systemd socket activation compatibility

grace.go

@@ -25,7 +25,7 @@ var (
 
 const (
 	// Used to indicate a graceful restart in the new process.
-	envCountKey = "GRACE"
+	envCountKey = "LISTEN_FDS"
 
 	// The error returned by the standard library when the socket is closed.
 	errClosed = "use of closed network connection"
@@ -132,6 +132,9 @@ func Wait(listeners []Listener) (err error) {
 		sig := <-ch
 		switch sig {
 		case syscall.SIGTERM:
+			if os.Getppid() == 1 { // init provided sockets dont close
+				return
+			}
 			var wg sync.WaitGroup
 			wg.Add(len(listeners))
 			for _, l := range listeners {
@@ -182,7 +185,11 @@ func Inherit() (listeners []Listener, err error) {
 // Start the Close process in the parent. This does not wait for the
 // parent to close and simply sends it the TERM signal.
 func CloseParent() error {
-	return syscall.Kill(os.Getppid(), syscall.SIGTERM)
+	ppid := os.Getppid()
+	if ppid == 1 { // init provided sockets, for example systemd
+		return nil
+	}
+	return syscall.Kill(ppid, syscall.SIGTERM)
 }
 
 // Restart the process passing the given listeners to the new process.

gracehttp/http.go

@@ -83,9 +83,14 @@ func Serve(givenHandlers ...Handler) error {
 			return fmt.Errorf("Failed to close parent: %s", err)
 		}
 		if *verbose {
+			ppid := os.Getppid()
+			if ppid == 1 {
+				log.Printf("Listening on init activated %s", pprintAddr(listeners))
+			} else {
 				log.Printf(
 					"Graceful handoff of %s with new pid %d and old pid %d.",
-				pprintAddr(listeners), os.Getpid(), os.Getppid())
+					pprintAddr(listeners), os.Getpid(), ppid)
+			}
 		}
 	} else if err == grace.ErrNotInheriting {
 		listeners, err = handlers.newListeners()
@@ -103,7 +108,7 @@ func Serve(givenHandlers ...Handler) error {
 		return err
 	}
 	if *verbose {
-		return fmt.Errorf("Exiting pid %d.", os.Getpid())
+		log.Printf("Exiting pid %d.", os.Getpid())
 	}
 	return nil
 }