Organize backend into product executable and shared Go modules

backend/shared/errors/classified.go

@@ -0,0 +1,48 @@
+package merrors
+
+import "strings"
+
+type classifiedError struct {
+	base          error
+	code          error
+	msg           string
+	reason        string
+	publicMessage bool
+	argumentNames []string
+}
+
+func (e classifiedError) Error() string {
+	if e.publicMessage {
+		msg := strings.TrimSpace(e.msg)
+		if msg != "" {
+			return msg
+		}
+		if e.code != nil {
+			return e.code.Error()
+		}
+		if e.base != nil {
+			return e.base.Error()
+		}
+		return ""
+	}
+	return Wrap(e.base, e.msg).Error()
+}
+
+func (e classifiedError) Unwrap() []error {
+	causes := make([]error, 0, 2)
+	if e.base != nil {
+		causes = append(causes, e.base)
+	}
+	if e.code != nil {
+		causes = append(causes, e.code)
+	}
+	return causes
+}
+
+func (e classifiedError) Reason() string {
+	return strings.TrimSpace(e.reason)
+}
+
+func (e classifiedError) InvalidArgumentFields() []string {
+	return append([]string(nil), e.argumentNames...)
+}