B2G/Bluetooth/WebBluetooth-v2/BluetoothGattCharacteristic

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Overview

BluetoothGattCharacteristic represents the characteristic of services. BluetoothGattCharacteristic consists of the characteristic definition, a characteristic value along with properties and configurations which indicate how to access the value, and a list of descriptors which provides related information of this characteristic value.

Interfaces

BluetoothGattCharacteristic

[CheckPermissions="bluetooth"]
interface BluetoothGattCharacteristic
{ 
  readonly attribute BluetoothGattService service;
  [Cached, Pure] readonly attribute sequence<BluetoothGattDescriptor> descriptors;

  readonly attribute DOMString uuid;
  readonly attribute unsigned short instanceId;
  readonly attribute ArrayBuffer? value;
  [Cached, Constant] readonly attribute GattPermissions permissions;
  [Cached, Constant] readonly attribute GattCharacteristicProperties properties;
  [Cached, Pure]              attribute WriteType writeType;

  [NewObject] Promise<ArrayBuffer> readValue();
  [NewObject] Promise<void> writeValue(ArrayBuffer value);
  [NewObject] Promise<void> startNotifications();
  [NewObject] Promise<void> stopNotifications();
  [NewObject] Promise<BluetoothGattDescriptor> addDescriptor(DOMString uuid, GattPermissions permissions, ArrayBuffer value);
};

GattPermissions

dictionary GattPermissions
{
  boolean read = false;
  boolean readEncrypted = false;
  boolean readEncryptedMITM = false;
  boolean write = false;
  boolean writeEncrypted = false;
  boolean writeEncryptedMITM = false;
  boolean writeSigned = false;
  boolean writeSignedMITM = false;
};

GattCharacteristicProperties

dictionary GattCharacteristicProperties
{
  boolean broadcast = false;
  boolean read = false;
  boolean writeNoResponse = false;
  boolean write = false;
  boolean notify = false;
  boolean indicate = false;
  boolean signedWrite = false;
  boolean extendedProps = false;
};

WriteType

dictionary WriteType
{
  required boolean noResponse;
  required boolean default;
  required boolean signed;
};

GattCharacteristicProperties

service

Description
The service which this characteristic belongs to.
Value Type
BluetoothGattService
Default Value
null pointer

descriptors

Description
A cached descriptor array of this characteristic.
Value Type
sequence<BluetoothGattDescriptor>
Default Value
Empty array (array with length = 0)

uuid

Description
This property stores the UUID of this characteristic.
Value Type
DOMString
Default Value
Empty string ("")

instanceId

Description
This property stores the instance id of this characteristic.
Value Type
unsigned short
Default Value
0

value

Description
The cached value of this characteristic. This value can be updated via readValue() method or via characteristic notification or indication from the remote device.
Value Type
ArrayBuffer or null
Default Value
null pointer

permissions

Description
A bit mask which describes allowed operations on the characteristic.
Value Type
dictionary GattPermissions
Default Value
0

properties

Description
A bit mask which describes how to use the characteristic value.
Value Type
dictionary GattCharacteristicProperties
Default Value
0

writeType

Description
The type of write operation.
Value Type
dictionary WriteType
Default Value
0

Methods

readValue()

Description
Read the characteristic value from either remote device (client role) or the local device (server role). In client mode, the cached value property will also be updated after retrieving the value from the remote GATT server.
Return
A Promise to indicate whether the operation is resolved or rejected. The Promise is resolved along with the value retrieved from the remote device or local device.

writeValue(ArrayBuffer value)

Description
Write the characteristic value to the GATT server. If the local device is the GATT client, the value will be written to the remote GATT server. On the other hand, if the local device is the GATT server, the value will be written to value.
Parameter
value
Desired value to be written to the GATT server.
Return
A Promise to indicate whether the operation is resolved or rejected.

startNotifications()

Description
Register notification/indication of this characteristic.
Return
A Promise to indicate whether the operation is resolved or rejected. The Promise is rejected if there is no Client Characteristic Configuration descriptor (CCCD) for this characteristic.

stopNotifications()

Description
Unregister notification/indication of this characteristic.
Return
A Promise to indicate whether the operation is resolved or rejected. The Promise is rejected if there is no Client Characteristic Configuration descriptor (CCCD) for this characteristic.

addDescriptor(DOMString uuid, GattPermissions permissions, ArrayBuffer value)

Description
Adds a descriptor to this characteristic.
Parameter
uuid
UUID of the descriptor to add.
permissions
GattPermissions of the descriptor to add.
value
The initial value of this descriptor.
Return
A Promise to indicate whether the operation is resolved or rejected. If the Promise is resolved, it returns the added BluetoothGattDescriptor object, and property descriptors is also updated with the added descriptor.
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