CODEWITHSUNDEEP
javascriptbluetoothbluetooth-lowenergyweb-bluetooth
Paul
Paul

Reputation: 21

ENABLE_NOTIFICATION_VALUE - Web Bluetooth API

Client Configuration Characteristic Descriptor (CCCD).

UUID - "00002902-0000-1000-8000-00805f9b34fb" / 'gatt.client_characteristic_configuration'.

To set CCCD in Java code for Android we do:

public static final byte[] ENABLE_NOTIFICATION_VALUE = {0x01, 0x00};

BluetoothGattDescriptor descriptor =    characteristic.getDescriptor("00002902-0000-1000-8000-00805f9b34fb");
descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
mBluetoothGatt.writeDescriptor(descriptor);

How can I perform a similar configuration in JavaScript code when using the Web Bluetooth API ?

My version in JavaScript: 

.then(descriptors => {    
let queue = Promise.resolve();
 descriptors.forEach(descriptor => {
        switch (descriptor.uuid) {    
          case BluetoothUUID.getDescriptor('gatt.client_characteristic_configuration'):
           queue = queue.then(_ => descriptor.readValue()).then(value => {
              descriptorCache = descriptor;
            });
   ...

    var data = new Uint8Array([0x01, 0x00]);
    descriptorCache.writeValue(data);
    //descriptorCache.writeValue(new TextEncoder().encode(data));

fails with a security error :-(

Uncaught (in promise) DOMException: writeValue() called on blocklisted object marked exclude-writes. https://webbluetoothcg.github.io/web-bluetooth/#attacks-on-devices

I understand the need for security. But after all, a lot of devices require a presetting of the CCCD.

Upvotes: 2

Views: 1061

Answers (1)

Jeffrey Yasskin
Jeffrey Yasskin

Reputation: 5682

Calling characteristic.StartNotifications() sets the CCCD for you.

Upvotes: 2

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