@dwp/govuk-casa/src/middleware/post.js

A framework for building GOVUK Collect-And-Submit-Applications

// 2 middleware: one as a fallback 404 handler, one to handle thrown errors
import logger from "../lib/logger.js";

/**
 * @typedef {import("express").RequestHandler} RequestHandler
 * @access private
 */

const log = logger("middleware:post");

/** @returns {RequestHandler[]} Middleware functions */
export default function postMiddleware() {
  return [
    (req, res) => {
      res.status(404).render("casa/errors/404.njk");
    },
    /* eslint-disable-next-line no-unused-vars */
    (err, req, res, next) => {
      // In some cases, an error may have been thrown before the template assets
      // have had a chance to initialise. So we use a hardcoded template in
      // these cases to ensure the user sees an appropriate message.
      let TEMPLATE = "casa/errors/500.njk";
      if (!res.locals.t) {
        res.locals.t = () => "";
        res.locals.casa = {
          ...res.locals?.casa,
          mountUrl: `${req.baseUrl}/`,
        };
        TEMPLATE = "casa/errors/static.njk";
      }

      // CSRF token is invalid in some way
      if (err?.code === "EBADCSRFTOKEN") {
        log.info(
          "CSRF validation has failed. This may be caused by the user submitting a stale form from a previous session [EBADCSRFTOKEN]",
        );
        return res
          .status(403)
          .render(TEMPLATE, { errorCode: "bad_csrf_token", error: err });
      }

      // Body parsing verification check failed
      if (err?.type === "entity.verify.failed") {
        log.info(
          "Body parser verification has failed. This has been caused by the user submitting a payload containing invalid data [entity.verify.failed]",
        );
        return res
          .status(403)
          .render(TEMPLATE, { errorCode: "invalid_payload", error: err });
      }

      // Too many parameters submitted
      if (err?.type === "parameters.too.many") {
        log.info(
          "The request contains more parameters than is currently allowed [parameters.too.many]",
        );
        return res.status(413).render(TEMPLATE, {
          errorCode: "parameter_limit_exceeded",
          error: err,
        });
      }

      // Overall payload too large
      if (err?.type === "entity.too.large") {
        log.info(
          `The request payload is too large. Received ${err.length}b with a maximum of ${err.limit}b [parameters.too.many]`,
        );
        return res
          .status(413)
          .render(TEMPLATE, { errorCode: "payload_size_exceeded", error: err });
      }

      // Unaccept request method
      if (err?.code === "unaccepted_request_method") {
        log.info(err.message);
        return res.status(400).render(TEMPLATE, {
          errorCode: "unaccepted_request_method",
          error: err,
        });
      }

      // Unknown error
      log.error(`Unknown error: ${err.message}; stacktrace: ${err.stack}`);
      return res.status(200).render(TEMPLATE, { error: err });
    },
  ];
}