Hidden Android APIs: listening to incoming SMS messages

In the Android platform there are two classes, SmsManager and SmsMessage, for sending SMS messages; hower there is no official class for receiving them. To be able to receive SMS messages we have to use a hidden API, present in the Android platform but not generally available for developers.

Hidden Android APIs contain several constants, methods, interfaces, etc. that can come in handy in a variety of situations.

To discover hidden Android APIs you can use the following resource:

• AndroidXRef (http://androidxref.com): this site has indexed all the Android source code and offers a useful search box; however you have to know exactly what you are looking for.

Searching class Telephony from AndroidXRef

In order to make use of the Android hidden APIs, there are two possible scenarios:

• constants: if you just need to use a hidden constant (for example for broacast actions), you can simply copy them from the Android source code into your app. In this tutorial we will use this technique;
• methods, classes, interfaces, etc.: hidden methods, classes and interfaces must be compiled, before beeing able to use them. To do this you can either modify the SDK jar file used to compile your app, or make use of the java reflection method, each of which has its pros and cons.

To be able to receive incoming SMS messages we will use the following hidden constants contained in the class telephony-common (you can find them using the utilities listed above):

• “android.provider.Telephony.SMS_RECEIVED”: Intent action used in our BroadcastReceiver to listen to incoming SMS messages;
• “pdus”: constant used to retrieve SMS data from the Intent.

Extract from the class Telephony of the Android source code

Extract from the class Telephony of the Android source code

So here is the code:

1. declare the use of the RECEIVE_SMS permission in the AndroidManifest.xml file;
2. declare a BroadcastReceiver in the AndroidManifest.xml file with the intent-filter “android.provider.Telephony.SMS_RECEIVED”;
3. implement the BroadcastReceiver as follows:

public class SMSReceiver extends BroadcastReceiver {

 public void onReceive(Context context, Intent intent) {
  String action = intent.getAction();

  if(action.equals(“android.provider.Telephony.SMS_RECEIVED”)) {
   Object incomingSMSs[] = (Object[]) intent.getSerializableExtra(“pdus”);
   
   for(Object tmp : incomingSMSs) {
    byte message[] = (byte[]) tmp;
    SmsMessage smsMessage = SmsMessage.createFromPdu(message);
   }
  }
 }
}

Once you have a SmsMessage object, you can use one ot its several methods to retrieve useful info about the SMS received:

smsMessage.getOriginatingAddress();
smsMessage.getMessageBody();
etc.