curl 向远程服务器传输file文件

public function upload(){
    //获取上传文件信息，文件名称以自己实际上传文件名称为准
    $fileinfo = $_FILE['filename'];

    //请求参数，依据商户自己的参数为准
    $requestParam['version'] = '';
    $requestParam['cmd_id'] = '';
    $requestParam['mer_cust_id'] = '';
    $requestParam['attach_file'] = new \CURLFile($fileinfo['tmp_name'],$fileinfo['type'],$fileinfo['name']);

    //发起请求
    $param = [
        'requestData'  => [
            'cmd_id' => $requestParam['cmd_id'],
            'mer_cust_id' => $requestParam['mer_cust_id'],
            'version' => $requestParam['version'],
            'attach_file' => $requestParam['attach_file'],
        ],
        'headers' => ['Content-type' => 'multipart/form-data;charset=UTF-8']
    ];

    $is_upload = ;
    $requestRes = $this->request($param,$is_upload);

    return $requestRes ;

}

private function request($param, $is_upload=) {
    // 请求接口所以参数初始化
    $data = [
        'url' => $this->apiUrl, // 接口 url
        'requestData' => $is_upload ? $param['requestData'] : http_build_query($param['requestData']), // 请求接口参数
        'headers' => $param['headers']
    ];

    //print_r($data); //debug 打印接口传输数据

    $res = $this->httpPostRequest($data['url'], $data['headers'], $data['requestData']);

    if (empty($res) || $res['info']['http_code'] != '') {
        $this->json_ret('','http request error',[$res['error']]);
    }

    return [
        'status' => $res['info']['http_code'],
        'body' => $res['body']
    ];
}

//curl post 请求
private function httpPostRequest($url = '', $header = array(), $requestData = array()) {
    $curl = curl_init();
    curl_setopt($curl, CURLOPT_HTTPHEADER, $header);
    curl_setopt($curl, CURLOPT_URL, $url);
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($curl, CURLOPT_POST, true);
    curl_setopt($curl, CURLOPT_POSTFIELDS, $requestData);
    $res = curl_exec($curl);
    $info = curl_getinfo($curl);
    $error = curl_error($curl);
    curl_close($curl);

    return [
        'body' => $res,
        'info' => $info,
        'error' => $error,
    ];
}