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POOne-to-many TCP communications
 

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    <p>I am trying to put together a basic Java proof-of-concept to have a server (which will most likely just be a Windows or Linux laptop) that can send messages to a number of WIFI-connected android devices on the same subnet (initially 20-30, but it could be quite a number in the future - 2 or 300? - not sure, but I need to allow for the possibility). The app will send a message to all devices (the same message initially - but I may allow for special cases somewhere down the track). Each device can then reply, and I will want to check which ones replied and store the replies.</p> <p>I tried some test code using UDP (with some help from a tutorial on nakov.com), but it was very unreliable and the phone often locked up while trying to receive a packet - although it worked perfectly sometimes. My client code for the android device is shown below for reference (note, this code just sends a request for a message, and then receives and displays it - I hadn't got around to writing it the way I wanted it since it didn't seem reliable enough to use anyway).</p> <p>So, I think I probably need to use TCP for reliability (although I am open to suggestions). Would 2-300 individual TCP concurrent connections be ok? And its likely that all the replies would come in to the server at once (or over a 10-15 second period), would this flood it in a way it couldn't handle? Is it likely to be ok for only 20-30 devices?</p> <p>I know this is a kind of out-there question, but I'm hoping someone with more understanding of TCP than I have can shed some light and give me some pointers.</p> <p>Cheers</p> <p><strong>Steve</strong></p> <p>UDP Client App:</p> <pre><code>package nz.co.et.quoteclient; import java.io.IOException; import java.net.DatagramSocket; import java.net.DatagramPacket; import java.net.InetAddress; import java.net.SocketException; import java.net.UnknownHostException; import android.app.Activity; import android.content.Context; import android.net.wifi.WifiManager; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.TextView; import android.widget.Toast; public class QuoteClient extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button button = (Button) findViewById(R.id.Button01); button.setOnClickListener(new OnClickListener() { public void onClick(View v) { WifiManager wifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE); if (wifiManager.isWifiEnabled()) { TextView errorText = (TextView) findViewById(R.id.TextView01); int serverPort = 4445; InetAddress address = null; try { address = InetAddress.getByName("192.168.1.4"); } catch (UnknownHostException e) { errorText.setText("Failed at setting server IP Address"); e.printStackTrace(); } byte[] buf = new byte[256]; DatagramPacket packet = new DatagramPacket(buf, buf.length, address, serverPort); DatagramSocket socket = null; try { socket = new DatagramSocket(); } catch (SocketException e) { errorText.setText("Failed at creating socket"); e.printStackTrace(); } try { socket.send(packet); } catch (IOException e) { errorText.setText("Failed at sending request packet"); e.printStackTrace(); } // get response packet = new DatagramPacket(buf, buf.length); try { socket.receive(packet); } catch (IOException e) { errorText.setText("Failed at receiving quote packet from server"); e.printStackTrace(); } // display response String message = new String(packet.getData()); String data = ""; for (int i = 0; i &lt; message.length(); i++) { int tmp = (int) message.charAt(i); data = (tmp &lt;= 0 || tmp &gt;= 256) ? data += "" : data + message.charAt(i); } Toast.makeText(getApplicationContext(), data, Toast.LENGTH_LONG).show(); // errorText.setText(data); } else { Toast.makeText(getApplicationContext(), "WIFI not enabled", Toast.LENGTH_LONG).show(); } } }); } } </code></pre>
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    1. COWhen you say UDP do you mean UDP multicast?
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    2. CONo, I considered multicasting, but I was told it required supported hardware to work, and I just want someone holding a meeting to be able to fire this up on their laptop and either use the local wireless lan or at a stretch create an ad-hoc wireless lan for the event. Correct me if I am wrong about multicasting tho, cheers, Steve.
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