php使用mongo的GridFS存储文件

<?php
    //php使用mongo的GridFS存储文件
    $conn = new MongoClient();
    $db = $conn->photos;
    $collection = $db->getGridFS();

    //存储文件
    $id = $collection->storeFile('./logo22.png');

    //存储文件二进制流
//    $data = file_get_contents('./logo22.png');
//    $id = $collection->storeBytes($data,array('param'=>'logo图片'));

    //保存
    //$id = $collection->storeUpload('upfile');
    //相当于
    //$id = $collection->storeFile($_FILES['upfile']['tmp_name']);

    //读取
    $logo = $collection->findOne(array('_id'=>$id));
    header('Content-type:image/png');//输出图片头
    //var_dump($logo);
    echo $logo->getBytes();