fix #260, support rename for extra.SupportPrivateFields

Author: taowen

extra/privat_fields.go

@@ -3,6 +3,7 @@ package extra
 import (
 	"github.com/json-iterator/go"
 	"unicode"
+	"strings"
 )
 
 // SupportPrivateFields include private fields when encoding/decoding
@@ -18,8 +19,37 @@ func (extension *privateFieldsExtension) UpdateStructDescriptor(structDescriptor
 	for _, binding := range structDescriptor.Fields {
 		isPrivate := unicode.IsLower(rune(binding.Field.Name()[0]))
 		if isPrivate {
-			binding.FromNames = []string{binding.Field.Name()}
-			binding.ToNames = []string{binding.Field.Name()}
+			tag, hastag := binding.Field.Tag().Lookup("json")
+			if !hastag {
+				binding.FromNames = []string{binding.Field.Name()}
+				binding.ToNames = []string{binding.Field.Name()}
+				continue
+			}
+			tagParts := strings.Split(tag, ",")
+			names := calcFieldNames(binding.Field.Name(), tagParts[0], tag)
+			binding.FromNames = names
+			binding.ToNames = names
 		}
 	}
 }
+
+func calcFieldNames(originalFieldName string, tagProvidedFieldName string, wholeTag string) []string {
+	// ignore?
+	if wholeTag == "-" {
+		return []string{}
+	}
+	// rename?
+	var fieldNames []string
+	if tagProvidedFieldName == "" {
+		fieldNames = []string{originalFieldName}
+	} else {
+		fieldNames = []string{tagProvidedFieldName}
+	}
+	// private?
+	isNotExported := unicode.IsLower(rune(originalFieldName[0]))
+	if isNotExported {
+		fieldNames = []string{}
+	}
+	return fieldNames
+}
+