c# - Pair bluetooth devices to a computer with 32feet .NET Bluetooth library

Question

If you want to know how to use 32feet.NET library to communicate with bluetooth devices, read the solution

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I am currently trying to communicate via bluetooth between a computer and a self-built .NET Gadgeteer prototype.

The Gadgeteer prototype consists of the mainboard, a power supply and a bluetooth module. The module is in discoverable mode.

On the computer a custom bluetooth program based on 32feet .NET Bluetooth is running. The program detects all bluetooth devices in range and tries to pair with them. However, this is not done automatically at the moment, I have to enter a pairing code for the device.

How can I pair devices without entering the pairing code?

Devices are found, the problem is the pairing part. I experimented a lot, but didn't find a solution...

foreach (BluetoothDeviceInfo device in this.deviceList)
{
    try
    {
        //BluetoothClient client = new BluetoothClient(this.CreateNewEndpoint(localAddress));
        //BluetoothEndPoint ep = this.CreateNewEndpoint(device.DeviceAddress);

        EventHandler<BluetoothWin32AuthenticationEventArgs> handler = new EventHandler<BluetoothWin32AuthenticationEventArgs>(HandleRequests);
        BluetoothWin32Authentication auth = new BluetoothWin32Authentication(handler);

        BluetoothSecurity.PairRequest(device.DeviceAddress, null);
    }
}

This code block initiates the pairing and it works, but Windows is asking me to enter the pairing code for the device. I read about the BluetoothWin32Authentication to prevent this case but I don't get it right.

private void HandleRequests(object that, BluetoothWin32AuthenticationEventArgs e)
{
    e.Confirm = true;
}

This is the code of the event handler (http://32feet.codeplex.com/wikipage?title=BluetoothWin32Authentication)

If you simply want to allow the pairing to go ahead when to SSP devices are connecting then handling the callback and setting e.Confirm=True will be enough -- but that is a little insecure...

---

I am confused -.- The goal is that the application and the gadgeteer module can send data in both directions without any user interference.

Is it true that I can't pair devices automatically without user interaction?

Is it true that if two device were already paired they can exchange data without user interaction?

Answer 1

I figured out how to solve my problems and my knowledge about Bluetooth connections is a bit bigger now. If someone else has problems with that, I provide my solution. The code examples represent the C# implementation of a bluetooth controller with the 32feet Bluetooth library.

Scanning

This means that devices in range are detected. My code:

// mac is mac address of local bluetooth device
BluetoothEndPoint localEndpoint = new BluetoothEndPoint(mac, BluetoothService.SerialPort);
// client is used to manage connections
BluetoothClient localClient = new BluetoothClient(localEndpoint);
// component is used to manage device discovery
BluetoothComponent localComponent = new BluetoothComponent(localClient);
// async methods, can be done synchronously too
localComponent.DiscoverDevicesAsync(255, true, true, true, true, null);
localComponent.DiscoverDevicesProgress += new EventHandler<DiscoverDevicesEventArgs>(component_DiscoverDevicesProgress);
localComponent.DiscoverDevicesComplete += new EventHandler<DiscoverDevicesEventArgs>(component_DiscoverDevicesComplete);

private void component_DiscoverDevicesProgress(object sender, DiscoverDevicesEventArgs e)
{
    // log and save all found devices
    for (int i = 0; i < e.Devices.Length; i++)
    {           
        if (e.Devices[i].Remembered)
        {
            Print(e.Devices[i].DeviceName + " (" + e.Devices[i].DeviceAddress + "): Device is known");
        }
        else
        {
            Print(e.Devices[i].DeviceName + " (" + e.Devices[i].DeviceAddress + "): Device is unknown");
        }
        this.deviceList.Add(e.Devices[i]);         
    }
}

private void component_DiscoverDevicesComplete(object sender, DiscoverDevicesEventArgs e)
{
    // log some stuff
}

Pairing

This means that devices get coupled with the local bluetooth device. This needs to be done once by entering a code of both sides. Can be done via code so that the user doesn't even notice that a device was added. My code for this purpose:

// get a list of all paired devices
BluetoothDeviceInfo[] paired = localClient.DiscoverDevices(255, false, true, false, false);
// check every discovered device if it is already paired 
foreach (BluetoothDeviceInfo device in this.deviceList)
{
    bool isPaired = false;
    for (int i = 0; i < paired.Length; i++)
    {
        if (device.Equals(paired[i]))
        {
            isPaired = true;
            break;
        }
    }

    // if the device is not paired, pair it!
    if (!isPaired)
    {
        // replace DEVICE_PIN here, synchronous method, but fast
        isPaired = BluetoothSecurity.PairRequest(device.DeviceAddress, DEVICE_PIN);
        if (isPaired)
        {
            // now it is paired
        }
        else
        {
            // pairing failed
        }
    }
}

Connecting

This means establishing a connection and exchanging of data. Again some code:

// check if device is paired
if (device.Authenticated)
{
    // set pin of device to connect with
    localClient.SetPin(DEVICE_PIN);
    // async connection method
    localClient.BeginConnect(device.DeviceAddress, BluetoothService.SerialPort, new AsyncCallback(Connect), device);
}

// callback
private void Connect(IAsyncResult result)
{
    if (result.IsCompleted)
    {
        // client is connected now :)
    }
}

If you keep the order scan, pair, connect, everything should work fine. To send or receive data, use the GetStream() method of the BluetoothClient. It provides a network stream that can be manipulated.

Receiving a connection

If you want another device to connect with your device you need to listen to incoming connection requests. This only works if the device have already been paired before. My code:

BluetoothListener l = new BluetoothListener(LOCAL_MAC, BluetoothService.SerialPort);
l.Start(10);
l.BeginAcceptBluetoothClient(new AsyncCallback(AcceptConnection), l);

void AcceptConnection(IAsyncResult result){
    if (result.IsCompleted){
        BluetoothClient remoteDevice = ((BluetoothListener)result.AsyncState).EndAcceptBluetoothClient(result);    
    }    
}

Replace LOCAL_MAC with a valid BluetoothAddress (e.g. by using BluetoothAddress.Parse();). After the devices are connected they can exchange messages via the underlying stream. If the connection does not work there might be authentication issues, so try setting the local device pin in the listener (l.SetPin(LOCAL_MAC, MY_PASSWORD);