问题描述

我是一名 PHP 初学者，目前正在学习验证文件上传"部分.

I'm a PHP beginner and currently learning the "Validating the File Upload" part.

我做了一个包含以下代码的 test.php 页面:

I made a test.php page containing following code:

var_dump(@$_FILES['file']['type']);

首先，我上传了一张图片img.gif"并返回:

First, I uploaded an image "img.gif" and it returned:

string 'image/gif' (length=9)

然后，我将图像的扩展名更改为.jpg"并返回:

Then, I changed the image's extension to ".jpg" and it returned:

string 'image/jpeg' (length=10)

所以我意识到 $_FILES["file"]["type"] 只返回上传的文件扩展名，但实际上并没有检查它是什么文件.

So I realized $_FILES["file"]["type"] only return the uploaded file extension but didn't actually check what file is it.

在这个页面，http://www.w3schools.com/php/php_file_upload.asp，有是代码:

In this page, http://www.w3schools.com/php/php_file_upload.asp, there is a code:

$allowedExts = array("gif", "jpeg", "jpg", "png");
$extension = end(explode(".", $_FILES["file"]["name"]));
if ((($_FILES["file"]["type"] == "image/gif")
|| ($_FILES["file"]["type"] == "image/jpeg")
|| ($_FILES["file"]["type"] == "image/jpg")
|| ($_FILES["file"]["type"] == "image/png"))
&& ($_FILES["file"]["size"] < 20000)
&& in_array($extension, $allowedExts))

我想知道为什么上面的代码会检查文件扩展名两次?我从上面的代码中删除了一些，这是我的新代码:

I'm wondering why above codes check file extension twice? I deleted some from above codes and this is my new code:

$allowedExts = array("gif", "jpeg", "jpg", "png");
$extension = end(explode(".", $_FILES["file"]["name"]));
if (($_FILES["file"]["size"] < 20000) && in_array($extension, $allowedExts))

我的代码正确吗?或者你有什么更好的方法来验证上传的文件是图片吗?

Is my code correct? Or do you have any better ways to validate the upload file is a image?

谢谢！

推荐答案

您应该将文件的 tmp_name* 传递给 getimagesize，它会给你图片的大小和类型(如果是图片).如果传递的参数是文件而不是图像，则返回 false，这将允许您进行验证.

You should pass the tmp_name of the file* to getimagesize, it will give you the size and type of the image (if it is an image). If the passed argument is a file but not an image it returns false, that will allow you to validate.

图像验证唯一可靠的方法是使用 GD 或 Imagick 制作它的副本 - getimagesize 很容易被黑.

The only reliable method of image validation is to make a copy of it using GD or Imagick - getimagesize can be easily hacked.

*:我的意思是上传后创建的临时文件.

*: I mean, the temporal file created after upload.

例如:

if ($_SERVER['REQUEST_METHOD'] === 'POST')
{
    $file = $_FILES['file']['tmp_name'];
    if (file_exists($file))
    {
        $imagesizedata = getimagesize($file);
        if ($imagesizedata === FALSE)
        {
            //not image
        }
        else
        {
            //image
            //use $imagesizedata to get extra info
        }
    }
    else
    {
        //not file
    }
}

此代码使用 file_exists 只是为了通用.如果没有上传文件，您将获得 $_FILES['file']['size'] = 0, $_FILES['file']['tmp_name'] = '' 和 $_FILES['file']['error'] = 4.另请参阅is_readable.有关错误值，请参阅 文件上传错误解释，位于 php.net.

This code uses file_exists just to be general. In case no file were uploaded you would get $_FILES['file']['size'] = 0, $_FILES['file']['tmp_name'] = '' and $_FILES['file']['error'] = 4. See also is_readable. For the error values see file upload errors explained at php.net.

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