来自MySQL C＃/ PHP的流文件

Question

I'm working on a Client Application where my user authenticate against a web API made in PHP. When my user is authenticated I want to stream a blob from the MyBB database, so I can use Assembly.Load on my client and run the .exe file.

This is how I'm trying to achieve this. This is my API on the server

global $db, $encryptionEngine;
if (isset($_GET['file']) && isset($_GET['username'])) 
{
    $username = $encryptionEngine->init($_GET['username'],"decrypt");
    $query = $db->simple_select("users", "*", "LOWER(username)='".$db->escape_string(my_strtolower($username))."'", array('limit' => 1));
    $user = $db->fetch_array($query);

    if ($user['usergroup'] == 3 || $user['usergroup'] == 4 || $user['usergroup'] == 6 || $user['usergroup'] == 8 || $user['usergroup'] == 9)
    {

        $filename = $encryptionEngine->init($_GET['file'],"decrypt");
        $query = $db->simple_select("files", "filecontent", "LOWER(filename)='".$db->escape_string(my_strtolower($filename))."'", array('limit' => 1));
        $file = $db->fetch_array($query);
        return $file['filecontent'];
    }
}

filecontent on my MySQL database is the Byte[] or VarBinary. And this how I try too stream the file in my Client(C#)

        public byte[] StreamFile(string file, string username)
    {
        using (WebClient webClient = new WebClient())
        {
            string address = Conversions.ToString(_authUrl + "?action=streamFile&file=" + _encryption.Encrypt(file) +"&username="+_encryption.Encrypt(username));
            byte[] str = webClient.DownloadData(address);
            return str;
        }
    }

How ever, as I'm using webClient.DownloadData it will download the whole page as a byte[] but how can I just access the VarBinary / Byte[] ?