Question

我有一个异步UDP服务器类，其中一个套接字绑定在IPAddress.Any上，我想知道收到的数据包被发送到哪个IP地址（...或接收到）。似乎我不能只使用Socket.LocalEndPoint属性，因为它总是返回0.0.0.0（这是有意义的，因为它绑定到...）。

以下是我目前正在使用的代码的有趣部分：

private Socket udpSock;
private byte[] buffer;
public void Starter(){
    //Setup the socket and message buffer
    udpSock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
    udpSock.Bind(new IPEndPoint(IPAddress.Any, 12345));
    buffer = new byte[1024];

    //Start listening for a new message.
    EndPoint newClientEP = new IPEndPoint(IPAddress.Any, 0);
    udpSock.BeginReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref newClientEP, DoReceiveFrom, udpSock);
}

private void DoReceiveFrom(IAsyncResult iar){
    //Get the received message.
    Socket recvSock = (Socket)iar.AsyncState;
    EndPoint clientEP = new IPEndPoint(IPAddress.Any, 0);
    int msgLen = recvSock.EndReceiveFrom(iar, ref clientEP);
    byte[] localMsg = new byte[msgLen];
    Array.Copy(buffer, localMsg, msgLen);

    //Start listening for a new message.
    EndPoint newClientEP = new IPEndPoint(IPAddress.Any, 0);
    udpSock.BeginReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref newClientEP, DoReceiveFrom, udpSock);

    //Handle the received message
    Console.WriteLine("Recieved {0} bytes from {1}:{2} to {3}:{4}",
                      msgLen,
                      ((IPEndPoint)clientEP).Address,
                      ((IPEndPoint)clientEP).Port,
                      ((IPEndPoint)recvSock.LocalEndPoint).Address,
                      ((IPEndPoint)recvSock.LocalEndPoint).Port);
    //Do other, more interesting, things with the received message.
}

如前所述，这总是打印一行如下：

从127.0.0.1:1678收到32个字节到0.0.0.0:12345

我希望它类似于：

从127.0.0.1:1678收到32个字节到127.0.0.1:12345

提前感谢您对此的任何想法！ --Adam

更新

好吧，我找到了一个解决方案，虽然我不喜欢它...基本上，我没有打开绑定到IPAddress.Any的单个udp套接字，而是为每个可用的IPAddress创建一个唯一的套接字。因此，新的Starter功能如下所示：

public void Starter(){
    buffer = new byte[1024];

    //create a new socket and start listening on the loopback address.
    Socket lSock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
    lSock.Bind(new IPEndPoint(IPAddress.Parse("127.0.0.1"), 12345);

    EndPoint ncEP = new IPEndPoint(IPAddress.Any, 0);
    lSock.BeginReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref ncEP, DoReceiveFrom, lSock);

    //create a new socket and start listening on each IPAddress in the Dns host.
    foreach(IPAddress addr in Dns.GetHostEntry(Dns.GetHostName()).AddressList){
        if(addr.AddressFamily != AddressFamily.InterNetwork) continue; //Skip all but IPv4 addresses.

        Socket s = new Socket(addr.AddressFamily, SocketType.Dgram, ProtocolType.Udp);
        s.Bind(new IPEndPoint(addr, 12345));

        EndPoint newClientEP = new IPEndPoint(IPAddress.Any, 0);
        s.BeginReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref newClientEP, DoReceiveFrom, s);
    }
}

这只是为了说明这个概念，这个代码最大的问题就是每个套接字试图使用相同的缓冲区......这通常是一个坏主意......

必须有一个更好的解决方案;我的意思是，源和目标是UDP数据包头的一部分！哦，好吧，我想我会继续这样做，直到有更好的东西。

Answer 1

我遇到了同样的问题。我没有看到使用ReceiveFrom或其异步变体检索收到的数据包的目标地址的方法。

但是......如果您使用ReceiveMessageFrom或其变体，则会获得IPPacketInformation（ReceiveMessageFrom和EndReceiveMessageFrom的参考，或作为SocketAsyncEventArgs传递给ReceiveMessageFromAsync中的回调。该对象将包含接收数据包的IP地址和接口号。

（注意，此代码尚未经过测试，因为我使用了ReceiveMessageFromAsync而不是伪造的假开始/结束调用。）

private void ReceiveCallback(IAsyncResult iar)
{
    IPPacketInformation packetInfo;
    EndPoint remoteEnd = new IPEndPoint(IPAddress.Any, 0);
    SocketFlags flags = SocketFlags.None;
    Socket sock = (Socket) iar.AsyncState;

    int received = sock.EndReceiveMessageFrom(iar, ref flags, ref remoteEnd, out packetInfo);
    Console.WriteLine(
        "{0} bytes received from {1} to {2}",
        received,
        remoteEnd,
        packetInfo.Address
    );
}

注意，您应该在 SetSocketOption(SocketOptionLevel.IP, SocketOptionName.PacketInformation, true) 之前将Bind作为设置套接字的一部分。 ... ReceiveMessageFrom ...方法将为您设置它，但您可能只会看到在设置选项后Windows看到的任何数据包的有效信息。（在实践中，这不是一个问题 - 但是如果/如果它曾经发生过，原因将是一个谜。最好完全防止它。）

Answer 2

我认为如果你绑定到127.0.0.1而不是IPAddress.Any你会得到你想要的行为。

0.0.0.0故意意味着“每个可用的IP地址”，并且它在字面上是由于您的绑定语句。

Answer 3

从该套接字获取地址的一种方法是将其连接到发件人。一旦你这样做，你将能够获得本地地址（或至少一个可路由到发送者），但是，你只能从连接的端点接收消息。

要取消连接，您需要再次使用连接，这次指定一个系列为AF_UNSPEC的地址。不幸的是，我不知道如何在C＃中实现这一目标。

（免责声明：我从来没有写过一行C＃，这一般适用于Winsock）

Answer 4

关于缓冲区问题，请尝试以下方法：

创建一个名为StateObject的类，用于存储您希望在回调中拥有的任何数据，并使用缓冲区，如果您需要，还包括套接字（因为我看到您当前正在将udpSock作为stateObject传递）。将新创建的对象传递给异步方法，然后您将在回调中访问它。

public void Starter(){
    StateObject state = new StateObject();
    //set any values in state you need here.

    //create a new socket and start listening on the loopback address.
    Socket lSock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
    lSock.Bind(new IPEndPoint(IPAddress.Parse("127.0.0.1"), 12345);

    EndPoint ncEP = new IPEndPoint(IPAddress.Any, 0);
    lSock.BeginReceiveFrom(state.buffer, 0, state.buffer.Length, SocketFlags.None, ref ncEP,    DoReceiveFrom, state);

    //create a new socket and start listening on each IPAddress in the Dns host.
    foreach(IPAddress addr in Dns.GetHostEntry(Dns.GetHostName()).AddressList){
        if(addr.AddressFamily != AddressFamily.InterNetwork) continue; //Skip all but IPv4 addresses.

        Socket s = new Socket(addr.AddressFamily, SocketType.Dgram, ProtocolType.Udp);
        s.Bind(new IPEndPoint(addr, 12345));

        EndPoint newClientEP = new IPEndPoint(IPAddress.Any, 0);

        StateObject objState = new StateObject();
        s.BeginReceiveFrom(objState.buffer, 0, objState.buffer.length, SocketFlags.None, ref newClientEP, DoReceiveFrom, objState);
     }
}

在搜索这个问题时，我发现：

http://msdn.microsoft.com/en-us/library/system.net.sockets.socket.beginreceivefrom.aspx

然后，您可以像正在使用udpSock和缓冲区一样从AsyncState转换StateObject，以及您需要的任何其他数据将存储在那里。

我想现在唯一的问题是如何以及在何处存储数据，但由于我不知道您的实现，我无法帮助那里。

Answer 5

亚当

这未经过测试......让我们试试

private void DoReceiveFrom(IAsyncResult iar){
//Get the received message.
Socket recvSock = (Socket)iar.AsyncState;
//EndPoint clientEP = new IPEndPoint(IPAddress.Any, 0);
Socket clientEP = recvSock.EndAccept(iar);
int msgLen = recvSock.EndReceiveFrom(iar, ref clientEP);
byte[] localMsg = new byte[msgLen];
Array.Copy(buffer, localMsg, msgLen);

//Start listening for a new message.
EndPoint newClientEP = new IPEndPoint(IPAddress.Any, 0);
udpSock.BeginReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref newClientEP, DoReceiveFrom, udpSock);

//Handle the received message
/*
Console.WriteLine("Recieved {0} bytes from {1}:{2} to {3}:{4}",
                  msgLen,
                  ((IPEndPoint)recvSock.RemoteEndPoint).Address,
                  ((IPEndPoint)recvSock.RemoteEndPoint).Port,
                  ((IPEndPoint)recvSock.LocalEndPoint).Address,
                  ((IPEndPoint)recvSock.LocalEndPoint).Port);
//Do other, more interesting, things with the received message.
*/
Console.WriteLine("Recieved {0} bytes from {1}:{2} to {3}",
                  msgLen,
                  ((IPEndPoint)recvSock.RemoteEndPoint).Address,
                  ((IPEndPoint)recvSock.RemoteEndPoint).Port,
                  clientEP.RemoteEP.ToString();
 }

C＃UDP套接字：获取接收者地址

5 个答案: