How to get the content-type of a file in PHP?

Question

I'm using PHP to send an email with an attachment. The attachment could be any of several different file types (pdf, txt, doc, swf, etc).

First, the script gets the file using "file_get_contents".

Later, the script echoes in the header:

Content-Type: <?php echo $the_content_type; ?>; name="<?php echo $the_file_name; ?>"

How to I set the correct value for $the_content_type?

Answer 1

I am using this function, which includes several fallbacks to compensate for older versions of PHP or simply bad results:

function getFileMimeType($file) {
    if (function_exists('finfo_file')) {
        $finfo = finfo_open(FILEINFO_MIME_TYPE);
        $type = finfo_file($finfo, $file);
        finfo_close($finfo);
    } else {
        require_once 'upgradephp/ext/mime.php';
        $type = mime_content_type($file);
    }

    if (!$type || in_array($type, array('application/octet-stream', 'text/plain'))) {
        $secondOpinion = exec('file -b --mime-type ' . escapeshellarg($file), $foo, $returnCode);
        if ($returnCode === 0 && $secondOpinion) {
            $type = $secondOpinion;
        }
    }

    if (!$type || in_array($type, array('application/octet-stream', 'text/plain'))) {
        require_once 'upgradephp/ext/mime.php';
        $exifImageType = exif_imagetype($file);
        if ($exifImageType !== false) {
            $type = image_type_to_mime_type($exifImageType);
        }
    }

    return $type;
}

It tries to use the newer PHP finfo functions. If those aren't available, it uses the mime_content_type alternative and includes the drop-in replacement from the Upgrade.php library to make sure this exists. If those didn't return anything useful, it'll try the OS' file command. AFAIK that's only available on *NIX systems, you may want to change that or get rid of it if you plan to use this on Windows. If nothing worked, it tries exif_imagetype as fallback for images only.

I have come to notice that different servers vary widely in their support for the mime type functions, and that the Upgrade.php mime_content_type replacement is far from perfect. The limited exif_imagetype functions, both the original and the Upgrade.php replacement, are working pretty reliably though. If you're only concerned about images, you may only want to use this last one.