how to check the uploaded file type is pdf [duplicate]

Question

Possible Duplicate:
How to check file types of uploaded files in PHP?

I have uploading features on my site and only PDF uploads are allowed. How can I check that the uploaded file is only a PDF? Just like getimagesize() can verify image files. Is there any way to check the file is a PDF? My code is below:

$whitelist = array(".pdf");

foreach ($whitelist as $item) {
    if (preg_match("/$item\$/i", $_FILES['uploadfile']['name'])) {
        
    }
    else {
        redirect_to("index.php");
    }
}

$uploaddir = 'uploads/';

$uploadfile = mysql_prep($uploaddir . basename($_FILES['uploadfile']['name']));

if (move_uploaded_file($_FILES['uploadfile']['tmp_name'], $uploadfile)) {
    echo "succussfully uploaded";
}

Functions redirect_to and mysql_prep are defined by me. But mime type can be changed using headers. So is there any way to check the file to be an original pdf?

Answer 1

Look for the PDF magic number by opening the file and reading the first few bytes of data. Most files have a specific format, and PDF files start with %PDF.

You can check the first 5 characters of the file, if they equal "%PDF-", it is likely a real PDF (however, this does not definitively prove that it is a PDF file, as any file can begin with those 5 characters). The next 4 characters in a proper PDF file contain the version number (i.e. 1.2).