Using WordPress ‘check_upload_mimes()’ PHP function

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The check_upload_mimes() WordPress PHP function cross-verifies an array of MIME types against a predefined list of approved types. WordPress has its own set of acceptable upload file types, which is defined in the wp-includes/functions.php file under the function get_allowed_mime_types(). check_upload_mimes() filters this list according to the file types authorized by Multisite Super Admins at wp-admin/network/settings.php.

Usage

Let’s take an example where you have an array of MIME types and you want to verify them against the allowed list. Here’s a brief code snippet showcasing this:

$mimes = array( 
  'jpg|jpeg|jpe' => 'image/jpeg', 
  'php' => 'application/x-php', // This isn't on the whitelist!
); 

$mimes = check_upload_mimes($mimes); 
print_r($mimes);

In this case, the output will be:

Array(
  'jpg|jpeg|jpe' => 'image/jpeg'
)

Parameters

  • $mimes (array) (required): This is the array of MIME types you want to check.

More information

For more details, refer to the WordPress Developer Resources: check_upload_mimes()

Examples

Filtering an Array of MIME Types

If you have an array of MIME types and you want to filter them against the allowed list, you can use the check_upload_mimes() function.

// Define your MIME types array
$mimes = array(
  'gif' => 'image/gif',
  'png' => 'image/png',
  'svg' => 'image/svg+xml',
  'doc' => 'application/msword',
  'exe' => 'application/x-msdownload' // Not allowed!
);

// Check against the allowed types
$mimes = check_upload_mimes($mimes);

// Print the filtered array
print_r($mimes);

This will output:

Array(
  'gif' => 'image/gif',
  'png' => 'image/png',
  'svg' => 'image/svg+xml',
  'doc' => 'application/msword'
)

Checking a Single MIME Type

If you only want to check a single MIME type, you can simply create an array with a single element.

// Define your MIME type
$mimes = array(
  'mp3' => 'audio/mpeg'
);

// Check against the allowed types
$mimes = check_upload_mimes($mimes);

// Print the result
print_r($mimes);

This will output:

Array(
  'mp3' => 'audio/mpeg'
)

Checking Non-Image MIME Types

You can use check_upload_mimes() to check non-image MIME types as well.

// Define your MIME types array
$mimes = array(
  'pdf' => 'application/pdf',
  'xls' => 'application/vnd.ms-excel',
  'psd' => 'image/vnd.adobe.photoshop',
  'ai' => 'application/postscript'
);

// Check against the allowed types
$mimes = check_upload_mimes($mimes);

// Print the filtered array
print_r($mimes);

This will output:

Array(
  'pdf' => 'application/pdf',
  'xls' => 'application/vnd.ms-excel',
  'psd' => 'image/vnd.adobe.photoshop',
  'ai' => 'application/postscript'
)

Checking Multiple Image MIME Types

You can also use check_upload_mimes() to verify multiple image MIME types.

// Define your MIME types array
$mimes = array(
  'jpg' => 'image/jpeg',
  'png' => 'image/png',
  'gif' => 'image/gif',
  'ico' => 'image/x-icon',
  'bmp' => 'image/bmp',
  'tiff' => 'image/tiff'
);

// Check against the allowed types
$mimes = check_upload_mimes($mimes);

// Print the filtered array
print_r($mimes);

This will output:

Array(
  'jpg' => 'image/jpeg',
  'png' => 'image/png',
  'gif' => 'image/gif',
  'ico' => 'image/x-icon',
  'bmp' => 'image/bmp',
  'tiff' => 'image/tiff'
)

Checking Non-Allowed MIME Types

Let’s see what happens when you check MIME types that are not on the allowed list.

// Define your MIME types array
$mimes = array(
  'exe' => 'application/x-msdownload', // Not allowed!
  'bat' => 'application/x-msdos-program' // Not allowed!
);

// Check against the allowed types
$mimes = check_upload_mimes($mimes);

// Print the filtered array
print_r($mimes);

As expected, this will output an empty array, as none of the MIME types are on the allowed list.

Array()