php 实现图片下载

1.控制器
public function downPic(){
    $filename = input('file','','string');    //文件所在路径
    // 检查文件是否存在
    if (! file_exists($filename) ) {
        $this->error('文件未找到');
    }else{
        $fileinfo = pathinfo($filename);
        header('Content-type: application/x-' . $fileinfo['extension']);
        header('Content-Disposition: attachment; filename=' . $fileinfo['basename']);
        readfile($filename);
        exit();
    }
}
2.html中，js直接访问，或者直接用href链接

function downPic() {
  var pic = $('#show_pic').attr('src');
  window.location.href = "{:url('/home/downPic')}"+'?file='+pic;   
}