refactor backend API structure

internal/httpapi/admin/shared/request_error.go

@@ -0,0 +1,31 @@
+package shared
+
+import "errors"
+
+type requestError struct {
+	detail string
+}
+
+func (e *requestError) Error() string {
+	return e.detail
+}
+
+func newRequestError(detail string) error {
+	return &requestError{detail: detail}
+}
+
+func NewRequestError(detail string) error {
+	return newRequestError(detail)
+}
+
+func requestErrorDetail(err error) (string, bool) {
+	var reqErr *requestError
+	if errors.As(err, &reqErr) {
+		return reqErr.detail, true
+	}
+	return "", false
+}
+
+func RequestErrorDetail(err error) (string, bool) {
+	return requestErrorDetail(err)
+}