Add json and envconfig serialization support for HexColor (#42)

hexcolor.go

@@ -2,12 +2,14 @@ package colorful
 
 import (
 	"database/sql/driver"
+	"encoding/json"
 	"fmt"
 	"reflect"
 )
 
 // A HexColor is a Color stored as a hex string "#rrggbb". It implements the
-// database/sql.Scanner and database/sql/driver.Value interfaces.
+// database/sql.Scanner, database/sql/driver.Value,
+// encoding/json.Unmarshaler and encoding/json.Marshaler interfaces.
 type HexColor Color
 
 type errUnsupportedType struct {
@@ -35,3 +37,31 @@ func (hc *HexColor) Value() (driver.Value, error) {
 func (e errUnsupportedType) Error() string {
 	return fmt.Sprintf("unsupported type: got %v, want a %s", e.got, e.want)
 }
+
+func (hc *HexColor) UnmarshalJSON(data []byte) error {
+	var hexCode string
+	if err := json.Unmarshal(data, &hexCode); err != nil {
+		return err
+	}
+
+	var col, err = Hex(hexCode)
+	if err != nil {
+		return err
+	}
+	*hc = HexColor(col)
+	return nil
+}
+
+func (hc HexColor) MarshalJSON() ([]byte, error) {
+	return json.Marshal(Color(hc).Hex())
+}
+
+// Decode - deserilize function for https://github.com/kelseyhightower/envconfig
+func (hc *HexColor) Decode(hexCode string) error {
+	var col, err = Hex(hexCode)
+	if err != nil {
+		return err
+	}
+	*hc = HexColor(col)
+	return nil
+}

hexcolor_test.go

@@ -1,6 +1,7 @@
 package colorful
 
 import (
+	"encoding/json"
 	"reflect"
 	"testing"
 )
@@ -28,3 +29,27 @@ func TestHexColor(t *testing.T) {
 		}
 	}
 }
+
+type CompositeType struct {
+	Name  string   `json:"name,omitempty"`
+	Color HexColor `json:"color,omitempty"`
+}
+
+func TestHexColorCompositeJson(t *testing.T) {
+	var obj = CompositeType{Name: "John", Color: HexColor{R: 1, G: 0, B: 1}}
+	var jsonData, err = json.Marshal(obj)
+	if err != nil {
+		t.Errorf("json.Marshall(obj) wrote %v", err)
+	}
+	var obj2 CompositeType
+	err = json.Unmarshal(jsonData, &obj2)
+
+	if err != nil {
+		t.Errorf("json.Unmarshall(%s) wrote %v", jsonData, err)
+	}
+
+	if !reflect.DeepEqual(obj2, obj) {
+		t.Errorf("json.Unmarshal(json.Marsrhall(obj)) != obj")
+	}
+
+}