index.js

/**
 * CORS middleware for expressjs
 * Copyright 2013 by Yuriy Bogdanov <chinsay gmail>
 *
 * (MIT LICENSE)
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

module.exports = function(options) {

  options = options || {}
  options.allowedOrigins = options.allowedOrigins || []
  if (!options.hasOwnProperty('allowCredentials')) {
    options.allowCredentials = true  
  }
  options.methods = options.methods || ['GET', 'POST', 'PUT', 'DELETE', 'PATCH', 'OPTIONS']
  options.headers = options.headers || ['X-Requested-With', 'Content-Type']

  // Parse allowed origins list and turn them all into regexps
  var allowedOrigins = options.allowedOrigins.map(function(origin){
    // check if allowed origin starts with http:// or https://
    // of not, then we should allow both
    var anyHttp = !origin.match(/^https?:\/\//)
    // random hash tokens to escape wildcard sequences like "*." and ":*"
    var rand = 'WnqkQwirtbRoerjaSnei20ssbqQi',
        rand1 = rand + '1',
        rand2 = rand + '2'
    // hide wildcard sequences
    origin = origin.replace(/\*\./g, rand1)
    origin = origin.replace(/:\*/g, rand2)
    // escape wildcard regexp characters in origin value
    origin = escapeRegExp(origin)
    // return wildcard sequences back, turning them into reg expressions
    origin = origin.replace(new RegExp(rand1, 'g'), '(.*\\.)?')
    origin = origin.replace(new RegExp(rand2, 'g'), '(:\\d+)?')
    // append http/https expression if we allow both
    if (anyHttp) {
      origin = '^https?:\/\/' + origin + '$'
    }
    else {
      origin = '^' + origin + '$'
    }

    return new RegExp(origin)
  })

  // express middleware
  return function(req, res, next){
    var origin = req.get('Origin'), i, matched = false

    // match against all prepared regexp origins
    for (i = 0; i < allowedOrigins.length; i++) {
      if (allowedOrigins[i].test(origin)) {
        matched = true
        break
      }
    }

    if (!matched) return next()

    res.set('Access-Control-Allow-Origin', origin)

    if (options.methods.length) {
      res.set('Access-Control-Allow-Methods', options.methods.join(', '))
    }
    
    if (options.headers.length) {
      res.set('Access-Control-Allow-Headers', options.headers.join(', '))  
    }

    if (options.maxAge) {
      res.set('Access-Control-Max-Age', options.maxAge)
    }

    if (options.allowCredentials) {
      res.set('Access-Control-Allow-Credentials', 'true')
    }

    if ('OPTIONS' == req.method) return res.send(200)
    next()
  }
}

function escapeRegExp(str) {
  return str.replace(/[\-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g, "\\$&");
}