如何使用 UDP 广播进行网络发现

在 C# 中做同样的事情非常简单

服务器：

var Server = new UdpClient(8888);
var ResponseData = Encoding.ASCII.GetBytes("SomeResponseData");
while (true)
{
    var ClientEp = new IPEndPoint(IPAddress.Any, 0);
    var ClientRequestData = Server.Receive(ref ClientEp);
    var ClientRequest = Encoding.ASCII.GetString(ClientRequestData);
    Console.WriteLine("Recived {0} from {1}, sending response", ClientRequest, ClientEp.Address.ToString());
    Server.Send(ResponseData, ResponseData.Length, ClientEp);
}

客户：

var Client = new UdpClient();
var RequestData = Encoding.ASCII.GetBytes("SomeRequestData");
var ServerEp = new IPEndPoint(IPAddress.Any, 0);
Client.EnableBroadcast = true;
Client.Send(RequestData, RequestData.Length, new IPEndPoint(IPAddress.Broadcast, 8888));
var ServerResponseData = Client.Receive(ref ServerEp);
var ServerResponse = Encoding.ASCII.GetString(ServerResponseData);
Console.WriteLine("Recived {0} from {1}", ServerResponse, ServerEp.Address.ToString());
Client.Close();

下面是一个不同的无服务器解决方案。我需要让一堆覆盆子小童在网络上相互了解，但不能保证谁会活跃。所以这种方法让每个人都成为客户！完整的库可在 GitHub 上找到（免责声明：我创建），这使得整个过程对于 UWP 应用程序来说非常容易。

https://github.com/mattwood2855/WindowsIotDiscovery

此解决方案假定设备名称是唯一的，并且您希望使用 JSON 字符串作为通信协议，但您可以轻松地发送任何其他格式。此外，在实践中尝试捕获所有;)

一般机制：

发现您的地址

public string IpAddress
{
    get
    {
        var hosts = NetworkInformation.GetHostNames();
        foreach (var host in hosts)
        {
            if (host.Type == HostNameType.Ipv4) return host.DisplayName;    
        }
        return "";
    }
}

设置侦听器

var udpPort = "1234";
var socket = new DatagramSocket();
socket.MessageReceived += ReceivedDiscoveryMessage;
await socket.BindServiceNameAsync(udpPort);`

处理传入数据

async void ReceivedDiscoveryMessage(DatagramSocket socket, DatagramSocketMessageReceivedEventArgs args)
{
    // Get the data from the packet
    var result = args.GetDataStream();
    var resultStream = result.AsStreamForRead();
    using (var reader = new StreamReader(resultStream))
    {
        // Load the raw data into a response object
        var potentialRequestString = await reader.ReadToEndAsync(); 
        // Ignore messages from yourself
        if (args.RemoteAddress.DisplayName == IpAddress) return;        
        // Get the message
        JObject jRequest = JObject.Parse(potentialRequestString);
        // Do stuff with the data
    }
}

发送消息

public async void SendDataMessage(string discoveryMessage)
{
    // Get an output stream to all IPs on the given port
    using (var stream = await socket.GetOutputStreamAsync(new HostName("255.255.255.255"), udpPort))
    {
        // Get a data writing stream
        using (var writer = new DataWriter(stream))
        {
            // Write the string to the stream
            writer.WriteString(discoveryMessage);
            // Commit
            await writer.StoreAsync();
        }
    }
}

这个想法是发送包含您的IP地址和名称的发现消息。然后在接收消息功能中，将 IP 名称对添加到设备列表中。添加一些逻辑以避免重复，并在给定名称的 ip 更改时更新 IP 地址。

作为奖励，您可以让每个设备发送他们知道的设备列表。这允许您通过在发件人知道您时不响应来最小化 udp 流量。您甚至可以让接收器将列表与他们自己的列表进行比较，以发现其他设备。

冗余是UDP的朋友，不能保证数据包会被传送。

我知道

它很旧，但有人可能仍然需要这个......接受的答案很棒，但是在服务器端进行此小调整会更好。

修复了 Ilya Suzdalnitski 评论（锁定在第二个客户端上接收呼叫）：

var responseData = Encoding.ASCII.GetBytes("someData");     
while (true)
{
    var server = new UdpClient(8888);
    var clientEp = new IPEndPoint(IPAddress.Any, 0);
    var clientRequestData = server.Receive(ref clientEp);
    var clientRequest = Encoding.ASCII.GetString(clientRequestData);
    Console.WriteLine($"Recived {clientRequest} from {clientEp.Address}, sending 
    response: {responseData}");
    server.Send(responseData, responseData.Length, clientEp);
    server.Close();
}

因为每次响应后，服务器都会关闭并重新创建，因此它可以无休止地工作而不会锁定。

我有同样的问题，但这对我来说并不容易，因为@rufanov建议的答案。

这里有一些情况我有：

• 由于我的应用程序在具有多个网络接口的计算机中正常运行，因此我遇到了广播消息仅在其中一个适配器中发送的问题。为了解决这种情况，我必须首先获取所有网络适配器列表，然后逐个发送广播消息并接收应答消息。
请务必
• 将正确的 localIpEndPoint 绑定到适配器的 IP 地址，否则发送时广播地址将出现问题。

经过一些研究和工作，我得到了这个解决方案。此代码对应于服务器端，并将通过网络发现所有应答 braodcast 消息的设备。

public static void SNCT_SendBroadcast(out List<MyDevice> DevicesList)
{
  DevicesList = new List<MyDevice>();
  byte[] data = new byte[2]; //broadcast data
  data[0] = 0x0A;
  data[1] = 0x60;
  IPEndPoint ip = new IPEndPoint(IPAddress.Broadcast, 45000); //braodcast IP address, and corresponding port
  NetworkInterface[] nics = System.Net.NetworkInformation.NetworkInterface.GetAllNetworkInterfaces(); //get all network interfaces of the computer
  foreach (NetworkInterface adapter in nics)
  {
    // Only select interfaces that are Ethernet type and support IPv4 (important to minimize waiting time)
    if (adapter.NetworkInterfaceType != NetworkInterfaceType.Ethernet) { continue; }
    if (adapter.Supports(NetworkInterfaceComponent.IPv4) == false) { continue; }
    try
    {
        IPInterfaceProperties adapterProperties = adapter.GetIPProperties();    
        foreach (var ua in adapterProperties.UnicastAddresses)
        {
            if (ua.Address.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)
            {
             //SEND BROADCAST IN THE ADAPTER
                //1) Set the socket as UDP Client
                Socket bcSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp); //broadcast socket
                //2) Set socker options
                bcSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.Broadcast, 1);
                bcSocket.ReceiveTimeout = 200; //receive timout 200ms
                //3) Bind to the current selected adapter
                IPEndPoint myLocalEndPoint = new IPEndPoint(ua.Address, 45000);
                bcSocket.Bind(myLocalEndPoint);
                //4) Send the broadcast data
                bcSocket.SendTo(data, ip);
            //RECEIVE BROADCAST IN THE ADAPTER
                int BUFFER_SIZE_ANSWER = 1024;
                byte[] bufferAnswer = new byte[BUFFER_SIZE_ANSWER];
                do
                {
                    try
                    {
                        bcSocket.Receive(bufferAnswer);
                        DevicesList.Add(GetMyDevice(bufferAnswer)); //Corresponding functions to get the devices information. Depends on the application.
                    }
                    catch { break; }
                } while (bcSocket.ReceiveTimeout != 0); //fixed receive timeout for each adapter that supports our broadcast
                bcSocket.Close();
            }
        }
      }
      catch { }
  }
  return;
}

有关工作示例，请参阅 project：https：//github.com/xmegz/MndpTray

服务器定期发送广播消息。客户端接收并处理它们。许多主机信息（操作系统版本、IP 地址、网络接口等）发送 trought。UDP 广播 CDP LLDP