Add custom sorting function in text formatter

text_formatter.go

@@ -55,6 +55,9 @@ type TextFormatter struct {
 	// be desired.
 	DisableSorting bool
 
+	// The keys sorting function, when uninitialized it uses sort.Strings.
+	SortingFunc func([]string)
+
 	// Disables the truncation of the level text to 4 characters.
 	DisableLevelTruncation bool
 
@@ -73,7 +76,7 @@ type TextFormatter struct {
 	//         FieldKeyMsg:   "@message"}}
 	FieldMap FieldMap
 
-	sync.Once
+	terminalInitOnce sync.Once
 }
 
 func (f *TextFormatter) init(entry *Entry) {
@@ -111,8 +114,29 @@ func (f *TextFormatter) Format(entry *Entry) ([]byte, error) {
 		keys = append(keys, k)
 	}
 
+	fixedKeys := make([]string, 0, 3+len(entry.Data))
+	if !f.DisableTimestamp {
+		fixedKeys = append(fixedKeys, f.FieldMap.resolve(FieldKeyTime))
+	}
+	fixedKeys = append(fixedKeys, f.FieldMap.resolve(FieldKeyLevel))
+	if entry.Message != "" {
+		fixedKeys = append(fixedKeys, f.FieldMap.resolve(FieldKeyMsg))
+	}
+
 	if !f.DisableSorting {
-		sort.Strings(keys)
+		if f.SortingFunc == nil {
+			sort.Strings(keys)
+			fixedKeys = append(fixedKeys, keys...)
+		} else {
+			if !f.isColored() {
+				fixedKeys = append(fixedKeys, keys...)
+				f.SortingFunc(fixedKeys)
+			} else {
+				f.SortingFunc(keys)
+			}
+		}
+	} else {
+		fixedKeys = append(fixedKeys, keys...)
 	}
 
 	var b *bytes.Buffer
@@ -122,7 +146,7 @@ func (f *TextFormatter) Format(entry *Entry) ([]byte, error) {
 		b = &bytes.Buffer{}
 	}
 
-	f.Do(func() { f.init(entry) })
+	f.terminalInitOnce.Do(func() { f.init(entry) })
 
 	timestampFormat := f.TimestampFormat
 	if timestampFormat == "" {
@@ -131,15 +155,19 @@ func (f *TextFormatter) Format(entry *Entry) ([]byte, error) {
 	if f.isColored() {
 		f.printColored(b, entry, keys, timestampFormat)
 	} else {
-		if !f.DisableTimestamp {
-			f.appendKeyValue(b, f.FieldMap.resolve(FieldKeyTime), entry.Time.Format(timestampFormat))
-		}
-		f.appendKeyValue(b, f.FieldMap.resolve(FieldKeyLevel), entry.Level.String())
-		if entry.Message != "" {
-			f.appendKeyValue(b, f.FieldMap.resolve(FieldKeyMsg), entry.Message)
-		}
-		for _, key := range keys {
-			f.appendKeyValue(b, key, entry.Data[key])
+		for _, key := range fixedKeys {
+			var value interface{}
+			switch key {
+			case f.FieldMap.resolve(FieldKeyTime):
+				value = entry.Time.Format(timestampFormat)
+			case f.FieldMap.resolve(FieldKeyLevel):
+				value = entry.Level.String()
+			case f.FieldMap.resolve(FieldKeyMsg):
+				value = entry.Message
+			default:
+				value = entry.Data[key]
+			}
+			f.appendKeyValue(b, key, value)
 		}
 	}