Fix MQTT input exits if Broker is not available on startup (#3202)

(cherry picked from commit 5488f4b3ac)

plugins/inputs/mqtt_consumer/README.md

@@ -13,6 +13,8 @@ The plugin expects messages in the
   servers = ["localhost:1883"]
   ## MQTT QoS, must be 0, 1, or 2
   qos = 0
+  ## Connection timeout for initial connection in seconds
+  connection_timeout = 30
 
   ## Topics to subscribe to
   topics = [

plugins/inputs/mqtt_consumer/mqtt_consumer.go

@@ -21,6 +21,7 @@ type MQTTConsumer struct {
 	Username          string
 	Password          string
 	QoS               int               `toml:"qos"`
+	ConnectionTimeout internal.Duration `toml:"connection_timeout"`
 
 	parser parsers.Parser
 
@@ -48,13 +49,15 @@ type MQTTConsumer struct {
 	// keep the accumulator internally:
 	acc telegraf.Accumulator
 
-	started bool
+	connected bool
 }
 
 var sampleConfig = `
   servers = ["localhost:1883"]
   ## MQTT QoS, must be 0, 1, or 2
   qos = 0
+  ## Connection timeout for initial connection in seconds
+  connection_timeout = 30
 
   ## Topics to subscribe to
   topics = [
@@ -103,7 +106,7 @@ func (m *MQTTConsumer) SetParser(parser parsers.Parser) {
 func (m *MQTTConsumer) Start(acc telegraf.Accumulator) error {
 	m.Lock()
 	defer m.Unlock()
-	m.started = false
+	m.connected = false
 
 	if m.PersistentSession && m.ClientID == "" {
 		return fmt.Errorf("ERROR MQTT Consumer: When using persistent_session" +
@@ -115,26 +118,40 @@ func (m *MQTTConsumer) Start(acc telegraf.Accumulator) error {
 		return fmt.Errorf("MQTT Consumer, invalid QoS value: %d", m.QoS)
 	}
 
+	if int(m.ConnectionTimeout.Duration) <= 0 {
+		return fmt.Errorf("MQTT Consumer, invalid connection_timeout value: %d", m.ConnectionTimeout)
+	}
+
 	opts, err := m.createOpts()
 	if err != nil {
 		return err
 	}
 
 	m.client = mqtt.NewClient(opts)
-	if token := m.client.Connect(); token.Wait() && token.Error() != nil {
-		return token.Error()
-	}
-
 	m.in = make(chan mqtt.Message, 1000)
 	m.done = make(chan struct{})
 
+	m.connect()
+
+	return nil
+}
+
+func (m *MQTTConsumer) connect() error {
+	if token := m.client.Connect(); token.Wait() && token.Error() != nil {
+		err := token.Error()
+		log.Printf("D! MQTT Consumer, connection error - %v", err)
+
+		return err
+	}
+
 	go m.receiver()
 
 	return nil
 }
+
 func (m *MQTTConsumer) onConnect(c mqtt.Client) {
 	log.Printf("I! MQTT Client Connected")
-	if !m.PersistentSession || !m.started {
+	if !m.PersistentSession || !m.connected {
 		topics := make(map[string]byte)
 		for _, topic := range m.Topics {
 			topics[topic] = byte(m.QoS)
@@ -145,7 +162,7 @@ func (m *MQTTConsumer) onConnect(c mqtt.Client) {
 			m.acc.AddError(fmt.Errorf("E! MQTT Subscribe Error\ntopics: %s\nerror: %s",
 				strings.Join(m.Topics[:], ","), subscribeToken.Error()))
 		}
-		m.started = true
+		m.connected = true
 	}
 	return
 }
@@ -186,18 +203,27 @@ func (m *MQTTConsumer) recvMessage(_ mqtt.Client, msg mqtt.Message) {
 func (m *MQTTConsumer) Stop() {
 	m.Lock()
 	defer m.Unlock()
+
+	if m.connected {
 		close(m.done)
 		m.client.Disconnect(200)
-	m.started = false
+		m.connected = false
+	}
 }
 
 func (m *MQTTConsumer) Gather(acc telegraf.Accumulator) error {
+	if !m.connected {
+		m.connect()
+	}
+
 	return nil
 }
 
 func (m *MQTTConsumer) createOpts() (*mqtt.ClientOptions, error) {
 	opts := mqtt.NewClientOptions()
 
+	opts.ConnectTimeout = m.ConnectionTimeout.Duration
+
 	if m.ClientID == "" {
 		opts.SetClientID("Telegraf-Consumer-" + internal.RandomString(5))
 	} else {
@@ -238,6 +264,7 @@ func (m *MQTTConsumer) createOpts() (*mqtt.ClientOptions, error) {
 	opts.SetCleanSession(!m.PersistentSession)
 	opts.SetOnConnectHandler(m.onConnect)
 	opts.SetConnectionLostHandler(m.onConnectionLost)
+
 	return opts, nil
 }
 

plugins/inputs/mqtt_consumer/mqtt_consumer_test.go

@@ -26,7 +26,9 @@ func newTestMQTTConsumer() (*MQTTConsumer, chan mqtt.Message) {
 		Servers:   []string{"localhost:1883"},
 		in:        in,
 		done:      make(chan struct{}),
+		connected: true,
 	}
+
 	return n, in
 }
 
@@ -131,6 +133,7 @@ func TestRunParserAndGather(t *testing.T) {
 	n, in := newTestMQTTConsumer()
 	acc := testutil.Accumulator{}
 	n.acc = &acc
+
 	defer close(n.done)
 
 	n.parser, _ = parsers.NewInfluxParser()