@dwp/govuk-casa/dist/middleware/strip-proxy-path.js

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

"use strict";
// Strip any "proxy path" prefix present on the request URL
//
// The default "mountUrl" will be match whatever path that the CASA app
// instance will be mounted onto. So if you mount on `/a/b/c` then all
// URLs generated for the browser will be prefixed with `/a/b/c`.
//
// Defining a `mountUrl` will change that behaviour into a "proxy mode".
// This mode assumes you have a forwarding proxy that will alter
// the incoming request paths from `mountUrl` to the original path you
// have mounted this CASA app instance onto.
//
// For example, if you mount the app on `/a/b/c/x`, but want the browser
// URLs to just use the `/x` prefix, then pass a `mountUrl` of `/x`.
//
// See docs in `docs/guides/setup-behind-a-proxy.md`
var __importDefault = (this && this.__importDefault) || function (mod) {
    return (mod && mod.__esModule) ? mod : { "default": mod };
};
Object.defineProperty(exports, "__esModule", { value: true });
const logger_js_1 = __importDefault(require("../lib/logger.js"));
const log = (0, logger_js_1.default)("casa:middleware:strip-proxy-path");
exports.default = ({ mountUrl = "/" }) => [
    (req, res, next) => {
        // TODO:
        // We _may_ have to start tracking the various prefix in order to differentiate
        // between a proxy prefix, and a parent app's path.
        // Assume everything before `mountUrl` is the proxy path prefix and remove it
        req.originalBaseUrl = req.originalBaseUrl ?? req.baseUrl;
        req.baseUrl = mountUrl.replace(/\/$/, "");
        // If the app has been mounted directly on the specific `mountUrl`, then
        // there's nothing we need to do and can let this request pass-through.
        if (req.baseUrl === req.originalBaseUrl) {
            next();
        }
        else if (req.__CASA_BASE_URL_REWRITTEN__) {
            delete req.__CASA_BASE_URL_REWRITTEN__;
            next();
        }
        else {
            // Strip the proxy path prefix from the original URL so that
            // subsequent middleware sees the URL path as though proxy wasn't there.
            // req.url will already have the proxy prefix and mountUrl removed.
            /* eslint-disable security/detect-non-literal-regexp */
            log.trace(`req.originalUrl before proxy stripping: ${req.originalUrl}`);
            req.originalUrl = req.originalUrl.replace(new RegExp(`^/.+?${mountUrl}`), mountUrl);
            log.trace(`req.originalUrl after proxy stripping: ${req.originalUrl}`);
            /* eslint-enable security/detect-non-literal-regexp */
            // Issuing this call will re-run this same middleware, so we use this
            // `__CASA_BASE_URL_REWRITTEN__` flag to prevent recursion.
            req.__CASA_BASE_URL_REWRITTEN__ = true;
            req.app.handle(req, res, next);
        }
    },
];
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