简单解决SL多播授权

SL特定源多播和任意源多播，加入组前，需要获得当前域的9430端口的授权。

请求授权的消息叫“公告”，响应的消息叫“授权”。分别用0和1表示。

公告和身份验证消息的格式如下所示：  

struct SilverlightPolicyMessage 

{ 

 byte[3] header = "SL\0"; 

 byte version = 1; 

 byte messageType = {Announcement: 0, Authorization: 1}; 

 byte[4] messageId; 

 byte[2] port; 

 byte[2] applicationOriginUriLength; 

 byte groupAddressLength; 

 byte[applicationOriginUriLength] applicationOriginUri; 

 byte[groupAddressLength] groupAddress; 

}

如果确认应用程序源URI有权加入申请的多播组，那么把消息类型的第5个字节修改为1，表示通过授权，作为响应数据即可：

以下代码测试通过：

 static UdpClient client = null;
        static void Main(string[] args)
        {
            client = new UdpClient(9430);//SL客户端客户端请求授权时，会向9430端口 验证授权
            client.BeginReceive(ReceiveCallback, null);
            Console.Read();
        }

        static void ReceiveCallback(IAsyncResult result)
        {
            IPEndPoint remoteEP = null;
            byte[] Announcement = client.EndReceive(result, ref remoteEP);//接收到公告

            if (result.IsCompleted)
            {
                Console.WriteLine(remoteEP.Address.ToString() + ":" + remoteEP.Port);
                Announcement[4] = 1;//第5个字节0表示公告，1表示授权。其他数据不变，将消息改为授权作为响应
                client.BeginSend(Announcement, Announcement.Length,remoteEP, SendCallback, null);
                Console.WriteLine("Done");
            }
        }

        static void SendCallback(IAsyncResult Asyncresult)
        {
            client.EndSend(Asyncresult);
            if (Asyncresult.IsCompleted)
            {
                Console.WriteLine("Sended");
            }
        }