characteristic.js

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'use strict';

let i = 1;

/**
 * Class that represents a GATT characteristic.
 */
class Characteristic {
    /**
     * Create a characteristic in the Bluetooth `Device's` GATT attribute table.
     *
     * @constructor
     * @param {string} serviceInstanceId The `Service` instanceID this characteristic is to be added to.
     * @param {string} uuid A 128-bit or 16-bit unique identifier for this characteristic.
     * @param {array} value The initial value of this characteristic.
     * @param {Object} properties This GATT characteristic's metadata.
     * @param {Object} options This GATT characteristic's attribute's metadata.
     */
    constructor(serviceInstanceId, uuid, value, properties, options) {
        if (!serviceInstanceId) {
            throw new Error('serviceInstanceId must be provided.');
        }
        if (!value) {
            throw new Error('value must be provided.');
        }
        if (!properties) {
            throw new Error('properties must be provided.');
        }

        // increment global so `characteristicInstanceId` is unique for each created service.
        i += 1;

        this._instanceId = `${serviceInstanceId}.${i}`;
        this._serviceInstanceId = serviceInstanceId;
        this.uuid = uuid;

        if (this.uuid && !(this.uuid.length === 4 || this.uuid.length === 32)) {
            throw new Error('uuid must be 128-bit or 16-bit.');
        }

        this.declarationHandle = null;
        this.valueHandle = null;
        this.value = value;
        this.properties = properties;

        if (options) {
            this.readPerm = options.readPerm;
            this.writePerm = options.writePerm;
            this.variableLength = options.variableLength;
            this.maxLength = options.maxLength;
        }
    }

    /**
     * Get the instanceId of this characteristic (since uuid is not enough to separate between characteristics).
     * @returns {string} Unique ID of this characteristic.
     */
    get instanceId() {
        return this._instanceId;
    }

    /**
     * Get the instance Id of the GATT service that this characteristic belongs to.
     * @returns {string} Unique Id of the service that this characteristic belongs to.
     */
    get serviceInstanceId() {
        return this._serviceInstanceId;
    }

    /**
     * Get the handle of this characteristic in the `Device's` GATT attribute table.
     * @returns {string} The handle of this characteristic in the `Device's` GATT attribute table.
     */
    get handle() {
        return this.valueHandle;
    }
}

module.exports = Characteristic;