Java DatagramSocket发送但不接收

Question

I'm working on a game in Java, and I'm trying to communicate between a client and server on the same computer over the internet, and eventually between multiple computers. I used to be able to, but now the server doesn't seem to be receiving any packets from the client. I'll try to post all the relevant code.

This is on the server:

private DatagramSocket m_Socket = new DatagramSocket( 8000 );
private DatagramPacket m_DatagramPacket = new DatagramPacket( new byte[ 1024 ], 1024 );

...

while( true )
{
    m_Socket.receive( m_DatagramPacket );
    byte[] data = new byte[ 1024 ];
    data = m_DatagramPacket.getData( );
    System.out.println( "SERVER RECEIVING: " + data );
}

This is on the client:

private DatagramSocket m_Socket = new DatagramSocket( null );
private DatagramPacket m_DatagramPacket = new DatagramPacket( new byte[ 1024 ], 1024 );

...

m_DatagramPacket.setAddress( InetAddress.getByName( "72.49.50.49" ) );
m_DatagramPacket.setPort( 8000 );
m_DatagramPacket.setLength( length );
m_DatagramPacket.setData( data );

// "data" is the byte array, "length" is the length of the array

m_Socket.send( m_DatagramPacket );

I'm seeing the packet in Wireshark so I know it's sending.

EDIT: I may not understand how Wireshark works, is the screenshot below sending or receiving the packet?

Wireshark:

Firewall exception:

Port forwarding:

EDIT: I also ran this port tester program to test port 8000 and it says the port is open

UPDATE: For some reason I guess our routers were just refusing connections from the source local IP to the external IP destination. I can connect to the server using the local IP from the same network and using the external IP from a different network

Answer 1

If your client side you are creating an unbounded DatagramSocket (By passing null to the DatagramSocket(SocketAddress bindaddr) ) which means there will not be any originating port for that socket. Eventhough this might work, this is clearly not the correct approach. In your client side you must do the following change.

private DatagramSocket m_Socket = new DatagramSocket();
private DatagramPacket m_DatagramPacket = new DatagramPacket( new byte[ 1024 ], 1024 );

Using the Default DatagramSocket constructor will bind the socket to next available port and will guarantee that there is a source port involved in the communication.

And your firewall exception doesn't have a Source IP and Source Port pattern or restriction. Please check based on your Router whether this is required.

Answer 2

Firstly, assuming that your IP and other codes you write but not in above is correct,I have done a lot of test, even tried to change the settings of the firewall.But it still works. So, I think that maybe because of the unreliability of UDP protocol, your server sometimes can not receive the data from the client.You can just try to use TCP protocol.

Secondly, in your screenshot of PcWinTech.com v3.0.0 , it seems that your computer is in the subnetwork. So I gust that maybe the IP("72.49.50.49") is your router's IP, and I suggest you to check the settings of the router whether the router can transmit the data to your computer ,say, port forwarding.And I have just find a article that may help you.