fix(inputs.mqtt_consumer): Client logs via option (#13663)

plugins/inputs/mqtt_consumer/README.md

@@ -100,6 +100,12 @@ to use them.
   ## Use TLS but skip chain & host verification
   # insecure_skip_verify = false
 
+  ## Client trace messages
+  ## When set to true, and debug mode enabled in the agent settings, the MQTT
+  ## client's messages are included in telegraf logs. These messages are very
+  ## noisey, but essential for debugging issues.
+  # client_trace = false
+
   ## Data format to consume.
   ## Each data format has its own unique set of configuration options, read
   ## more about them here:

plugins/inputs/mqtt_consumer/logger.go

@@ -0,0 +1,17 @@
+package mqtt_consumer
+
+import (
+	"github.com/influxdata/telegraf"
+)
+
+type mqttLogger struct {
+	telegraf.Logger
+}
+
+func (l mqttLogger) Printf(fmt string, args ...interface{}) {
+	l.Logger.Debugf(fmt, args...)
+}
+
+func (l mqttLogger) Println(args ...interface{}) {
+	l.Logger.Debug(args...)
+}

plugins/inputs/mqtt_consumer/mqtt_consumer.go

@@ -70,6 +70,7 @@ type MQTTConsumer struct {
 	Password               config.Secret        `toml:"password"`
 	QoS                    int                  `toml:"qos"`
 	ConnectionTimeout      config.Duration      `toml:"connection_timeout"`
+	ClientTrace            bool                 `toml:"client_trace"`
 	MaxUndeliveredMessages int                  `toml:"max_undelivered_messages"`
 	parser                 telegraf.Parser
 
@@ -104,6 +105,14 @@ func (m *MQTTConsumer) SetParser(parser telegraf.Parser) {
 	m.parser = parser
 }
 func (m *MQTTConsumer) Init() error {
+	if m.ClientTrace {
+		log := &mqttLogger{m.Log}
+		mqtt.ERROR = log
+		mqtt.CRITICAL = log
+		mqtt.WARN = log
+		mqtt.DEBUG = log
+	}
+
 	m.state = Disconnected
 	if m.PersistentSession && m.ClientID == "" {
 		return errors.New("persistent_session requires client_id")

plugins/inputs/mqtt_consumer/sample.conf

@@ -63,6 +63,12 @@
   ## Use TLS but skip chain & host verification
   # insecure_skip_verify = false
 
+  ## Client trace messages
+  ## When set to true, and debug mode enabled in the agent settings, the MQTT
+  ## client's messages are included in telegraf logs. These messages are very
+  ## noisey, but essential for debugging issues.
+  # client_trace = false
+
   ## Data format to consume.
   ## Each data format has its own unique set of configuration options, read
   ## more about them here: