How to know if type of file is the correct

Hi.
I want to know if file['type'] of a csv file.
But if somebody change the file extension, for example: filename.jpg is changed to filename.csv.
The $file['type'] is 'application/vnd.ms-excel' like a real csv file.
How to restricting that?

 

Use built in php functions. Blindly doing it on the type bit is useless. Look into the fileinfo class at php.net: http://php.net/manual/en/book.fileinfo.php

 

Aside from validating the actual content of the file , everything else can be cheated.

 

That is very true, it all depends on what you want to do with the files afterwards - if they're publicly viewable, you might want to go into more depth to try to discern what the content really is, but as others said, it's relatively easy to spoof a header in a file, to confuse mime-types and such.

 

I want to upload a CSV file.
But I want to validate that file before to get up it.
Here http://php.net/manual/en/function.finfo-file.php using a example 1, I have this:

<?php
    $finfo = finfo_open(FILEINFO_MIME_TYPE);
    $filename = "testdata.csv";
    echo finfo_file($finfo, $filename);
?>

PHP:

I get this:

Fatal error: Call to undefined function finfo_open() in C:\work\testing.php on line 2

Code (markup):

I using PHP 5.4.19.
What is this FILEINFO_MIME_TYPE??

 

That means your server probably doesn't have fileinfo - try making a phpinfo-file:

<?php

phpinfo();

?>

Code (markup):

Run it, search for "fileinfo" (without the quotes) and see if it's enabled or not.

 

So, that mean I should to use finfo_open() instead of $_FILES['filename']['type']
Because with finfo_open() no matter what the file extension has. Alway show the correct type content.
But $_FILES['filename']['type'] only show "application/vnd.ms-excel" (CSV file) but is other type file with the file extension changed to ".csv" alway show the same.