Crawl express 4.x application to build middleware structure and route mappings.

crawl.js

'use strict';

/**
 * In order for this to work correctly, `this.path = path;` needs to be added in
 * the Layer constructor function here:
 * https://github.com/visionmedia/express/blob/7df7f7a575df4cf26c1d43535a6a1a6b8778933c/lib/router/layer.js#L21
 */

module.exports = function crawl(obj, path, tree) {
    path = path || '';
    tree = tree || {};

    if (obj._router) {

        // obj is application
        path = path || obj.get('mountpath');
        crawl(obj._router, path, tree);

    } else if (Array.isArray(obj.stack)) {

        // obj is application or Route
        // both have the `stack` property
        obj.stack.forEach(function (handler) {
            crawl(handler, path, tree);
        });

    } else if (typeof obj.stack === 'function') {

        // TODO: Is this really a thing still?
        crawl(obj.stack, path, tree);

    } else if (obj.route) {

        // obj is Layer
        // obj.route is Route, which has the necessary `path` property.
        crawl(obj.route, path + (obj.route.path || ''), tree);

    } else if (obj.handle) {

        // obj is either a Layer or a special object. TBD

        if (obj.method) {

            // Special object in express/lib/router/route.js
            // @see https://github.com/visionmedia/express/blob/4638883f0d943b551c60862161e1488e9c150297/lib/router/route.js#L164
            path = path || '(all)';

            if (path[path.length - 1] === '/') {
                path = path.slice(0, -1);
            }

            path = path || '/';

            tree[path] = tree[path] || {};
            tree[path][obj.method] = tree[path][obj.method] || [];
            tree[path][obj.method].push(obj.handle.name || '(anonymous)');

        } else {

            // obj is Layer or special object (still)
            // @see https://github.com/visionmedia/express/blob/4638883f0d943b551c60862161e1488e9c150297/lib/router/route.js#L140

            if (obj.path) {
                // It's a Layer
                path += obj.path;
            }

            // obj.handle is Function
            crawl(obj.handle, path, tree);

        }

    } else {

        path = path || '(all)';
        tree[path] = tree[path] || [];
        tree[path].push(obj.name || '(anonymous)');

    }

    return tree;
};