refactoring: add common package

The common package defines the interfaces that a protocol must implement
and contain code that can be shared among supported protocols.

This way should be easier to support new protocols

examples/ldapauthserver/logger/logger.go

@@ -5,7 +5,6 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
-	"sync"
 
 	"github.com/rs/zerolog"
 	lumberjack "gopkg.in/natefinch/lumberjack.v2"
@@ -38,9 +37,9 @@ func InitLogger(logFilePath string, logMaxSize, logMaxBackups, logMaxAge int, lo
 		})
 		EnableConsoleLogger(level)
 	} else {
-		logger = zerolog.New(logSyncWrapper{
+		logger = zerolog.New(&logSyncWrapper{
 			output: os.Stdout,
-			lock:   new(sync.Mutex)})
+		})
 		consoleLogger = zerolog.Nop()
 	}
 	logger.Level(level)

examples/ldapauthserver/logger/sync_wrapper.go

@@ -6,12 +6,12 @@ import (
 )
 
 type logSyncWrapper struct {
-	lock   *sync.Mutex
+	sync.Mutex
 	output *os.File
 }
 
-func (l logSyncWrapper) Write(b []byte) (n int, err error) {
-	l.lock.Lock()
-	defer l.lock.Unlock()
+func (l *logSyncWrapper) Write(b []byte) (n int, err error) {
+	l.Lock()
+	defer l.Unlock()
 	return l.output.Write(b)
 }