loopback/lib/express-middleware.js

var express = require('express');
var path = require('path');

var middlewares = exports;

function safeRequire(m) {
  try {
    return require(m);
  } catch (err) {
    return undefined;
  }
}

function createMiddlewareNotInstalled(memberName, moduleName) {
  return function () {
    var msg = 'The middleware loopback.' + memberName + ' is not installed.\n' +
      'Run `npm install --save ' + moduleName + '` to fix the problem.';
    throw new Error(msg);
  };
}

var middlewareModules = {
  "compress": "compression",
  "timeout": "connect-timeout",
  "cookieParser": "cookie-parser",
  "cookieSession": "cookie-session",
  "csrf": "csurf",
  "errorHandler": "errorhandler",
  "session": "express-session",
  "methodOverride": "method-override",
  "logger": "morgan",
  "responseTime": "response-time",
  "favicon": "serve-favicon",
  "directory": "serve-index",
  // "static": "serve-static",
  "vhost": "vhost"
};

middlewares.bodyParser = safeRequire('body-parser');
middlewares.json = middlewares.bodyParser && middlewares.bodyParser.json;
middlewares.urlencoded = middlewares.bodyParser && middlewares.bodyParser.urlencoded;

for (var m in middlewareModules) {
  var moduleName = middlewareModules[m];
  middlewares[m] = safeRequire(moduleName) || createMiddlewareNotInstalled(m, moduleName);
}

// serve-favicon requires a path
var favicon = middlewares.favicon;
middlewares.favicon = function (icon, options) {
  icon = icon || path.join(__dirname, '../favicon.ico');
  return favicon(icon, options);
};