with fields

fields.go

@@ -0,0 +1,6 @@
+package log
+
+func (l myLogger) WithFields(fields Fields) Logger {
+	l.data = fields
+	return l
+}

logger.go

@@ -29,4 +29,6 @@ type Logger interface {
 	End(a ...interface{})
 
 	Level(uint8) Logger
+
+	WithFields(fields Fields) Logger
 }

my_logger.go

@@ -13,22 +13,41 @@ var (
 	DefaultTimeFormat = time.RFC3339
 )
 
+type Fields map[string]interface{}
+
 type myLogger struct {
 	Writer io.Writer
 	prefix string
 	begin  time.Time
 	level  uint8
+	data   Fields
 }
 
 func logPrefix(level uint8) string {
 	return fmt.Sprintf("time=%q level=%s function=%s", time.Now().Format(DefaultTimeFormat), unmarshalLevel(level), funcName())
 }
 
+func (fields Fields) String() string {
+	if len(fields) == 0 {
+		return ""
+	}
+	var buffer strings.Builder
+	for k, v := range fields {
+		switch v := v.(type) {
+		case string:
+			buffer.WriteString(fmt.Sprintf(" %s=%q", k, v))
+		default:
+			buffer.WriteString(fmt.Sprintf(" %s=%v", k, v))
+		}
+	}
+	return buffer.String()
+}
+
 func (l myLogger) log(level uint8, s ...interface{}) {
 	if l.Writer == nil {
 		return
 	}
-	f := fmt.Sprintf("%s%s msg=%q", logPrefix(level), l.prefix, fmt.Sprint(s...))
+	f := fmt.Sprintf("%s%s msg=%q %s", logPrefix(level), l.prefix, fmt.Sprint(s...), l.data)
 	fmt.Fprintln(l.Writer, f)
 }
 
@@ -36,9 +55,8 @@ func (l myLogger) logf(level uint8, format string, s ...interface{}) {
 	if l.Writer == nil {
 		return
 	}
-	format = fmt.Sprintf("%%s %%s msg=\"%s\"\n", format)
+	format = fmt.Sprintf("%%s %%s msg=\"%s\" %s\n", format, l.data)
 	s = append([]interface{}{logPrefix(level), l.prefix}, s...)
-
 	fmt.Fprintf(l.Writer, format, s...)
 }