Add json (un)marshalling methods on NullUUID

uuid.go

@@ -32,6 +32,7 @@ import (
 	"database/sql/driver"
 	"encoding/binary"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"hash"
 	"net"
@@ -344,6 +345,29 @@ func (u *NullUUID) Scan(src interface{}) error {
 	return u.UUID.Scan(src)
 }
 
+// MarshalJSON marshalls the NullUUID as nil or the nested UUID
+func (u NullUUID) MarshalJSON() ([]byte, error) {
+	if u.Valid == false {
+		return json.Marshal(nil)
+	}
+	return json.Marshal(u.UUID)
+}
+
+// UnmarshalJSON unmarshalls a NullUUID
+func (u *NullUUID) UnmarshalJSON(b []byte) error {
+	if bytes.Equal(b, []byte("null")) {
+		u.UUID, u.Valid = Nil, false
+		return nil
+	}
+
+	if err := json.Unmarshal(b, &u.UUID); err != nil {
+		return err
+	}
+	u.Valid = true
+
+	return nil
+}
+
 // FromBytes returns UUID converted from raw byte slice input.
 // It will return error if the slice isn't 16 bytes long.
 func FromBytes(input []byte) (u UUID, err error) {

uuid_test.go

@@ -23,6 +23,7 @@ package uuid
 
 import (
 	"bytes"
+	"encoding/json"
 	"testing"
 )
 
@@ -631,3 +632,46 @@ func TestNewV5(t *testing.T) {
 		t.Errorf("UUIDv3 generated same UUIDs for sane names in different namespaces: %s and %s", u1, u4)
 	}
 }
+
+func TestMarshalNullUUID(t *testing.T) {
+	u := NullUUID{UUID: NewV4(), Valid: true}
+	j, err := json.Marshal(u)
+	if err != nil {
+		t.Error("Couldn't marshal a valid NullUUID: ", err)
+	}
+
+	if string(j) != "\""+u.UUID.String()+"\"" {
+		t.Error("Marshaled NullUUID is incorrect: ", string(j))
+	}
+
+	nu := NullUUID{Valid: false}
+	j, err = json.Marshal(nu)
+	if err != nil {
+		t.Error("Couldn't marshal an invalid NullUUID: ", err)
+	}
+
+	if string(j) != "null" {
+		t.Error("Marshaled NullUUID is incorrect: ", string(j))
+	}
+}
+
+func TestUnmarshalNullUUID(t *testing.T) {
+	var u NullUUID
+	err := json.Unmarshal([]byte("null"), &u)
+	if err != nil {
+		t.Error("Couldn't Unmarshal an invalid NullUUID: ", err)
+	}
+
+	if u.Valid != false {
+		t.Error("Unmarshaled NullUUID is valid but shouldn't")
+	}
+
+	err = json.Unmarshal([]byte("\"886313e1-3b8a-5372-9b90-0c9aee199e5d\""), &u)
+	if err != nil {
+		t.Error("Couldn't Unmarshal an invalid NullUUID: ", err)
+	}
+
+	if u.Valid != true || u.UUID.String() != "886313e1-3b8a-5372-9b90-0c9aee199e5d" {
+		t.Error("Unmarshaled NullUUID is incorrect: ", u.Valid, u.UUID)
+	}
+}