Web Bluetooth / GAP Characteristics Sample

Available in Chrome 50+ | View on GitHub | Browse Samples

The Web Bluetooth API lets websites discover and communicate with devices over the Bluetooth 4 wireless standard using the Generic Attribute Profile (GATT). It is currently partially implemented in Android M, Chrome OS, Linux, and Mac.

This sample illustrates the use of the Web Bluetooth API to read all GAP characteristics from a nearby Bluetooth Device. You may want to try this demo with the BLE Peripheral Simulator App from the Google Play Store and check out the GAP Characteristics (Async Await) sample.

Note: The Reconnection Address characteristic is blacklisted and forbidden from being accessed.

Live Output


JavaScript Snippet

function onButtonClick() {
  log('Requesting any Bluetooth Device...');
  navigator.bluetooth.requestDevice({
   // filters: [...] <- Prefer filters to save energy & show relevant devices.
      acceptAllDevices: true,
      optionalServices: ['generic_access']})
  .then(device => {
    log('Connecting to GATT Server...');
    return device.gatt.connect();
  })
  .then(server => {
    log('Getting GAP Service...');
    return server.getPrimaryService('generic_access');
  })
  .then(service => {
    log('Getting GAP Characteristics...');
    return service.getCharacteristics();
  })
  .then(characteristics => {
    let queue = Promise.resolve();
    characteristics.forEach(characteristic => {
      switch (characteristic.uuid) {

        case BluetoothUUID.getCharacteristic('gap.appearance'):
          queue = queue.then(_ => readAppearanceValue(characteristic));
          break;

        case BluetoothUUID.getCharacteristic('gap.device_name'):
          queue = queue.then(_ => readDeviceNameValue(characteristic));
          break;

        case BluetoothUUID.getCharacteristic('gap.peripheral_preferred_connection_parameters'):
          queue = queue.then(_ => readPPCPValue(characteristic));
          break;

        case BluetoothUUID.getCharacteristic('gap.central_address_resolution_support'):
          queue = queue.then(_ => readCentralAddressResolutionSupportValue(characteristic));
          break;

        case BluetoothUUID.getCharacteristic('gap.peripheral_privacy_flag'):
          queue = queue.then(_ => readPeripheralPrivacyFlagValue(characteristic));
          break;

        default: log('> Unknown Characteristic: ' + characteristic.uuid);
      }
    });
    return queue;
  })
  .catch(error => {
    log('Argh! ' + error);
  });
}

function readAppearanceValue(characteristic) {
  return characteristic.readValue().then(value => {
    log('> Appearance: ' +
        getDeviceType(value.getUint16(0, true /* Little Endian */)));
  });
}

function readDeviceNameValue(characteristic) {
  return characteristic.readValue().then(value => {
    log('> Device Name: ' + new TextDecoder().decode(value));
  });
}

function readPPCPValue(characteristic) {
  return characteristic.readValue().then(value => {
    log('> Peripheral Preferred Connection Parameters: ');
    log('  > Minimum Connection Interval: ' +
        (value.getUint8(0) | value.getUint8(1) << 8) * 1.25 + 'ms');
    log('  > Maximum Connection Interval: ' +
        (value.getUint8(2) | value.getUint8(3) << 8) * 1.25 + 'ms');
    log('  > Slave Latency: ' +
        (value.getUint8(4) | value.getUint8(5) << 8) + 'ms');
    log('  > Connection Supervision Timeout Multiplier: ' +
        (value.getUint8(6) | value.getUint8(7) << 8));
  });
}

function readCentralAddressResolutionSupportValue(characteristic) {
  return characteristic.readValue().then(value => {
    let supported = value.getUint8(0);
    if (supported === 0) {
      log('> Central Address Resolution: Not Supported');
    } else if (supported === 1) {
      log('> Central Address Resolution: Supported');
    } else {
      log('> Central Address Resolution: N/A');
    }
  });
}

function readPeripheralPrivacyFlagValue(characteristic) {
  return characteristic.readValue().then(value => {
    let flag = value.getUint8(0);
    if (flag === 1) {
      log('> Peripheral Privacy Flag: Enabled');
    } else {
      log('> Peripheral Privacy Flag: Disabled');
    }
  });
}

/* Utils */

function getDeviceType(value) {
  // Check out page source to see what valueToDeviceType object is.
  return value +
      (value in valueToDeviceType ? ' (' + valueToDeviceType[value] + ')' : '');
}