add error code in interface to get custom codes

Author: Aryan Tikarya

errors.go

@@ -59,6 +59,13 @@ type marshalable interface {
 	json.Unmarshaler
 }
 
+// Error wraps RPC errors, which contain an error code in addition to the message.
+type Error interface {
+	Error() string  // returns the message
+	ErrorCode() int // returns the code
+}
+
+// DataError contains extra data to explain the error
 type DataError interface {
 	Error() string          // returns the message
 	ErrorData() interface{} // returns the error data

handler.go

@@ -365,7 +365,13 @@ func (s *handler) createError(err error) *respError {
 		}
 	}
 
-	if de, ok := err.(DataError); ok {
+	var err2 Error
+	if errors.As(err, &err2) {
+		out.Code = ErrorCode(err2.ErrorCode())
+	}
+
+	var de DataError
+	if errors.As(err, &de) {
 		out.Data = de.ErrorData()
 	}