Nodejs中使用captchapng模块生成图片验证码

/** * 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);}