Add leveled logging (#1249)

Co-authored-by: Ibrahim Jarif <ibrahim@dgraph.io>

logger.go

@@ -62,24 +62,44 @@ func (opt *Options) Debugf(format string, v ...interface{}) {
 	opt.Logger.Debugf(format, v...)
 }
 
+type loggingLevel int
+
+const (
+	DEBUG loggingLevel = iota
+	INFO
+	WARNING
+	ERROR
+)
+
 type defaultLog struct {
 	*log.Logger
+	level loggingLevel
 }
 
-var defaultLogger = &defaultLog{Logger: log.New(os.Stderr, "badger ", log.LstdFlags)}
+func defaultLogger(level loggingLevel) *defaultLog {
+	return &defaultLog{Logger: log.New(os.Stderr, "badger ", log.LstdFlags), level: level}
+}
 
 func (l *defaultLog) Errorf(f string, v ...interface{}) {
-	l.Printf("ERROR: "+f, v...)
+	if l.level <= ERROR {
+		l.Printf("ERROR: "+f, v...)
+	}
 }
 
 func (l *defaultLog) Warningf(f string, v ...interface{}) {
-	l.Printf("WARNING: "+f, v...)
+	if l.level <= WARNING {
+		l.Printf("WARNING: "+f, v...)
+	}
 }
 
 func (l *defaultLog) Infof(f string, v ...interface{}) {
-	l.Printf("INFO: "+f, v...)
+	if l.level <= INFO {
+		l.Printf("INFO: "+f, v...)
+	}
 }
 
 func (l *defaultLog) Debugf(f string, v ...interface{}) {
-	l.Printf("DEBUG: "+f, v...)
+	if l.level <= DEBUG {
+		l.Printf("DEBUG: "+f, v...)
+	}
 }

options.go

@@ -154,7 +154,7 @@ func DefaultOptions(path string) Options {
 		ValueLogMaxEntries:            1000000,
 		ValueThreshold:                32,
 		Truncate:                      false,
-		Logger:                        defaultLogger,
+		Logger:                        defaultLogger(INFO),
 		LogRotatesToFlush:             2,
 		EventLogging:                  false,
 		EncryptionKey:                 []byte{},
@@ -217,6 +217,17 @@ func (opt Options) WithValueDir(val string) Options {
 	return opt
 }
 
+// WithLoggingLevel returns a new Options value with logging level of the
+// default logger set to the given value.
+// LoggingLevel sets the level of logging. It should be one of DEBUG, INFO,
+// WARNING or ERROR levels.
+//
+// The default value of LoggingLevel is INFO.
+func (opt Options) WithLoggingLevel(val loggingLevel) Options {
+	opt.Logger = defaultLogger(val)
+	return opt
+}
+
 // WithSyncWrites returns a new Options value with SyncWrites set to the given value.
 //
 // When SyncWrites is true all writes are synced to disk. Setting this to false would achieve better