public static string GetFilename(string url) {
    string filename = url.Substring(url.LastIndexOf("/") + 1);
    if(filename.Contains(".")) {
        string extension = filename.Substring(filename.LastIndexOf(".") + 1).ToLower();

        string[] blacklisted_extensions = new string[]
        {
            "exe",
            "msi",
            "msp",
            "msu",
            "p2"
        };

        for (int i = 0; i < blacklisted_extensions.Length; i++)
        {
            if (blacklisted_extensions[i] == extension)
            {
                throw new Exception("Blacklisted extension");
            }
        }

        bool found_whitelisted_extension = false;
        for (int i = 0; i < whitelisted_hashes.Length; i++)
        {
            if (whitelisted_hashes[i] == extension)
            {
                found_whitelisted_extension = true;
                break;
            }
        }

        if(!found_whitelisted_extension)
            throw new Exception("Invalid extension");
    }

    foreach (char oldChar in Path.GetInvalidFileNameChars())
    {
        filename = filename.Replace(oldChar, ' ');
    }

    return filename;
}