PHP で電子メール添付ファイルのコンテンツ タイプを判断する方法

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

    // Check for unreliable results
    if (!$type || in_array($type, array('application/octet-stream', 'text/plain'))) {
        // Try file command (only available on *NIX systems)
        $secondOpinion = exec('file -b --mime-type ' . escapeshellarg($file), $foo, $returnCode);
        if ($returnCode === 0 && $secondOpinion) {
            $type = $secondOpinion;
        }
    }

    // Try exif_imagetype for images
    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;
}

$the_content_type = getFileMimeType($filepath);