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Android App Connecting to Node.js server using Socket.io

Posted by: admin November 17, 2017 Leave a comment

Questions:

I’m having trouble getting my Android app to connect to a socket.io chat server. I’m using socket.io-java-client created by Gottox which can be found here: https://github.com/Gottox/socket.io-java-client

The server runs locally over port 7000. I’m using the android emulator, so I’m using 10.0.2.2:7000 to access the server.

Any help would be appreciated, I don’t have much experience at all with SSL. If I find a working solution I’ll also post it.

Node.js Server

var express = require('express');
var app = express();
var server = require('http').createServer(app).listen(7000);
var io = require('socket.io').listen(server);
io.sockets.on('connection', function(client){
    client.on('message', function(err, msg){
        client.broadcast.emit('message', msg);
    });
 });

package.json

{
  "name": "simplechat",
  "version": "0.0.1",
  "main": "app.js",
  "dependencies": {
    "express" : "~4.0.0",
    "socket.io" : "~0.9.13"
  }
}

Android: SendMessageActivity

public class SendMessageActivity extends Activity {

    private static final String SERVER_ADDRESS = "https://10.0.2.2:7000";

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

        System.out.println("Sever: " + SERVER_ADDRESS);

        try {
            SocketIO socket = new SocketIO(new URL(SERVER_ADDRESS), new IOCallback() {
                @Override
                public void onDisconnect() {
                    System.out.println("disconnected");
                }

                @Override
                public void onConnect() {
                    System.out.println("connected");
                }

                @Override
                public void onMessage(String s, IOAcknowledge ioAcknowledge) {
                }

                @Override
                public void onMessage(JSONObject jsonObject, IOAcknowledge ioAcknowledge) {
                }

                @Override
                public void on(String event, IOAcknowledge ioAcknowledge, Object... objects) {
                }

                @Override
                public void onError(SocketIOException e) {
                    e.printStackTrace();
                }
            });

        } catch (MalformedURLException ex) {
            ex.printStackTrace();
        }
    }

Android Permissions

<uses-permission
    android:name="android.permission.INTERNET">
</uses-permission>

Error Code

08-09 16:07:28.224    8411-8441/com.example.puma.chatexample W/System.err﹕ io.socket.SocketIOException: Error while handshaking
08-09 16:07:28.225    8411-8441/com.example.puma.chatexample W/System.err﹕ at io.socket.IOConnection.handshake(IOConnection.java:322)
08-09 16:07:28.225    8411-8441/com.example.puma.chatexample W/System.err﹕ at io.socket.IOConnection.access$600(IOConnection.java:39)
08-09 16:07:28.225    8411-8441/com.example.puma.chatexample W/System.err﹕ at io.socket.IOConnection$ConnectThread.run(IOConnection.java:199)
08-09 16:07:28.226    8411-8441/com.example.puma.chatexample W/System.err﹕ Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'javax.net.ssl.SSLSocketFactory javax.net.ssl.SSLContext.getSocketFactory()' on a null object reference
08-09 16:07:28.226    8411-8441/com.example.puma.chatexample W/System.err﹕ at io.socket.IOConnection.handshake(IOConnection.java:302)
08-09 16:07:28.227    8411-8441/com.example.puma.chatexample W/System.err﹕ ... 2 more
Answers:

I actually solved the problem. I used my PC’s local IP http://192.168.0.xxx:7000 and the app was able to connect to the chat server from the emulator. I don’t know why this works, but it might help out someone in the future 🙂

Update:

This is how I ended up structuring the project. I created a singleton class to handle socket connections Android side (you could also do it as a service). When receiving a message, the singleton class broadcasts an intent to the rest of the app. The intent is then picked up by a broadcast receiver in the relevant activity.

Android Side (singleton):

public class SocketSingleton {

    private static SocketSingleton instance;
    private static final String SERVER_ADDRESS = "http://1.2.3.4:1234";
    private SocketIO socket;
    private Context context;

    public static SocketSingleton get(Context context){
        if(instance == null){
            instance = getSync(context);
        }
        instance.context = context;
        return instance;
    }

    public static synchronized SocketSingleton getSync(Context context){
        if (instance == null) {
            instance = new SocketSingleton(context);
        }
        return instance;
    }

    public SocketIO getSocket(){
        return this.socket;
    }

    private SocketSingleton(Context context){
        this.context = context;
        this.socket = getChatServerSocket();
        this.friends = new ArrayList<Friend>();
    }

    private SocketIO getChatServerSocket(){
        try {
            SocketIO socket = new SocketIO(new URL(SERVER_ADDRESS), new IOCallback() {
                @Override
                public void onDisconnect() {
                    System.out.println("disconnected");
                }

                @Override
                public void onConnect() {
                    System.out.println("connected");
                }

                @Override
                public void on(String event, IOAcknowledge ioAcknowledge, Object... objects) {
                    if (event.equals("chatMessage")) {
                        JSONObject json = (JSONObject) objects[0];
                        ChatMessage chatMessage = new ChatMessage(json);

                        Intent intent = new Intent();
                        intent.setAction("newChatMessage");
                        intent.putExtra("chatMessage", chatMessage);
                        context.sendBroadcast(intent);
                    }
                }
                @Override
                public void onError(SocketIOException e) {
                    e.printStackTrace();
                }
            });
            return socket;
        } catch (MalformedURLException ex) {
            ex.printStackTrace();
        }
        return null;
    }
}

Android Side (activity):

public class ChatActivity extends Activity {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_chat);
    IntentFilter newChatMessageFilter = new IntentFilter("newChatMessage");
    this.registerReceiver(new MessageReceiver(), newChatMessageFilter);

    ...

    public class MessageReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent){
            final ChatMessage chatMessage =(ChatMessage) intent.getExtras().get("chatMessage");
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    mAdapter.add(chatMessage);
                    mAdapter.notifyDataSetChanged();
                }
            });
        }
    }
} 

Server Side:

var express = require('express');
var app = express();
var server = require('http').createServer(app).listen(1234);
var io = require('socket.io').listen(server);

io.sockets.on('connection', function(client){

    console.log("client connected: " + client.id);

    client.on("sendTo", function(chatMessage){
        console.log("Message From: " + chatMessage.fromName);
        console.log("Message To: " + chatMessage.toName);


        io.sockets.socket(chatMessage.toClientID).emit("chatMessage", {"fromName" : chatMessage.fromName,
                                                                    "toName" : chatMessage.toName,
                                                                    "toClientID" : chatMessage.toClientID,
                                                                    "msg" : chatMessage.msg});

    });
});

Questions:
Answers:

I know this not really answers to the OP’s posts, but for those who may be interested, this is a tutorial I made to make communicate your Android with a Node.js server –without any additional library– :

https://causeyourestuck.io/2016/04/27/node-js-android-tcpip/

This is a foretaste of how it looks like at the end:

Client socket = new Client("192.168.0.8", 1234);
socket.setOnEventOccurred(new Client.OnEventOccurred() {
    @Override
    public void onMessage(String message) {
    }

    @Override
    public void onConnected(Socket socket) {
        socket.send("Hello World!");
        socket.disconnect();
    }

    @Override
    public void onDisconnected(Socket socket, String message) {
    }
});

socket.connect();

Questions:
Answers:

You’re emulator network is different from your PC’s as I have heard. So if you could by change try this on an actual phone that is connected to the same network as your PC.

You probably wont be able to ping 10.0.2.2 from your emulator or the other way around from your pc to emulator.

Questions:
Answers:

Puma has already answered on how you can implement a socket connection using SocketIO. This has nothing new to contribute. Yet, it is an attempt to help fellow newbies, as also introduce the implementation of Socket.io’s java library.

Socket.IO has its own java implementation on Github, which you can follow along to create a socket application for Android/Java.

Android side:

Include this in your build gradle

compile ('io.socket:socket.io-client:0.8.3') {
    // excluding org.json which is provided by Android
    exclude group: 'org.json', module: 'json'
}

Provide Permission in your app:

<uses-permission android:name="android.permission.INTERNET" />

Android Code:
The structure of code is similar to how you would code in Node. The message in socket.on is similar to node’s socket.on(‘message’, …)

import io.socket.client.Socket;
import io.socket.client.IO;
import io.socket.emitter.Emitter;

final Socket socket;
try{
socket = IO.socket("http://192.168.1.1:8080");

socket.on(Socket.EVENT_CONNECT, new Emitter.Listener() {

    @Override
    public void call(Object... args) {
        socket.emit("message", "hi");
        socket.disconnect();
    }

}).on("message", new Emitter.Listener() {
        //message is the keyword for communication exchanges
    @Override
    public void call(Object... args) {
        socket.emit("message", "hi");
    }

}).on(Socket.EVENT_DISCONNECT, new Emitter.Listener() {

    @Override
    public void call(Object... args) {}

});
    socket.connect();

}
catch(Exception e){

}

Node.js side

Create normal sockets using socket.io

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