When using ruby better errors gem and emacs restclient package, When the Api has an error the raw html of better errors is the response so in order to filter the filename and line you can use this function

better-errors-file.el

(defun better-errors-file ()
    (interactive)
    (let ((root (libxml-parse-html-region (point-min) (point-max))))
      (message "file: %s at line: %s"
               (dom-attr (dom-by-class root "application") 'data-full-filename)
               (dom-attr (dom-by-class root "application") 'data-line))))