Question

我的一个程序出了点问题。以下是它应该如何工作：

C＃Client将数据发送到Java服务器
Java服务器检查数据
Java服务器将命令发送回C＃客户端
C＃Client接收数据并允许用户登录或注册

我设法直到第3步，但现在我陷入第4步。

我在服务器和客户端以及服务器上运行了Wireshark。所有包都正确进出。服务器接收一个数据包并给出一个数据包。客户给出一个并收到一个。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();

对于调试，如果用户成功通过身份验证我想要发回字符串“Test”。

这是Java服务器

// 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);

我希望我在接收部分对C＃客户端做错了但不确定是什么，有什么想法或建议吗？

Answer 1

可能不是问题，但通常将UDP响应发送回原始请求的原始（源）端口。您将响应发送回固定端口。您可以尝试将Java位更改为：

DatagramPacket responsePacket = new DatagramPacket(responseData, 
     responseData.length, receivePacket.getAddress(), receivePacket.getPort());

Answer 2

我相信你在客户端套接字上错过了对Bind的调用。

// 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

C＃UDP Socket没有收听回复？

2 个答案: