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IoT Bluetooth Smart Peripheral API

Introduction

This API exposes Bluetooth Smart functionality for Bluetooth Smart Peripheral (BSP) mode. The terminology and context is taken from the Bluetooth 4.2. specification.

A Bluetooth Smart Peripheral (BSP) device supports the following functionality:

  • Host a GATT (Generic Attribute Profile) server that exposes a hierarchy of Service, Characteristic and Descriptor objects.
  • Broadcast (advertise) information (e.g. services) using advertisement packets. Advertisement or Scan Response data packet is a 31 byte payload used to advertise the device's capabilities and connection parameters.
  • Accept connections from Bluetooth Smart devices in Central mode that can access its services exposed through the the Generic Access Profile (GAP). A device has only one instance of the GAP service in the GATT server. The GAP service is a GATT based service with the service UUID as «GAP Service» defined in the Bluetooth Assigned Numbers document.

The W3C Web Bluetooth API exposes functionality for Bluetooth Smart clients (Central mode).

Use cases

This API is used by applications that implement a Bluetooth Peripheral device and expose sensor data via Bluetooth.

  • Applications define the Bluetooth Smart services, characteristics and descriptors, then register them with the implementation.
  • Applications can build Bluetooth advertisement packets, then start and stop advertising.
  • For the defined characteristics, applications should register event listeners for handling requests coming from clients. The event listeners receive the request, and should reply to them with appropriate data, or with an error code.
The API object -------------- The API entry point is a [`BluetoothPeripheralDevice`](./#bpd) object that is exposed in a platform-specific manner. As an example, on Node.js it can be obtained by requiring the package that implements this API. On other platforms, it can be constructed. 
var btdevice = require('bluetooth-peripheral');

If the functionality is not supported by the platform, require should throw NotSupportedError. If the underlying platform doesn't allow using the functionality, require should throw SecurityError.

 ### The `BluetoothPeripheralDevice` interface This object is created and returned by `require`. It has the following read-only properties:
Property Type Optional Default value Represents
address String no undefined Bluetooth Device Address
addressType String enum no undefined Bluetooth Device Address Type
name String yes undefined the Bluetooth Device Name in scan responses
enabled boolean no false whether Bluetooth is enabled
services array of service objects no [] Primary services on the device
version string no version inpackage.json API version
Event name Event callback argument
statechange N/A
connect String (client Bluetooth Device Address)
disconnect String (client Bluetooth Device Address)
error Error
Method signature Description
enable() enable the device
disable() disable the device
startAdvertising(advertisement, options) start sending advertisment packets
stopAdvertising() stop sending advertisment packets
addService(service) add a service object to the device
removeService(service) remove a service object

BluetoothPeripheralDevice properties

The `address` property is a 48 bit value (BD_ADDR) identifying a Bluetooth Smart device. On the UI level, the Bluetooth address MUST be represented as 12 hexadecimal characters, possibly divided into sub-parts separated by ‘:’ (e.g., ‘000C3E3A4B69’ or ‘00:0C:3E:3A:4B:69’). On the UI level, any number MUST have the most significant bit on left ordering. The `addressType` property can take the following values: `"public"`, `"static-random"`, `"private-resolvable"`, and `"private"`. The `name` property represents the Bluetooth device name that a Bluetooth device exposes to remote devices. It is up to 248 bytes encoded as UTF-8, therefore on the UI level it may be restricted to as few as 62 characters if codepoints outside the range U+0000 to U+007F are used. A device cannot expect that a general remote device is able to handle more than the first 40 characters of the Bluetooth device name. If a remote device has limited display capabilities, it may use only the first 20 characters. The `enabled` property MUST be set to `true` if the Bluetooth Smart functionality is enabled on the device, and otherwise to `false`. The `services` property is a read-only array (sequence) of [`BluetoothService`](#service) objects that represents the primary GATT services on the device. A primary service is visible at device root level, and it may contain other services.

The version property is read-only, and provides the master API version, as specified in the version property of package.json.

BluetoothPeripheralDevice events

The statechange event is emitted when the enabled property is changed. Event listeners are called with no parameters and should check the value of the enabled property.

The connect event is emitted when a Bluetooth Smart device in Central mode (client) is connected. Event listeners are invoked with the client's Bluetooth Device Address as a string argument.

The disconnect event is emitted when a connected client device is disconnected. Event listeners are invoked with the client's Bluetooth Device Address as a string argument.

The error event is emitted when a Bluetooth error needs to be reported to the application. Event listeners are invoked with an Error object as argument.

BluetoothPeripheralDevice methods

The enable() method

Requests enabling the device, and Bluetooth Smart functionality if needed, then returns. When the device is enabled, implementations should set the enabled property to true and emit the statechange event.

The disable() method

Requests disabling the device, then returns. When the device is disabled, implementations should set the enabled property to false and emit the statechange event.

The startAdvertising(advertisement, options) method

Requests the platform to send Bluetooth Smart advertising packets initialized from the arguments.

The options argument

It is an object with the following properties:

Property Type Optional Default value Represents
connectable boolean yes true whether the device can be connected to
minInterval Number yes selected by the platform minimum time interval between advertisements
maxInterval Number yes selected by the platform maximum time interval between advertisements

The connectable advertisement option is true when the device is allowed to be connected by clients.

The minInterval advertisement option tells the minimum time interval between consecutive advertisement packets in milliseconds. The value can be between 100 and 32000 milliseconds. Platforms may override this value.

The maxInterval advertisement option tells the maximum time interval between consecutive advertisement packets in milliseconds. The value can be between 100 and 32000 milliseconds. Platforms may override this value.

The advertisement argument

Advertisement packet data can be of the following types: string (e.g. flags), device name, transmit power, service UUID (16, 32, or 128 bit), service data, public or random target address, advertising interval, device address, Bluetooth Smart role, URI, or manufacturer data. Applications are expected to build the binary advertisement packets based on the Bluetooth specifications as a Buffer object. This API provides helpers for the most common data types. It is an object with properties described in the startadvertising() method steps.

The startadvertising() method runs the following steps:

  • Return a Promise object promise and continue in parallel.
  • If options.connectable is not true, then set options.connectable to false.
  • If options.minInterval is undefined, set options.minInterval to a platform default value. Otherwise, if it is a number, and it is smaller than 100 or bigger than 32000, reject promise with TypeError. Otherwise, set options.minInterval to that value rounded down to the nearest value divisible by 100.
  • If options.maxInterval is undefined, set options.maxInterval to a platform default value. Otherwise, if it is a number, and it is smaller than 100 or bigger than 32000, reject promise with TypeError. Otherwise, set options.maxInterval to that value rounded down to the nearest value divisible by 100.
  • If advertisement is not an object, reject promise with TypeError.
  • If advertisement.scanResponse is an object and advertisement.scanResponse.name is a string or advertisement.scanResponse.date is a Buffer object, then let scanResponse be advertisement.scanResponse.
  • If advertisement.data is a Buffer object, let buffer take that value.
  • Otherwise, let buffer be an empty Buffer, and use the properties of advertisement (when defined) to prepare buffer based on the following properties of advertisement. The algorithm on how to prepare buffer is described in the Bluetooth specification, and the platform may have an API to support that.
    • uuids is an array of Bluetooth UUID strings representing services; if specified, implementations SHOULD add them to the advertisement packet buffer compliant to the Bluetooth specification.
    • serviceData is an object with two properties, a UUID string uuid and a Buffer object data. Implementations should add uuid and data to buffer, if there is sufficient space in the advertisement packet. If there is not sufficient space, skip to the next step.
    • manufacturerData is an object with two properties, a number manufacturerId and a Buffer data. Implementations should add manufacturerId and data to buffer, if there is sufficient space in the advertisement packet. If there is not sufficient space, skip to the next step.
    • deviceClass is a number. If specified, implementations should add it to buffer, if there is sufficient space in the advertisement packet. If there is not sufficient space, skip to the next step.
    • includeTxPower is a boolean value. If true, then implementations should add the transmit power to the advertisement packet, if there is space. If not, skip to the next step.
  • Request the underlying platform to start sending the prepared advertisement packet buffer with the options specified in options. If the request fails, reject promise with an Error object error that has error.message set to "BluetoothStartAdvertisement".
  • If the implementation can read the advertisement options used by the platform for this advertisement, set options.minInterval and options.maxInterval to the actual values used by the platform.
  • Resolve promise with options.

The stopAdvertising() method

Requests the platform to stop sending advertisement packets. It runs the following steps:

  • Request from the underlying platform to stop the current advertisement.
  • If the request is unsuccessful, throw an Error object error with error.message set to "BluetoothStopAdvertisement".

The addService(service) method

Adds a service to the internal slot representing the primary services. Returns false if service is not a valid BluetoothService object, or if service.primary is false, or if service.uuid has already been added.

The removeService(service, recursive) method

Removes a service from the internal slot that represents the primary services of the device. Returns false if service is not a valid BluetoothService object, or if service.uuid is not found in the internal slot of Bluetooth services. If recursive is true, then also removes all services in service.includedServices that are not used by any other service.

The BluetoothService dictionary

It is an object with the following properties:

Property Type Optional Default value Represents
uuid String no undefined Bluetooth Service UUID
primary boolean no false whether primary (root) service
characteristics array of BluetoothCharacteristic objects no [] Bluetooth characteristics
includedServices array of String no [] list of UUIDs of included services

The BluetoothDescriptor dictionary

It is an object with the following properties:

Property Type Optional Default value Represents
uuid String no undefined Bluetooth Descriptor UUID
value String no undefined descriptor value
flags array of String no [] flags (Bluetooth "properties")

The flags property contains a maximum of 2 strings that can be either "read" or "write".

The BluetoothCharacteristic interface

It has the following read-only properties:

Property Type Optional Default value Represents
uuid String no undefined Bluetooth Descriptor UUID
flags array of String no [] flags (Bluetooth "properties")
descriptors array of objects no [] Bluetooth descriptors
notifying boolean no undefined whether notifications are on
Method signature Description
startNotifications() turn on notifications
stopNotifications() turn off notifications
onread(handler) registers callback for handling read requests
onwrite(handler) registers callback for handling write requests
onsubscribe(handler) registers callback for handling subscribe requests
onunsubscribe(handler) registers callback for handling unsubscribe requests
onerror(handler) registers error handler

The BluetoothCharacteristic object can be constructed with a dictionary that can have any or all of the following properties of BluetoothCharacteristic: uuid, flags, descriptors.

BluetoothCharacteristic properties

The uuid property is a string that represents a Bluetooth UUID.

The flags property is an array of strings that can take the following values: "read", "write", "notify".

The descriptors property is an array of BluetoothDescriptor objects that describe this Bluetooth Characteristic.

The notifying property is a boolean that is true when notifications are turned on and false otherwise.

BluetoothCharacteristic methods

The startNotifications() method

Requests the underlying platform to start sending notifications for this characteristic to all subscribed clients.

The stopNotifications() method

Requests the underlying platform to stop sending notifications for this characteristic.

The onread(handler) method

Registers a function to handle read requests for the Characteristic. The handler argument is a function that accepts a BluetoothCharacteristicRequest argument.

The onwrite(handler) method

Registers a function to handle write requests for the Characteristic. The handler argument is a function that accepts a BluetoothCharacteristicRequest argument.

The onsubscribe(handler) method

Registers a function to handle subscribe requests for the Characteristic. The handler argument is a function that accepts a BluetoothCharacteristicRequest argument.

The onunsubscribe(handler) method

Registers a function to handle unsubscribe requests for the Characteristic. The handler argument is a function that accepts a BluetoothCharacteristicRequest argument.

The onerror(handler) method

Registers a function to handle Bluetooth errors concerning operations with Characteristics that need to be reported to the application. The handler argument is a function that accepts an Error object as argument.

The BluetoothCharacteristicRequest interface

Contains the following read-only properties:

Property Type Optional Default value Represents
type String no undefined request type
source String no undefined client Bluetooth Device Address
data Buffer yes null data
offset number yes 0 Offset in data
needsResponse boolean yes true whether response needs to be sent
Method signature Description
respond(data) send a response with data
respondWithError(error) send an error response

BluetoothCharacteristicRequest properties

The type property is a string that can take one of the following values: "read", "write", "notify", "subscribe", "unsubscribe".

The source property is a string representing the Bluetooth Device Address of the client.

The data property is a Buffer object that is not null for "write" operation, and null otherwise.

The offset property is a positive number that specifies the byte offset in data pertaining to the operation (read or write).

The needsResponse property is a boolean that is by default true.

BluetoothCharacteristicRequest methods

The respond(data) method

Sends a response to the request. It executes the following steps:

  • Create a response to the request, and include data in the response.
  • Request from the underlying platform to send the response to the client.
  • If the request is unsuccessful, throw an Error object error with error.message set to "BluetoothSendResponse".

The error(error) method

Sends an error response to the request. It executes the following steps:

  • Create an error response to the request, and include error in the response.
  • Request from the underlying platform to send the response to the client.
  • If the request is unsuccessful, throw an Error object error with error.message set to "BluetoothSendErrorResponse".