/**

 * 图片验证码

 * @param req

 * @param res

 * @param next

 */

function randomcodePngController(req , res , next){

  var code = '0123456789';

  var length = 4;

  var randomcode = '';

  for (var i = 0; i < length; i++) {

    randomcode += code[parseInt(Math.random() * 1000) % code.length];

  }

  // 保存到session

  if (null == req.session[sessionConstant.login]) {

    req.session[sessionConstant.login] = {};

  }

  req.session[sessionConstant.login][sessionConstant.randomcode] = randomcode;

  // 输出图片

   var p = new captchapng(80,30,parseInt(randomcode)); // width,height,numeric captcha

  p.color(255, 255, 255, 0); // First color: background (red, green, blue, alpha)

  p.color(80, 80, 80, 255); // Second color: paint (red, green, blue, alpha)

  var img = p.getBase64();

  var imgbase64 = new Buffer(img,'base64');

  res.writeHead(200, {

    'Content-Type': 'image/png'

  });

  res.end(imgbase64);

}