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A _posts/2020-09-28-gio-launch-set-terminal.md

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+---
+title: "Setting terminal to launch .desktop with GIO"
+categories:
+  - GTK
+tags:
+  - gtk
+  - linux
+  - en
+---
+
+When learning about Gemini today, I clicked on a `gemini://` link, set my Firefox open-with preference to a command line client and opened, but nothing happened.
+
+Searching for a way to launch a `.desktop` by command line, hoping for better debugging experience, I got `gtk-launch <.desktop name>`. With that name I assumed there was a GTK or GLib or G-something way to launch `.desktop` and Firefox was likely also using it. Using that command, again, no new terminal was launched but at least there was a line by shell spawned by gtk-launch complaining xterm not found.
+
+A quick search about how to set terminal to use with gtk-launch returned nothing but old and unanswered StackOverflow threads. Time to read the source. I've looked into GTK and GLib a little bit before, quite readable, so it should not be hard for me.
+
+In `gtk/gtk-launch.c` I found this:
+```c
+  if (!g_app_info_launch (info, l, launch_context, &error))
+```
+A G-something way, as I guessed.
+
+Searching for `g_app_info_launch` brought me to GIO, a part of GLib. Within that function I saw this:
+```c
+  return (* iface->launch) (appinfo, files, launch_context, error);
+```
+Looked like `GAppInfo` was an interface and I needed to dig into the used implementation.
+
+Back to gtk-launch, looking at what `info` variable was:
+```c
+  info = G_APP_INFO (g_desktop_app_info_new (desktop_file_name));
+```
+GDesktopAppInfo it was.
+
+In GDesktopAppInfo, digging into functions, I found out that it would use either `g_desktop_app_info_launch_uris_with_dbus` or `g_desktop_app_info_launch_uris_with_spawn`. The `*_with_spawn` one sounded simpler. Assuming those two ways would not differ to much in finding terminal emulators to use, I looked into that one and saw:
+
+```c
+      if (info->terminal && !prepend_terminal_to_vector (&argc, &argv))
+```
+`prepend_terminal_to_vector` was the routine for finding terminal emulators. It found within a few hard-coded names and fallback to `xterm` . There were `gnome-terminal`, `mate-terminal`, `xfce4-terminal`, `nxterm`, `color-xterm`, `rxvt`, `dtterm` and finally `xterm`. The one I used was not on the list.
+
+As I will likely not install xterm on my machine, I created an xterm link to my terminal and problem solved. gtk-launch and Firefox now launch command line tools successfully.