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我的一个程序有点问题。这是它应该如何工作的：

  1. C#客户端向Java服务器发送数据
  2. Java 服务器检查数据
  3. Java 服务器向 C# 客户端发回命令
  4. C#客户端接收数据并使用户能够登录或注册

我设法到达第 3 步，但现在我卡在第 4 步。

我在服务器、客户端和服务器上运行了 Wireshark。所有包裹都正确进出。服务器接收一个数据包并发出一个数据包。客户发出一份，收到一份。但是，如果我在控制台中检查 netstat，我看不到打开的端口。实际上我根本没有看到任何 UDP 套接字。所以数据包进来了，但 C# 客户端似乎没有听，为什么？

这是 C# 客户端。

// Opening a socket with UDP as Protocol type
Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
// The address of the server
IPAddress[] address = Dns.GetHostAddresses("192.168.0.87");
// The Endpoint with the port
IPEndPoint endPoint = new IPEndPoint(address[0], 40001);

// Defining the values I want
string values = "Something I send here";
// Encoding to byte with UTF8
byte[] data = Encoding.UTF8.GetBytes(values);

// Sending the values to the server on port 40001
socket.SendTo(data, endPoint);

// Showing what we sent
Console.WriteLine("Sent: " + values);

// Timeout for later, for now I just let the program get stuck
// socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 5000);

// Allowing the response to come in from everywhere
EndPoint response = new IPEndPoint(IPAddress.Any, 0);
// Buffer for server response (currently bigger then actually necessary for debugging)
byte[] responseData = new byte[1024];

//Receiving the data from the server
socket.ReceiveFrom(responseData, ref response);

// Outputing what we got, we don't even get here
Console.WriteLine("You got: " + Encoding.UTF8.GetString(responseData));

// Closing the socket
socket.Close();

For debugging, if the user authenticated successfully I want to send the string "Test" back.

Here is the Java server

// Printing to the server that the user username logged in successfully
System.out.println("User " + username + " logged in succesfully!");

// The byte buffer for the response, for now just Test
byte[] responseData = "Test".getBytes("UTF-8");
// The Datagram Packet, getting IP from the received packet and port 40001
DatagramPacket responsePacket = new DatagramPacket(responseData, responseData.length, receivePacket.getAddress(), 40001);
// Sending the response, tried putting Thread.sleep here didn't help
serverSocket.send(responsePacket);

I expect that I did something wrong with the C# client at the receive part but not sure what, any ideas or suggestions?

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2 回答 2

2

Maybe not the problem, but typically UDP responses are sent back to the originating (source) port of the original request. You are sending the response back to a fixed port. Can you try changing the Java bit to:

DatagramPacket responsePacket = new DatagramPacket(responseData, 
     responseData.length, receivePacket.getAddress(), receivePacket.getPort());
于 2012-05-04T07:38:13.830 回答
1

I believe you are missing the call to Bind on the client socket.

// Allowing the response to come in ON port 40001
EndPoint response = new IPEndPoint(IPAddress.Any, 40001);

socket.Bind(response);  // bind to port 40001 on some local address
于 2012-05-04T14:40:00.613 回答