listener: Remove unused state metrics

... and added some missing docstrings for public types/methods.

listener/listener.go

@@ -73,7 +73,6 @@ func StartListener(c *config.Config) (_ *Listener, err error) {
 	go listener.listenUDP(sc)
 
 	log.Printf("UDP listener publishing to [%s] at %s", c.NATSSubject[0], c.NATSAddress)
-	listener.notifyState("ready")
 
 	return listener, nil
 }
@@ -93,11 +92,13 @@ func StartHTTPListener(c *config.Config) (*Listener, error) {
 	go listener.listenHTTP(server)
 
 	log.Printf("HTTP listener publishing to [%s] at %s", c.NATSSubject[0], c.NATSAddress)
-	listener.notifyState("ready")
 
 	return listener, nil
 }
 
+// Listener accepts measurements in InfluxDB Line Protocol format via
+// UDP or HTTP, batches them and then publishes them to a NATS
+// subject.
 type Listener struct {
 	c     *config.Config
 	nc    *nats.Conn
@@ -118,6 +119,8 @@ func (l *Listener) Ready() <-chan struct{} {
 	return l.ready
 }
 
+// Stop shuts down a running listener. It should be called exactly
+// once for every Listener instance.
 func (l *Listener) Stop() {
 	close(l.stop)
 	l.wg.Wait()
@@ -147,7 +150,6 @@ func newListener(c *config.Config) (*Listener, error) {
 	nc.Opts.MaxReconnect = -1
 	l.nc = nc
 
-	l.notifyState("boot")
 	return l, nil
 }
 
@@ -302,19 +304,6 @@ func (l *Listener) startStatistician() {
 	}
 }
 
-var notifyLine = lineformatter.New("spout_mon", nil, "type", "state", "pid")
-
-func (l *Listener) notifyState(state string) {
-	line := notifyLine.Format(nil, "listener", state, os.Getpid())
-	if err := l.nc.Publish(l.c.NATSSubjectMonitor, line); err != nil {
-		l.handleNatsError(err)
-		return
-	}
-	if err := l.nc.Flush(); err != nil {
-		l.handleNatsError(err)
-	}
-}
-
 type timeouter interface {
 	Timeout() bool
 }