PHP引入endroid/qr-code类库生成指定二维码

<?php
namespace app\subsite\controller;
use Endroid\QrCode\QrCode;
class Index extends Base
{
    function _initialize()
    {
        parent::_initialize();
    }
    /*
     * 生成二维码图片
     */
    public function qr_code()
    {
        $link = 'http://'.$_SERVER['HTTP_HOST'].'/subsite/index/register';
        $sha1 = sha1($link);
        $qrcode_dir = dce_dir_root . '/qrcode/' . substr($sha1, 0, 2)  .'/'. substr($sha1, 2, 3) . '/';
        if (!file_exists($qrcode_dir)) mkdir($qrcode_dir, 0777, true);
        $file_name = $qrcode_dir .$sha1 . '.png';
        header('Content-Type: image/png');
        if (is_file($file_name)) {
            echo file_get_contents($file_name);
        } else {
            $qrCode = new QrCode($link);
            echo $qrCode->writeString();
            $qrCode->writeFile($file_name);
        }
        die();
    }
}