COAP library crashes when it receives two confimable responses with the same messageId & token

crash-append-nonobservable.js

/*
 * Copyright (c) 2013-2015 node-coap contributors.
 *
 * node-coap is licensed under an MIT +no-false-attribs license.
 * All rights not explicitly granted in the MIT license are reserved.
 * See the included LICENSE file for more details.
 */

var coap      = require('../../')
  , parse     = require('coap-packet').parse
  , generate  = require('coap-packet').generate
  , dgram     = require('dgram')
  , bl        = require('bl')
  , sinon     = require('sinon')
  , request   = coap.request

describe('request', function() {
  var server
    , server2
    , port

  beforeEach(function (done) {
    port = nextPort()
    server = dgram.createSocket('udp4')
    server.bind(port, done)
  })

  afterEach(function () {
    server.close()

    if (server2)
      server2.close()

    server = server2 = null
  })

  function ackBack(msg, rsinfo) {
    var packet = parse(msg)
      , toSend = generate({
        messageId: packet.messageId
        , ack: true
        , code: '0.00'
      })
    server.send(toSend, 0, toSend.length, rsinfo.port, rsinfo.address)
  }

  it('should not crash with a response with a delayed CON message and same messageId & token', function (done) {
    var req = request({
      port: port
      , confirmable: true
    })

    server.once('message', function (msg, rsinfo) {
      var packet = parse(msg)
        , toSend = generate({
          token: packet.token
          , messageId: packet.messageId
          , payload: new Buffer('42')
          , confirmable: true
          , code: '2.00'
        })
      server.send(toSend, 0, toSend.length, rsinfo.port, rsinfo.address)

      toSend = generate({
        token: packet.token
        , messageId: packet.messageId
        , payload: new Buffer('42')
        , confirmable: true
        , code: '2.00'
      })
      server.send(toSend, 0, toSend.length, rsinfo.port, rsinfo.address)
    })

    req.on('response', function (res) {
      res.pipe(bl(function (err, data) {
        expect(data).to.eql(new Buffer('42'))
        done()
      }))
    })

    req.end()
  })
})