Proper Way To Validate MIME Type Of Files While Handling File Uploads In PHP

In this article, I will show you a cool tip on how to properly validate the file MIME types even if they change the extension of the file.

I will cover the following in this article

1. Basic HTML Form
2. General Old Way Validation (Probably Wrong Way)
3. The Right Way To Validate MIME Type ( finfo )
4. Different MIME Extensions Link

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Prerequisites

Basic knowledge on PHP. Even if you don't know how to upload the files and handle it then I have written an article on it:

How To Uploads Files In PHP?

How To Upload Image In PHP?

---

1) Basic HTML Form

This is very basic HTML form make sure you have enctype="multipart/form-data"

<form action="store_product.php" method="post" enctype="multipart/form-data">
    <div>
        <input type="file" name="product_invoice" id="product_invoice">
    </div> <br>
    <div>
        <input type="submit" value="Create Product">
    </div>
</form>

---

2) General Old Way Validation (Probably Wrong Way)

From the above form when you select the image and upload it will go to store_product.php PHP file which will handle the file upload with validation.

Following is the snippet code which demonstrates the file validation

/** Store the file details in variable */
$product_invoice    = $_FILES['product_invoice'];

/** Uploaded file name */
$file_name          = $product_invoice['name'];
$file_tmp           = $product_invoice['tmp_name'];

/** Using pathinfo() to get the file extension of file */
$pathinfo           = pathinfo($file_name);
$extension          = $pathinfo['extension'];

/** Allowed extensions */
$file_extensions    = ['pdf', 'xls', 'jpeg', 'jpg', 'png', 'svg', 'webp'];

/** Check File extensions */
if(!in_array($extensio
n, $file_extensions)){
    $errors[] = 'File allowed extensions '. implode(', ', $file_extensions);
}

The above is wrong because we are validating based on file extension. Because someone may upload video & change just the extension to jpeg or pdf.

---

3) The Right Way To Validate MIME Type ( finfo )

To properly validate the file MIME you need to use finfo which internally uses finfo_open

Basically you use it the following way

/** Using finfo to just get the MIME type */
$finfo      = new finfo(FILEINFO_MIME_TYPE);

/** You will get extension along with the mime types */
$extension  = $finfo->file($file_tmp);

Full detailed on the same as follows

/** Store the file details in variable */
$product_invoice    = $_FILES['product_invoice'];

/** Uploaded file name */
$file_name          = $product_invoice['name'];
$file_tmp           = $product_invoice['tmp_name'];

/** Allowed MIME extensions */
$file_extensions    = ['image/jpeg', 'image/pjpeg', 'application/pdf'];

/** Using finfo to just get the MIME type */
$finfo      = new finfo(FILEINFO_MIME_TYPE);

/** You will get extension along with the mime types */
$extension  = $finfo->file($file_tmp);

/** Check File extensions */
if(!in_array($extension, $file_extensions)){
    $errors[] = 'File allowed extensions '. implode(', ', $file_extensions);
}

---

4) Diff MIME Extensions Link

I don't want to reinvent the wheel. So here is the link for the CODEIGNITER FRAMEWORK MIME TYPES

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Conclusion

Hope you liked the article. If yes then please do share with your friends.

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