fix: Don't setup unmonitored pipes to child processes.

ulauncher/utils/launch_detached.py

@@ -1,5 +1,6 @@
 import logging
 import os
+import sys
 
 from gi.repository import GLib
 
@@ -8,12 +9,38 @@
 logger = logging.getLogger()
 
 
+def detach_child():
+    """
+    A utility function which runs in the child process launched by spawn_async
+    and before execing the supplied command.
+    """
+    # Use setsid to take "session leader" status so that the child pid is
+    # definitely detached from the parent ulauncher process
+    os.setsid()
+
+    # Don't redirect the standard file descriptors unless connected to a terminal.
+    if not sys.stdout.isatty():
+        return
+
+    # Reopen the stdin, stdout, and stderr file descriptors to /dev/null. This
+    # ensures the stdout/stderr are no longer connected to the terminal. This
+    # serves a similar purpose as the standard "nohup" command. Any processes
+    # connected to the terminal will get the interrupt signal when "Ctrl-C" is
+    # called, so this redirection prevents the child process from exiting when
+    # ulauncher is interrupted. Unlike "nohup", stdout and stderr are not sent
+    # to a file but sent to /dev/null instead.
+    null_fp = open("/dev/null", "w+b")  # noqa: SIM115
+    null_fd = null_fp.fileno()
+    for fp in [sys.stdin, sys.stdout, sys.stderr]:
+        orig_fd = fp.fileno()
+        fp.close()
+        os.dup2(null_fd, orig_fd)
+
+
 def launch_detached(cmd):
-    cmd = (
-        ["systemd-run", "--user", "--scope", *cmd]
-        if SystemdController("ulauncher").is_active()
-        else ["setsid", "nohup", *cmd]
-    )
+    use_systemd_run = SystemdController("ulauncher").is_active()
+    if use_systemd_run:
+        cmd = ["systemd-run", "--user", "--scope", *cmd]
 
     env = dict(os.environ.items())
     # Make sure GDK apps aren't forced to use x11 on wayland due to ulauncher's need to run
@@ -27,8 +54,7 @@ def launch_detached(cmd):
             argv=cmd,
             envp=envp,
             flags=GLib.SpawnFlags.SEARCH_PATH_FROM_ENVP | GLib.SpawnFlags.SEARCH_PATH,
-            standard_output=True,
-            standard_error=True,
+            child_setup=None if use_systemd_run else detach_child,
         )
     except Exception:
         logger.exception('Could not launch "%s"', cmd)