Fix for #4789 to allow a restart of a shutdown server instance.

Signed-off-by: Derek Collison <derek@nats.io>

server/server.go

@@ -2083,6 +2083,11 @@ func (s *Server) Start() {
 
 	defer s.Noticef("Server is ready")
 
+	// Check is this may be a restart.
+	if s.startupComplete == nil {
+		s.startupComplete = make(chan struct{})
+	}
+
 	// Check for insecure configurations.
 	s.checkAuthforWarnings()
 
@@ -2340,7 +2345,10 @@ func (s *Server) Start() {
 	}
 
 	// We've finished starting up.
-	close(s.startupComplete)
+	if s.startupComplete != nil {
+		close(s.startupComplete)
+		s.startupComplete = nil
+	}
 
 	// Wait for clients.
 	if !opts.DontListen {

server/server_test.go

@@ -2107,3 +2107,14 @@ func TestServerAuthBlockAndSysAccounts(t *testing.T) {
 	_, err = nats.Connect(s.ClientURL())
 	require_Error(t, err, nats.ErrAuthorization, errors.New("nats: Authorization Violation"))
 }
+
+// https://github.com/nats-io/nats-server/issues/4789
+func TestServerRestartAfterShutdown(t *testing.T) {
+	opts := DefaultTestOptions
+	opts.Port = -1
+	s := RunServer(&opts)
+	s.Shutdown()
+	s.WaitForShutdown()
+	s.Start()
+	defer s.Shutdown()
+}