networking - How to check internet access on Android? InetAddress never times out

I got a AsyncTask that is supposed to check the network access to a host name. But the doInBackground() is never timed out. Anyone have a clue?

public class HostAvailabilityTask extends AsyncTask {

    private Main main;

    public HostAvailabilityTask(Main main) {
        this.main = main;
    }

    protected Boolean doInBackground(String... params) {

        Main.Log("doInBackground() isHostAvailable():"+params[0]);

        try {
            return InetAddress.getByName(params[0]).isReachable(30); 
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return false;       

    }

    protected void onPostExecute(Boolean... result) {
        Main.Log("onPostExecute()");

        if(result[0] == false) {
            main.setContentView(R.layout.splash);
            return;
        }


        main.continueAfterHostCheck();
    }   
}

Answer

• isConnectedOrConnecting() (used in most answers) checks for any network connection


• To know whether any of those networks have internet access, use one of the following

A) Ping a Server (easy)

// ICMP 
public boolean isOnline() {
    Runtime runtime = Runtime.getRuntime();
    try {
        Process ipProcess = runtime.exec("/system/bin/ping -c 1 8.8.8.8");
        int     exitValue = ipProcess.waitFor();

        return (exitValue == 0);
    }
    catch (IOException e)          { e.printStackTrace(); }
    catch (InterruptedException e) { e.printStackTrace(); }

    return false;
}

+ could run on main thread

- does not work on some old devices (Galays S3, etc.), it blocks a while if no internet is available.

B) Connect to a Socket on the Internet (advanced)

// TCP/HTTP/DNS (depending on the port, 53=DNS, 80=HTTP, etc.)
public boolean isOnline() {
    try {
        int timeoutMs = 1500;
        Socket sock = new Socket();

        SocketAddress sockaddr = new InetSocketAddress("8.8.8.8", 53);

        sock.connect(sockaddr, timeoutMs);
        sock.close();

        return true;
    } catch (IOException e) { return false; }
}

+ very fast (either way), works on all devices, very reliable

- can't run on the UI thread

This works very reliably, on every device, and is very fast. It needs to run in a separate task though (e.g. ScheduledExecutorService or AsyncTask).

Possible Questions

• Is it really fast enough?

  
  
  
  

  Yes, very fast ;-)




• Is there no reliable way to check internet, other than testing something on the internet?

  
  
  

  Not as far as I know, but let me know, and I will edit my answer.




• What if the DNS is down?

  
  
  

  Google DNS (e.g. 8.8.8.8) is the largest public DNS in the world. As of 2013 it served 130 billion requests a day. Let 's just say, your app would probably not be the talk of the day.




• Which permissions are required?

  
  
  
  
  
  
  

  Just internet access - surprise ^^ (Btw have you ever thought about, how some of the methods suggested here could even have a remote glue about internet access, without this permission?)

Extra: One-shot AsyncTask Example

class InternetCheck extends AsyncTask {

    private Consumer mConsumer;
    public  interface Consumer { void accept(Boolean internet); }

    public  InternetCheck(Consumer consumer) { mConsumer = consumer; execute(); }

    @Override protected Boolean doInBackground(Void... voids) { try {
        Socket sock = new Socket();
        sock.connect(new InetSocketAddress("8.8.8.8", 53), 1500);

        sock.close();
        return true;
    } catch (IOException e) { return false; } }

    @Override protected void onPostExecute(Boolean internet) { mConsumer.accept(internet); }
}

///////////////////////////////////////////////////////////////////////////////////
// Usage


    new InternetCheck(internet -> { /* do something with boolean response */ });

Extra: One-shot RxJava/RxAndroid Example (Kotlin)

fun hasInternetConnection(): Single {
  return Single.fromCallable {
    try {
      // Connect to Google DNS to check for connection
      val timeoutMs = 1500

      val socket = Socket()
      val socketAddress = InetSocketAddress("8.8.8.8", 53)

      socket.connect(socketAddress, timeoutMs)
      socket.close()

      true
    } catch (e: IOException) {
      false
    }

  }
  .subscribeOn(Schedulers.io())
  .observeOn(AndroidSchedulers.mainThread())
}

///////////////////////////////////////////////////////////////////////////////////
    // Usage

    hasInternetConnection().subscribe { hasInternet -> /* do something */}