPaths::GetLocalDataDir()

2.3 With KDE

Since KDE 3.2 it also supports the XDG base specification. But honestly: googling our trying to browse the KDE API I couldn't find any pointers on how to do it. If you know please leave a comment!