问stream_copy_to_stream()总是返回0

EN

private function upload_file($file_name, $tmp_name)
{
    $result = array(
            'is_successful' => true,
            'extra_message' => ''
        );

    $target_path = $this->get_target_file_path($file_name, $tmp_name);
    move_uploaded_file($tmp_name, $target_path);
    $result['is_successful'] = $this->handle_upload_request($target_path);
    if ( $result['is_successful'] ) {
        $result['extra_message'] = $target_path;
    } else {
        $result['extra_message'] = 'Unknown error occured.<br />';
    }

    return $result;
}

private function handle_upload_request($path)
{
    $input = fopen("php://input", "r");
    $temp = tmpfile();
    $real_size = stream_copy_to_stream($input, $temp);
    fclose($input);

    echo $real_size;
    if ($real_size != $this->get_size()){            
        return false;
    }

    $target = fopen($path, "w");        
    fseek($temp, 0, SEEK_SET);
    stream_copy_to_stream($temp, $target);
    fclose($target);

    return true;
}