Checking File Mime Type
<?php //$file = $_FILES['upload']['tmp_name']; $file = 'uploads/image.png'; $mtype = mime_content_type($file); echo $mtype; // image/png
Checking a file type by using the $_FILES['upload']['type'] is not a reliable way. It returns mime type based on the file extension, for example, if the file extension is png it returns ‘image/png’ and if the file extension is txt it returns ‘text/plain’.
In the above example, we are using the mime_content_type function to load the actual content type of a file (from the magic.mime file on your PHP server) regardless of its extension.
Example: Creating a function to validate file mime type
<?php
// ... ...
$file = $_FILES['upload']['tmp_name'];
$error = isValidMimeType( $file ) ;
if ($error === false)
echo 'File is valid';
else
echo $error;
function isValidMimeType($file){
$types = ['image/jpeg','image/gif','image/png'];
$type = mime_content_type($file);
if ( in_array($type, $types) )
return false;
return 'Error: Only '. implode (', ', $types). ' are allowed';
}
Checking file extension
To determine if a file is potentially unsafe, you need to extract the filename extension. You can do that with the pathinfo() function:
<?php
//$file = $_FILES['upload']['name'];
$file = '/usr/etc/info.inc.php';
$info = pathinfo($file);
echo $info['extension']; // prints: php
print_r($info);
/* Prints: Array
(
[dirname] => /usr/etc
[basename] => info.inc.php
[extension] => php
[filename] => info.inc
)*/
The PHP pathinfo() function returns information about a file path (including the file extension). By default it returns an associative array with the following keys:
- dirname: directory that contains the file
- basename: file name including extension
- extension: file extension
- filename: file name without extension
Example: Creating a function to restrict (or allow multiple) file extensions
<?php
//$filename = $_FILES['upload']['name'];
$filename = 'system.exe';
$error = isValidExtension ($filename);
if ($error === false)
echo 'Valid file extension';
else
echo $error;
function isValidExtension($file) {
$exts = ['gif', 'png', 'jpg'];
$info = pathinfo($file);
if (in_array($info['extension'], $exts))
return false;
return 'Error: Only '. implode (', ', $exts). ' are allowed';
}
The above code outputs “Error: Only gif, png, jpg are allowed” on the screen.
Processing Forms in PHP: