Persist offline mqtt events in the queueDir and replay (#7037)

vendor/github.com/eclipse/paho.mqtt.golang/trace.go

@@ -14,23 +14,27 @@
 
 package mqtt
 
-import (
-	"io/ioutil"
-	"log"
+type (
+	// Logger interface allows implementations to provide to this package any
+	// object that implements the methods defined in it.
+	Logger interface {
+		Println(v ...interface{})
+		Printf(format string, v ...interface{})
+	}
+
+	// NOOPLogger implements the logger that does not perform any operation
+	// by default. This allows us to efficiently discard the unwanted messages.
+	NOOPLogger struct{}
 )
 
+func (NOOPLogger) Println(v ...interface{}) {}
+func (NOOPLogger) Printf(format string, v ...interface{}) {}
+
 // Internal levels of library output that are initialised to not print
 // anything but can be overridden by programmer
 var (
-	ERROR    *log.Logger
-	CRITICAL *log.Logger
-	WARN     *log.Logger
-	DEBUG    *log.Logger
+	ERROR    Logger = NOOPLogger{}
+	CRITICAL Logger = NOOPLogger{}
+	WARN     Logger = NOOPLogger{}
+	DEBUG    Logger = NOOPLogger{}
 )
-
-func init() {
-	ERROR = log.New(ioutil.Discard, "", 0)
-	CRITICAL = log.New(ioutil.Discard, "", 0)
-	WARN = log.New(ioutil.Discard, "", 0)
-	DEBUG = log.New(ioutil.Discard, "", 0)
-}