Implement suspending the app using ctrl-z

Co-authored-by: Stefan Haller <stefan@haller-berlin.de>

pkg/gui/controllers/helpers/signal_handling.go

@@ -0,0 +1,59 @@
+//go:build !windows
+
+package helpers
+
+import (
+	"os"
+	"os/signal"
+	"syscall"
+
+	"github.com/sirupsen/logrus"
+	"golang.org/x/sys/unix"
+)
+
+func canSuspendApp() bool {
+	return true
+}
+
+func sendStopSignal() error {
+	return syscall.Kill(0, syscall.SIGSTOP)
+}
+
+// setForegroundPgrp sets the current process group as the foreground process group
+// for the terminal, allowing the program to read input after resuming from suspension.
+func setForegroundPgrp() error {
+	fd, err := unix.Open("/dev/tty", unix.O_RDWR, 0)
+	if err != nil {
+		return err
+	}
+	defer unix.Close(fd)
+
+	pgid := syscall.Getpgrp()
+
+	return unix.IoctlSetPointerInt(fd, unix.TIOCSPGRP, pgid)
+}
+
+func handleResumeSignal(log *logrus.Entry, onResume func() error) {
+	if err := setForegroundPgrp(); err != nil {
+		log.Warning(err)
+		return
+	}
+
+	if err := onResume(); err != nil {
+		log.Warning(err)
+	}
+}
+
+func installResumeSignalHandler(log *logrus.Entry, onResume func() error) {
+	go func() {
+		sigs := make(chan os.Signal, 1)
+		signal.Notify(sigs, syscall.SIGCONT)
+
+		for sig := range sigs {
+			switch sig {
+			case syscall.SIGCONT:
+				handleResumeSignal(log, onResume)
+			}
+		}
+	}()
+}