How To Make JmDNS Work On A Large Network

Question

I'm working on adding discovery to our app using (http://jmdns.sourceforge.net/). It's actually working correctly on my small home network. But it fails on the large network at the office. I seem to recall reading that if an app blocks for more than 5 seconds that it get's reset. And that appears to be what's happening. But first, how can I be sure that's actually the problem?

Of course, my main question is how can I can make JmDNS work on a large network. And the more general question is what do you do when you need more than 5 seconds?

Small snippet of my code (it's in an AsyncTask):

InetAddress bindingAddress = InetAddress.getByName(ipOfThisDevice);

jmdns = JmDNS.create(bindingAddress);

serviceList = Arrays.asList(jmdns.list("_myappname._tcp.local.",5000)); // 5 second timeout

Answer 1

Have a look at http://developer.android.com/training/connect-devices-wirelessly/nsd.html - that should get you started if you are running on Android

Answer 2

Here is the code I used in my Android app which you say seems to work at your office?

 /*
    ZeroConf Browser - http://melloware.com/

    Copyright (C) 2010 Melloware Inc
    All Rights Reserved.
 */
package com.melloware.zeroconf;

import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.TreeMap;

import javax.jmdns.JmDNS;
import javax.jmdns.ServiceEvent;
import javax.jmdns.ServiceInfo;
import javax.jmdns.ServiceListener;
import javax.jmdns.ServiceTypeListener;

import android.app.ExpandableListActivity;
import android.content.Context;
import android.net.wifi.WifiInfo;
import android.net.wifi.WifiManager;
import android.net.wifi.WifiManager.MulticastLock;
import android.os.Bundle;
import android.text.Html;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.ImageView;
import android.widget.TextView;

/**
 * Service tab which contains the expandable list of DNS Services and the details of each service type as they are
 * gathered.
 * <p>
 * Copyright (c) 2010 Melloware, Inc. <http://www.melloware.com>
 * @author Emil A. Lefkof III <[e-mail]>
 * @version 1.0
 */
public class ServiceActivity extends ExpandableListActivity implements ServiceListener, ServiceTypeListener {

   /**
    * Tag used for logging
    */
   private static final String TAG = ServiceActivity.class.getName();

   /**
    * Value used to identify in ZeroConf
    */
   private static final String HOSTNAME = "melloware";

   /**
    * Sorted array of top level items which are the Service Types
    */
   public static final ArrayList<ServiceType> GROUPS = new ArrayList<ServiceType>();

   /**
    * Sorted list of the details for each service type
    */
   public static final TreeMap<String, ArrayList<ServiceInfo>> DETAILS = new TreeMap<String, ArrayList<ServiceInfo>>();

   /**
    * Instance of Bonjour/Rendezvous/ZeroConf handler
    */
   public static JmDNS jmdns = null;

   /**
    * Allows an application to receive Wifi Multicast packets.
    */
   private static MulticastLock multicastLock = null;

   /**
    * The backing adapter for the ListView of services
    */
   private static DNSExpandableListAdapter mAdapter;

   @Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      mAdapter = new DNSExpandableListAdapter();
      setListAdapter(mAdapter);
   }

   /*
    * (non-Javadoc)
    * @see android.app.Activity#onStart()
    */
   @Override
   protected void onStart() {
      Log.i(TAG, "Starting ServiceActivity...");
      super.onStart();
      try {
         Log.i(TAG, "Starting Mutlicast Lock...");
         WifiManager wifi = (WifiManager) this.getSystemService(Context.WIFI_SERVICE);
         // get the device ip address
         final InetAddress deviceIpAddress = getDeviceIpAddress(wifi);
         multicastLock = wifi.createMulticastLock(getClass().getName());
         multicastLock.setReferenceCounted(true);
         multicastLock.acquire();
         Log.i(TAG, "Starting ZeroConf probe....");
         jmdns = JmDNS.create(deviceIpAddress, HOSTNAME);
         jmdns.addServiceTypeListener(this);
      } catch (IOException ex) {
         Log.e(TAG, ex.getMessage(), ex);
      }
      Log.i(TAG, "Started ZeroConf probe....");
   }

   /*
    * (non-Javadoc)
    * @see android.app.ActivityGroup#onStop()
    */
   @Override
   protected void onStop() {
      Log.i(TAG, "Stopping ServiceActivity...");
      super.onStop();
      stopScan();
      DETAILS.clear();
      GROUPS.clear();
      if (!isFinishing()) {
         mAdapter.notifyDataSetChanged();
      }
   }

   /**
    * Stops scanning and cleans up locks.
    */
   private static void stopScan() {
      try {
         if (jmdns != null) {
            Log.i(TAG, "Stopping ZeroConf probe....");
            jmdns.unregisterAllServices();
            jmdns.close();
            jmdns = null;
         }
         if (multicastLock != null) {
            Log.i(TAG, "Releasing Mutlicast Lock...");
            multicastLock.release();
            multicastLock = null;
         }
      } catch (Exception ex) {
         Log.e(TAG, ex.getMessage(), ex);
      }
   }

   /**
    * Gets the current Android device IP address or return 10.0.0.2 which is localhost on Android.
    * <p>
    * @return the InetAddress of this Android device
    */
   private InetAddress getDeviceIpAddress(WifiManager wifi) {
      InetAddress result = null;
      try {
         // default to Android localhost
         result = InetAddress.getByName("10.0.0.2");

         // figure out our wifi address, otherwise bail
         WifiInfo wifiinfo = wifi.getConnectionInfo();
         int intaddr = wifiinfo.getIpAddress();
         byte[] byteaddr = new byte[] { (byte) (intaddr & 0xff), (byte) (intaddr >> 8 & 0xff), (byte) (intaddr >> 16 & 0xff), (byte) (intaddr >> 24 & 0xff) };
         result = InetAddress.getByAddress(byteaddr);
      } catch (UnknownHostException ex) {
         Log.w(TAG, String.format("getDeviceIpAddress Error: %s", ex.getMessage()));
      }

      return result;
   }

   /**
    * Delegate method from mDNS when a service is added.
    */
   public void serviceAdded(ServiceEvent event) {
      Log.i(TAG, String.format("ZeroConf serviceAdded(event=\n%s\n)", event.toString()));
      ArrayList<ServiceInfo> list = DETAILS.get(event.getType());
      if (list != null) {
         ServiceInfo info = event.getInfo();
         if (!list.contains(info)) {
            list.add(info);
         }
      }
   }

   /**
    * Delegate method from mDNS when a service is removed.
    */
   public void serviceRemoved(ServiceEvent event) {
      Log.w(TAG, String.format("ZeroConf serviceRemoved(event=\n%s\n)", event.toString()));

   }

   /**
    * Delegate method from mDNS when a service is resolved.
    */
   public void serviceResolved(ServiceEvent event) {
      Log.i(TAG, String.format("ZeroConf serviceResolved(event=\n%s\n)", event.toString()));
      ArrayList<ServiceInfo> list = DETAILS.get(event.getType());
      if (list != null) {
         ServiceInfo info = event.getInfo();
         if (!list.contains(info)) {
            list.add(info);
         }
      }
   }

   /**
    * Delegate method from mDNS when a new service type is discovered.
    */
   public void serviceTypeAdded(final ServiceEvent event) {
      Log.i(TAG, String.format("ZeroConf serviceTypeAdded(event=\n%s\n)", event.toString()));
      jmdns.addServiceListener(event.getType(), this);
      runOnUiThread(new Runnable() {
         public void run() {
            final ServiceType type = new ServiceType();
            type.setName(event.getType());
            GROUPS.add(type);
            Collections.sort(GROUPS);
            DETAILS.put(event.getType(), new ArrayList<ServiceInfo>());
            mAdapter.notifyDataSetChanged();
         }
      });
   }

   /**
    * Delegate method from mDNS when a subtype is discovered.
    */
   public void subTypeForServiceTypeAdded(ServiceEvent event) {
      Log.i(TAG, String.format("ZeroConf subTypeForServiceTypeAdded(event=\n%s\n)", event.toString()));
   }

   /**
    * When a scan is complete show a message if no services found.
    * <p>
    * @param context the ApplicationContext
    */
   public static void scanFinished(Context context) {
      if (GROUPS.size() == 0) {
         final ServiceType type = new ServiceType();
         type.setName(context.getResources().getString(R.string.msg_noservices));
         GROUPS.add(type);
         mAdapter.notifyDataSetChanged();
         stopScan();
      }
   }

   /**
    * ExpandableListAdapter that displays the Service Types as groups and when each Service Type is expanded displays a
    * list of all discovered Services for that Service Type.
    */
   public class DNSExpandableListAdapter extends BaseExpandableListAdapter {

      LayoutInflater inflater = LayoutInflater.from(getApplicationContext());

      public Object getChild(int groupPosition, int childPosition) {
         try {
            Iterator<ArrayList<ServiceInfo>> it = DETAILS.values().iterator();
            int i = 0;
            while (it.hasNext()) {
               ArrayList<ServiceInfo> type = it.next();
               if (i == groupPosition) {
                  ServiceInfo service = type.get(childPosition);
                  ServiceInfo resolvedService = jmdns.getServiceInfo(service.getType(), service.getName());
                  if (resolvedService != null) {
                     service = resolvedService;
                  }
                  StringBuffer buf = new StringBuffer();
                  buf.append("<b>");
                  buf.append(service.getName());
                  buf.append("</b><br/>");
                  buf.append(service.getTypeWithSubtype());
                  buf.append("<br/>");
                  buf.append(service.getServer());
                  buf.append(':');
                  buf.append(service.getPort());
                  buf.append("<br/>");
                  buf.append(service.getInetAddresses()[0]);
                  buf.append("<br/>");
                  for (Enumeration<String> names = service.getPropertyNames(); names.hasMoreElements();) {
                     buf.append("<br/>");
                     String prop = names.nextElement();
                     buf.append("<b>");
                     buf.append(prop);
                     buf.append("</b>");
                     buf.append(" = ");
                     buf.append("<i>");
                     buf.append(service.getPropertyString(prop));
                     buf.append("</i>");
                  }
                  return buf.toString();
               }
               i++;
            }
         } catch (Exception e) {
            Log.w("Exception", e);
         }

         return "Not Available";
      }

      public long getChildId(int groupPosition, int childPosition) {
         return childPosition;
      }

      public int getChildrenCount(int groupPosition) {
         Iterator<ArrayList<ServiceInfo>> it = DETAILS.values().iterator();
         int i = 0;
         while (it.hasNext()) {
            ArrayList<ServiceInfo> type = it.next();
            if (i == groupPosition) {
               return type.size();
            }
            i++;
         }
         return 1;
      }

      public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
         convertView = this.inflater.inflate(R.layout.child_row, parent, false);
         ((TextView) convertView.findViewById(R.id.childvalue)).setText(Html.fromHtml(getChild(groupPosition, childPosition).toString()));
         return convertView;
      }

      public Object getGroup(int groupPosition) {
         return GROUPS.get(groupPosition);
      }

      public int getGroupCount() {
         return GROUPS.size();
      }

      public long getGroupId(int groupPosition) {
         return groupPosition;
      }

      public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
         convertView = this.inflater.inflate(R.layout.group_row, parent, false);
         ServiceType type = (ServiceType) getGroup(groupPosition);
         ImageView imageView = (ImageView) convertView.findViewById(R.id.serviceicon);
         imageView.setImageResource(type.getImageIcon());
         ((TextView) convertView.findViewById(R.id.service)).setText(type.toString());
         return convertView;
      }

      public boolean isChildSelectable(int groupPosition, int childPosition) {
         return true;
      }

      public boolean hasStableIds() {
         return true;
      }
   }

}