如何在同一套接字上发送消息和接收响应

本文关键字：消息 响应 套接字 | 更新日期: 2023-09-27 18:25:38

我有以下代码，它发送多播消息，然后等待将响应发送到消息来源的地址。如果我观察Wireshark中的流量，我可以看到消息发送正常，响应返回到正确的IP和端口，但套接字从未从接收线路返回，就像没有收到响应一样。

    var multicastAddress = IPAddress.Parse("239.255.255.250");
    var multicastPort = 1900;
    var unicastPort = 1901;        
    using (var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp))
    {
        socket.Bind(new IPEndPoint(IPAddress.Any, unicastPort));
        socket.Connect(new IPEndPoint(multicastAddress, multicastPort));
        var thd = new Thread(() =>
             {
                 try
                 {
                     while (true)
                     {
                         var response = new byte[8000];
                         EndPoint ep = new IPEndPoint(IPAddress.Any, unicastPort);
                         socket.ReceiveFrom(response, ref ep);
                         var str = Encoding.UTF8.GetString(response);
                         Devices.Add(new SsdpDevice() {Location = str});
                     }
                 }
                 catch
                 {
                     //TODO handle exception for when connection closes
                 }
             });
        socket.Send(broadcastMessage, 0, broadcastMessage.Length, SocketFlags.None);
        thd.Start();
        Thread.Sleep(30000);
        socket.Close();
    }

我知道我应该在socket类上使用异步方法，并且需要停止依赖Thread.Sleep，但我只想在整理代码之前先用一个简单的例子。

如何在同一套接字上发送消息和接收响应

Gavin，看看这个：

  • 不要使用不同的端口。您希望如何在一个上进行多播并在另一个上接收
  • 不要使用Connect()，多播是无连接的消息传递（就像广播一样）
  • 将套接字选项设置为Bind()之后的多播
  • 使用SendTo()而不是Send()，这在这种情况下是不起作用的
  • 首先开始接收（即使在阻塞模式下，它也是不同的端点），然后发送

还有一个简单的工作示例：

var broadcastMessage = Encoding.UTF8.GetBytes("Hello multicast!");
var multicastAddress = IPAddress.Parse("239.255.255.250");
var signal = new ManualResetEvent(false);
var multicastPort = 1900;
using (var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp))
{
    var multicastEp = new IPEndPoint(multicastAddress, multicastPort);
    EndPoint localEp = new IPEndPoint(IPAddress.Any, multicastPort);
    // Might want to set this:
    //socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, 1); 
    socket.Bind(localEp);
    socket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(multicastAddress, IPAddress.Any));
    // May want to set this:
    //socket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.MulticastTimeToLive, 0); // only LAN
    var thd = new Thread(() =>
        {
            var response = new byte[8000];
            socket.ReceiveFrom(response, ref localEp);
            var str = Encoding.UTF8.GetString(response).TrimEnd(''0');
            Console.WriteLine("[RECV] {0}", str);
            signal.Set();
            Console.WriteLine("Receiver terminating...");
        });
    signal.Reset();
    thd.Start();
    socket.SendTo(broadcastMessage, 0, broadcastMessage.Length, SocketFlags.None, multicastEp);
    Console.WriteLine("[SEND] {0}", Encoding.UTF8.GetString(broadcastMessage));
    signal.WaitOne();
    Console.WriteLine("Multicaster terminating...");
    socket.Close();
    Console.WriteLine("Press any key.");
    Console.ReadKey();
}
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