Matt Matt - 5 months ago 46
Android Question

"Service discovery failed" from Android Bluetooth Insecure Rfcomm

Does anyone know how to create an insecure RFCOMM connection between 2 Android devices at API level 2.3.3 while using an arbitrarily declared service name? (not random or changing service name, just a service name that I define myself)

Details



I am trying to create an insecure Rfcomm connection between 2 Android devices: Droid X2 and an Asus Transformer. I am assuming that both of these devices have functionality at the level of Android 2.3.3 to actually gain the ability to use insecure Rfcomm.

When I try to create the Bluetooth connection as described here, using the now public createInsecureRfcommSocketToServiceRecord() and listenUsingInsecureRfcommWithServiceRecord(SERVICE, UUID), I get a reported:

java.io.IOException: Service discovery failed
at android.bluetooth.BluetoothSocket$SdpHelper.doSdp(BluetoothSocket.java:377)
at android.bluetooth.BluetoothSocket.connect(BluetoothSocket.java:201)
at com.s4d.bluenomad.DeviceConnections$ClientThread.run(DeviceConnections.java:406)


I found a related question where someone creating a normal connection was getting this error and used reflection to invoke a private method. However, I have no idea what private method would now correspond to initiating an "insecure" connection. I tried using the solution proposed in that related question, but I am asked by Android to pair the devices which is exactly what I need to avoid. I really do need the insecure approach.

I even tried a combination of the official and hacked solutions outlined here

Relevant Code Snippets



Creating ServerThread To Listen For Connections

Log.i(TAG, "Constructing a ServerThread");
// Use a temporary object that is later assigned to serverSocket,
// because serverSocket is final
BluetoothServerSocket tmp = null;
try {
// MY_UUID is the app's UUID string, also used by the client code
tmp = btAdapter.listenUsingInsecureRfcommWithServiceRecord(SERVICE_NAME, SERVICE_UUID);
Log.i(TAG,"Started listening on insecure RFCOMM channel for service requests for: " + SERVICE_NAME);
} catch (IOException e) { }
serverSocket = tmp;


ServerThread Listening for Connections

BluetoothSocket socket;
while(true)
{
try
{
socket = serverSocket.accept();
}
catch( IOException e)
{
break;
}

if( socket != null )
{
Log.i(TAG, "Received new socket connection requesting service: " + SERVICE_NAME);
}
else
{
Log.i(TAG, "Socket connection attempted, but socket received is NULL.");
}
}


Creating ClientThread to Initiate Connections

Log.i(TAG, "Constructing a ClientThread");
BluetoothSocket tmp = null;
try {
// MY_UUID is the app's UUID string, also used by the server code
tmp = device.createInsecureRfcommSocketToServiceRecord(SERVICE_UUID);
Log.i(TAG,"Created client socket on insecure RFCOMM channel for service requests for: " + SERVICE_NAME);
}
catch (IOException e)
{
Log.i(TAG, "Failed to createInsecureRfcommSocket() against MAC: " + device.getAddress());
}
clientSocket = tmp;


ClientThread Connecting to Server

try
{
clientSocket.connect();
}
catch( final IOException e)
{
DeviceConnections.this.runOnUiThread(new Runnable()
{

@Override
public void run()
{
console.append("Client unable to connect to service.");
Log.i(TAG, "Client socket unable to connect() to: " + clientSocket.getRemoteDevice().getAddress());
e.printStackTrace();
}

});

}


I do get the log output "Client socket unable to connect() to: [MY_MAC_ADDRESS]", then I get the stacktrace for the "Service discovery failed" exception.

Answer

It appears the problem was that before I called

clientSocket.connect()

I needed to call

btAdapter.cancelDiscovery()

I had seen this in documentation but it was listed as a "performance" issue - in my case it seems that this was actually a "functional" issue. Once I added the cancel discovery call, the socket connection worked immediately.