Android socket programming without WIFi connection

Question

I have written an app to start my server at home remotely. The app works without problems in the emulator and also on my smartphone (HTC desire, Android 2.2) when WiFi is enabled. However it does not work when WiFi is disabled.

Before restarting I first check if it's already running. To do this I use sockets and I first connect to a dyndns address. After that I try to connect to my ip-box where I can switch on my computer by sending commands via a socket.

When the connection to that socket fails I know the server is not running.

The relevant code is:

        socket = new Socket();
        socket.connect(new InetSocketAddress(serverName, port), 10000);
            status = socket.isConnected() == true;
        socket.close();

If there's an exception (SocketException) I know that the server is not running. This approach works perfectly when I have switched WiFi on. However if WiFi's not switched on then the connect always says it's ok, even if it could not establish a connection since the server is not available.

Is there a way to check if the the connection is really established, even if WiFi is disabled?

Any suggestions welcome!

Thanks,

Rudi

How do you know that the connection really failed? Even if the WiFi is disabled, a connection may still happen through the cellular data network. See this to make sure that the cellular data network is disabled: newbiehelper.blogspot.com/2011/07/… — Theo
– Theo, Commented Jan 2, 2012 at 1:36
Since the server I am trying to boot is not running it is impossible to establish a connection. When I run the program when wifi is enabled then the call to socket.connect() fails as excepted. I should add that I just found a very similar question on stackoverflow, unfortunately unanswered. Basically the other question refers to problems in 3G-mode, so obviously I am not alone to run into this problem. — Rudolf Ziegaus
– Rudolf Ziegaus, Commented Jan 2, 2012 at 1:42
Ok, so it works with Wifi on, it doesn't work with Wifi off, and this happens on both the emulator and on the real phone? — Theo
– Theo, Commented Jan 2, 2012 at 1:53
This only happens on the real phone, on the emulator I can't switch off Wifi - just tried, since I have never bothered before to switch it off in the emulator. Actually I always assumed sockets should behave the same when run in 3G-mode and in Wifi mode - was a bit naive;-) — Rudolf Ziegaus
– Rudolf Ziegaus, Commented Jan 2, 2012 at 2:04
Your issue seems to be similar to the one in the following thread. Perhaps there's some port filtering on your cell network connection? Try the port 80 suggestion. stackoverflow.com/questions/5749612/… — Theo
– Theo, Commented Jan 2, 2012 at 2:07

Duffydake · Accepted Answer · 2012-01-03 01:34:19Z

2

Try to open your socket like this :

public boolean connect(String ip, int port) {
    try {
        this.clientSocket = new Socket(ip, port);
        clientSocket.setSoTimeout(timeout);
        this.outToServer = new DataOutputStream(clientSocket
                .getOutputStream());
        this.inFromServer = clientSocket.getInputStream();
        isconnected = true;
    } catch (IOException e) {
        Log.e("TCPclient", "connection failed on " + ip + ":" + port);
        isconnected = false;
        return isconnected;
    }
    Log.e("TCPclient", "connection to " + ip + " sucessfull");
    return isconnected;
}

If connection is not successful , it will generate an IOException (work when wifi enabled and no server , and when wifi is not enabled(HTC desire 2.3)).
This code is not really correct ,it's just a short version

EDIT Try to check wfi state like this (it is not practical but it should work)

    public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      ConnectivityManager cm = (ConnectivityManager)  getSystemService(Context.CONNECTIVITY_SERVICE);
      NetworkInfo ni = cm.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
      if (ni.isConnected()) {
        Toast.makeText(this,"Wifi enabled", Toast.LENGTH_LONG).show();  
        Log.d("WiFiStateTestActivity", "WiFi!");
      } else {
        Toast.makeText(this,"Wifi not enabled", Toast.LENGTH_LONG).show();  
        Log.d("WiFiStateTestActivity", "not WiFi!");
      }
    }

edited Jan 3, 2012 at 1:34

answered Jan 2, 2012 at 21:05

Duffydake

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7 Comments

Rudolf Ziegaus Over a year ago

Just tried your code - no change for me. With Wifi enabled I get the exception, when Wifi is disabled, the socket pretends that everything's ok and I get NO exception, even if the server is not running. Which stateement generates the exception in your code? I assume, it's the call to the constructor, right?

Duffydake Over a year ago

Exception come from : this.clientSocket = new Socket(ip, port); W/System.err( 2837): java.net.ConnectException: /192.168.0.1:6789 - Network is unreachable My apps is an apps like yours, but i don't have you problem, my apps run on my HTC désir with no problem and on a android tablet 2.1

Rudolf Ziegaus Over a year ago

For me the samepiece of code fails when Wifi is enabled, so that's what I expected. But I don't understand why you get an exception with wifi disabled and I don't get one - might be the android version, but as I pointed out there's another question regarding the same problem with two different smart phones and two different android versions, so probably it's something different. Sigh - I have got no clue why it does not work.

Duffydake Over a year ago

Maybe you can try to write on socket output, i think it will generate an IOExcption even if you socket indicate that is connected or get wifi state android-er.blogspot.com/2011/01/detect-wifi-onoff-state.html

Rudolf Ziegaus Over a year ago

Nope ... outToServer.writeUTF("test"); ch = inFromServer.read(); the first line passes without problems, the second line returns -1, no exception thrown... Maybe I have to debug the source code of the Socket class to find out the problem underlying...

|

MoIn · Accepted Answer · 2012-04-24 11:02:53Z

1

Don't forget to set the permission in manifest.xml to allow you app to open a socket.

answered Apr 24, 2012 at 11:02

MoIn

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