Limit wait time for writes in mqtt output (#3699)

plugins/outputs/mqtt/mqtt.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
@@ -25,6 +26,9 @@ var sampleConfig = `
   # username = "telegraf"
   # password = "metricsmetricsmetricsmetrics"
 
+  ## Timeout for write operations. default: 5s
+  # timeout = "5s"
+
   ## client ID, if not set a random ID is generated
   # client_id = ""
 
@@ -149,7 +153,7 @@ func (m *MQTT) Write(metrics []telegraf.Metric) error {
 
 func (m *MQTT) publish(topic string, body []byte) error {
 	token := m.client.Publish(topic, byte(m.QoS), false, body)
-	token.Wait()
+	token.WaitTimeout(m.Timeout.Duration)
 	if token.Error() != nil {
 		return token.Error()
 	}
@@ -159,6 +163,11 @@ func (m *MQTT) publish(topic string, body []byte) error {
 func (m *MQTT) createOpts() (*paho.ClientOptions, error) {
 	opts := paho.NewClientOptions()
 
+	if m.Timeout.Duration < time.Second {
+		m.Timeout.Duration = 5 * time.Second
+	}
+	opts.WriteTimeout = m.Timeout.Duration
+
 	if m.ClientID != "" {
 		opts.SetClientID(m.ClientID)
 	} else {