daemon: added --autoclose flag

This is useful when the cli daemon is launched from an external process
to avoid leaving zombie process if the parent process unexpectedly dies.

Author: cmaglie

Diff for: cli/daemon/daemon.go

@@ -19,6 +19,8 @@ package daemon
 
 import (
 	"fmt"
+	"io"
+	"io/ioutil"
 	"log"
 	"net"
 	"net/http"
@@ -39,16 +41,20 @@ const (
 
 // NewCommand created a new `daemon` command
 func NewCommand() *cobra.Command {
-	return &cobra.Command{
+	cmd := &cobra.Command{
 		Use:     "daemon",
 		Short:   fmt.Sprintf("Run as a daemon on port %s", port),
 		Long:    "Running as a daemon the initialization of cores and libraries is done only once.",
 		Example: "  " + os.Args[0] + " daemon",
 		Args:    cobra.NoArgs,
 		Run:     runDaemonCommand,
 	}
+	cmd.Flags().BoolVar(&autoclose, "autoclose", false, "Do not daemonize (terminate daemon process when the parent process dies)")
+	return cmd
 }
 
+var autoclose bool
+
 func runDaemonCommand(cmd *cobra.Command, args []string) {
 	s := grpc.NewServer()
 
@@ -68,13 +74,20 @@ func runDaemonCommand(cmd *cobra.Command, args []string) {
 	// register the monitors service
 	srv_monitor.RegisterMonitorServer(s, &daemon.MonitorService{})
 
+	if autoclose {
+		// When parent process ends terminate also the daemon
+		go func() {
+			// stdin is closed when the controlling parent process ends
+			_, _ = io.Copy(ioutil.Discard, os.Stdin)
+			os.Exit(0)
+		}()
+	}
+
 	lis, err := net.Listen("tcp", port)
 	if err != nil {
 		log.Fatalf("failed to listen: %v", err)
 	}
 	if err := s.Serve(lis); err != nil {
 		log.Fatalf("failed to serve: %v", err)
 	}
-
-	fmt.Println("Done serving")
 }