guide to a simple unicast android udp server with c# udp client

Question

I want to create a very simple android UDP Uni cast server and a C# UDP client.Can we create server on android? if yes then what IP address should be given to c# client to be connected with android server?

Edit : I had completed the Uni-cast UDP server on my Android and uni-cast UDP client in C#. Server is sending DatagramPackets and client is receiving successfully. But the opposite is not happening, and there isn't any errors and exceptions. But I can't understand what's the problem in the code.

Android Server :

public class MainActivity extends Activity {

String myIP;
final Integer myPort = 12345;

String clientIP = "192.168.1.3"; 
Integer clientPort = 54321;

byte[] inBuffer,outBuffer;

Button send, set;
EditText sendMsg, receiveMsg, cip, cp;

DatagramSocket me;

AsyncTask<Void, byte[], Void> asyncReceiver;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    send = (Button) findViewById(R.id.button1);
    sendMsg = (EditText) findViewById(R.id.editText1);
    receiveMsg = (EditText) findViewById(R.id.editText2);

    set = (Button) findViewById(R.id.button2);
    cip = (EditText) findViewById(R.id.editText3);
    cp = (EditText) findViewById(R.id.editText4);

    inBuffer = new byte[256];
    outBuffer = new byte[256];

    myIP = null;
    myIP = GetCurrentIP();

    if (myIP == null) {
        Msg("GetCurrentIP error.");
    } else {
        try {
            setTitle(myIP+"|"+InetAddress.getLocalHost());
        } catch (UnknownHostException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
        if (!Bind()) {
            Msg("Bind() error.");
        } else {

            set.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    clientIP = cip.getText().toString();
                    clientPort = Integer.parseInt(cp.getText().toString());
                    Msg(clientIP+"|"+clientPort);
                }
            });

            send.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    outBuffer = sendMsg.getText().toString().getBytes();
                    SendToClient();
                }
            });

            //-----------
            asyncReceiver = new AsyncTask<Void, byte[], Void>() {

                @Override
                protected void onProgressUpdate(byte[]... values) {
                    // TODO Auto-generated method stub
                    super.onProgressUpdate(values);
                    receiveMsg.append(new String(values[0]));
                }

                @Override
                protected Void doInBackground(Void... params) {
                    // TODO Auto-generated method stub
                    try {
                        while(true){
                            inBuffer = new byte[256];
                            DatagramPacket pack = new DatagramPacket(inBuffer, inBuffer.length, InetAddress.getByName(clientIP), clientPort);
                            me.receive(pack);
                            publishProgress(inBuffer);
                            Thread.sleep(500);
                        }
                    } catch (Exception e) {
                        // TODO: handle exception
                        Msg(e.getMessage());
                    }
                    return null;
                }
            };
            //-----------
            asyncReceiver.execute(new Void[1]);
            Msg("Receiving started.");

        }
    }
}



private void SendToClient(){
    try {
        DatagramPacket pack = new DatagramPacket(outBuffer, outBuffer.length, InetAddress.getByName(clientIP), clientPort);
        me.send(pack);
        Msg("Sent successfully.");
    } catch (Exception e) {
        // TODO: handle exception
        Msg(e.getMessage());
    }
}

private boolean Bind(){
    try {
//          DatagramChannel channel = DatagramChannel.open();
//          me = channel.socket();
//          //me = new DatagramSocket();
//          SocketAddress localAddr = new InetSocketAddress(InetAddress.getByName(myIP), myPort);
//          me.bind(localAddr);
            me = new DatagramSocket(myPort, InetAddress.getByName(myIP));
            Msg("Bound Successfully.");
            return true;
        } catch (SocketException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            Msg(e.getMessage());
        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            Msg(e.getMessage());
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return false;
    }

private String GetCurrentIP(){
    WifiManager wifiMgr = (WifiManager) getSystemService(WIFI_SERVICE);
    return Formatter.formatIpAddress(wifiMgr.getConnectionInfo().getIpAddress());
}

public void Msg(String msg){
    Toast.makeText(getApplicationContext(), msg, Toast.LENGTH_SHORT).show();
    Log.v(">>>>>", msg);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}
}

c# client...

public partial class Form1 : Form
 {
      Socket me;
      EndPoint myEndPoint;

      byte[] inBuffer, outBuffer;

      EndPoint serverEP;

      private void SendToClient()
      {
           if (serverEP == null)
           {
                serverEP = new IPEndPoint(IPAddress.Parse(textBoxsip.Text), int.Parse(textBoxsp.Text));
           }
           try
           {
                lock (me)
                {
                     outBuffer = new byte[256];
                     outBuffer = Encoding.Default.GetBytes(textBoxmsg.Text);
                     me.SendTo(outBuffer, serverEP);
                }
                Task.Run(() => MessageBox.Show("Sent"));
           }
           catch (Exception ex)
           {
                MessageBox.Show(ex.Message);
           }
      }

      private String GetCurrentIP()
      {
          IPAddress[] ips = Dns.GetHostAddresses(Dns.GetHostName());
          var selectedIPs = from ip in ips
                            where ip.AddressFamily == AddressFamily.InterNetwork
                            select ip;
          return selectedIPs.First().ToString();
      }

      public Form1()
      {
           InitializeComponent();

           inBuffer = new byte[256];
           outBuffer = new byte[256];
      }

      private void Form1_Load(object sender, EventArgs e)
      {
           this.Text = GetCurrentIP();

           me = new Socket
           (
                AddressFamily.InterNetwork,
                SocketType.Dgram,
                ProtocolType.Udp
           );
      }

      private void buttonBind_Click(object sender, EventArgs e)
      {
           try
           {
                myEndPoint = new IPEndPoint(IPAddress.Parse(textBoxBip.Text), int.Parse(textBoxBp.Text));
                me.Bind(myEndPoint);
                Task.Run(()=> MessageBox.Show("Bound Successfully."));
           }
           catch (Exception ex)
           {
                MessageBox.Show(ex.Message);
           }
      }

      private void buttonReceiveFrom_Click(object sender, EventArgs e)
      {
           if (serverEP == null)
           {
                serverEP = new IPEndPoint(IPAddress.Parse(textBoxsip.Text), int.Parse(textBoxsp.Text));
           }
           try
           {
                me.BeginReceiveFrom
                (
                     inBuffer,
                     0,
                     inBuffer.Length,
                     SocketFlags.None,
                     ref serverEP,
                     new AsyncCallback(onReceiveComplete),
                     null
                );
           }
           catch (Exception ex)
           {
                MessageBox.Show(ex.Message);
           }
      }

      private void onReceiveComplete(IAsyncResult ar)
      {
           try
           {
                int nobs = me.EndReceiveFrom(ar, ref serverEP);

                if (nobs > 0)
                {
                     AddtoListBox(Encoding.Default.GetString(inBuffer));
                }

                inBuffer = new byte[256];

                me.BeginReceiveFrom
                (
                     inBuffer,
                     0,
                     inBuffer.Length,
                     SocketFlags.None,
                     ref serverEP,
                     new AsyncCallback(onReceiveComplete),
                     null
                );
           }
           catch (Exception ex)
           {
                MessageBox.Show(ex.Message);
           }
      }

      private void AddtoListBox(String msg)
      {
           this.Invoke((Action)delegate(){listBox1.Items.Add(msg);});
      }

      private void buttonSendTo_Click(object sender, EventArgs e)
      {
           SendToClient();
      }
 }
}

Answer 1

Here is a good c# <--> android udp example: Android client finding C# server automatically

C#

//receive UDP packet
                int port = (int)float.Parse(Variables.port_key);
                UdpCient UDP_packet = new UdpClient(port);
                UDP_packet.EnableBroadcast = true;
                IPEndPoint RemoteIpEndPoint = new IPEndPoint(IPAddress.Any, 0);
                IPAddress from_addr = null;
                Boolean gogo = false;
                while (!gogo)
                {
                    Byte[] receiveBytes = UDP_packet.Receive(ref RemoteIpEndPoint);
                    string returnData = Encoding.UTF8.GetString(receiveBytes);
                    if (returnData.ToString() == "83hcX1")
                    {
                        gogo = true;
                    }
                    from_addr = RemoteIpEndPoint.Address;
                }
                //send UDP packet
                IPEndPoint ipEndPoint = new IPEndPoint(from_addr, port);
                Byte[] sendBytes = Encoding.UTF8.GetBytes("94dbF5");
                UDP_packet.Send(sendBytes, sendBytes.Length, ipEndPoint);
                UDP_packet.Close();

Android

                    //send UDP packet
                    DatagramSocket UDP_packet = new DatagramSocket(SERVERPORT);
                    UDP_packet.setBroadcast(true);
                    byte[] b = "83hcX1".getBytes("UTF-8");
                    DatagramPacket outgoing = new DatagramPacket(b, b.length, getBroadcastAddress(Main.this), SERVERPORT);                  
                    UDP_packet.send(outgoing);
                    //receive UDP packet
                    boolean gogo = false;
                    while (!gogo) {                     
                        byte[] buffer = new byte[1024];
                        DatagramPacket incoming = new DatagramPacket(buffer, buffer.length);    
                        UDP_packet.receive(incoming);
                        String message = new String(incoming.getData(), 0, incoming.getLength(), "UTF-8");
                         if (message.equals("94dbF5")) {
                             gogo = true;
                             SERVER_IP = incoming.getAddress();
                         }                  
                    }               
                    UDP_packet.close();

InetAddress getBroadcastAddress(Context context) throws IOException {
    WifiManager wifi = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
    DhcpInfo dhcp = wifi.getDhcpInfo();
    if (dhcp == null) {
          return null;
        }
    int broadcast = (dhcp.ipAddress & dhcp.netmask) | ~dhcp.netmask;
    byte[] quads = new byte[4];
    for (int k = 0; k < 4; k++)
      quads[k] = (byte) ((broadcast >> k * 8) & 0xFF);
    return InetAddress.getByAddress(quads);
}

Some routers (maybe 5%) block UDP broadcast, so... be careful.

Get Android (server) IP:

InetAddress getBroadcastAddress(Context context) throws IOException {
        WifiManager wifi = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
        DhcpInfo dhcp = wifi.getDhcpInfo();
        if (dhcp == null) {
              return null;
            }
        int broadcast = (dhcp.ipAddress & dhcp.netmask) | ~dhcp.netmask;
        byte[] quads = new byte[4];
        for (int k = 0; k < 4; k++)
          quads[k] = (byte) ((broadcast >> k * 8) & 0xFF);
        return InetAddress.getByAddress(quads);
    }