Added error wrapper (#252)

* Added error wrapper

* Keep the same message format

errorcode.go

@@ -163,3 +163,19 @@ var errorReasons = map[ErrorCode][]byte{
 	CodeAddrFamilyNotSupported: []byte("Address Family not Supported"),
 	CodePeerAddrFamilyMismatch: []byte("Peer Address Family Mismatch"),
 }
+
+// TurnError represents an error from a TURN response.
+type TurnError struct {
+	StunMessageType MessageType
+	ErrorCodeAttr   ErrorCodeAttribute
+}
+
+// Error returns the formatted TURN error message.
+func (e TurnError) Error() string {
+	return fmt.Sprintf("%s (error %s)", e.StunMessageType, e.ErrorCodeAttr.String())
+}
+
+// String returns the error message as a string.
+func (e TurnError) String() string {
+	return e.Error()
+}

errorcode_test.go

@@ -89,3 +89,16 @@ func TestErrorCode(t *testing.T) {
 	attr.Reason = make([]byte, 2048)
 	assert.Error(t, attr.AddTo(m), "should error")
 }
+
+func TestTurnError(t *testing.T) {
+	te := TurnError{
+		StunMessageType: NewType(MethodCreatePermission, ClassErrorResponse),
+		ErrorCodeAttr: ErrorCodeAttribute{
+			Code:   CodeForbidden,
+			Reason: []byte("Forbidden"),
+		},
+	}
+	expected := "CreatePermission error response (error 403: Forbidden)"
+	assert.Equal(t, expected, te.Error())
+	assert.Equal(t, expected, te.String())
+}