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

android, android-asynctask, android-networking, java

Solution

Network connection / Internet access

- `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 2018 it handled over a trillion queries a day [1]. Let 's just say, your app would probably not be the talk of the day.

Which permissions are required?

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

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 `RxJava/RxAndroid` Example (Kotlin)

fun hasInternetConnection(): Single<Boolean> {
  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 */}

Extra: One-shot `RxJava/RxAndroid` Example (Java)

public static Single<Boolean> hasInternetConnection() {
    return Single.fromCallable(() -> {
        try {
            // Connect to Google DNS to check for connection
            int timeoutMs = 1500;
            Socket socket = new Socket();
            InetSocketAddress socketAddress = new InetSocketAddress("8.8.8.8", 53);

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

            return true;
        } catch (IOException e) {
            return false;
        }
    }).subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread());
}

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

    hasInternetConnection().subscribe((hasInternet) -> {
        if(hasInternet) {

        }else {

        }
    });

Extra: One-shot `AsyncTask` Example

Caution: This shows another example of how to do the request. However, since `AsyncTask` is deprecated, it should be replaced by your App's thread scheduling, Kotlin Coroutines, Rx, ...

class InternetCheck extends AsyncTask<Void,Void,Boolean> {

    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 */ });

Problem

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<String, Void, Boolean> { 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(); } } ```

Original source

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