characteristic.js

var util = require('util');
var fs  = require('fs');

function conv(num) {
  let b = new ArrayBuffer(4);
  new DataView(b).setUint32(0, num);
  return Array.from(new Uint8Array(b));
}

var bleno = require('bleno');

var BlenoCharacteristic = bleno.Characteristic;

var EchoCharacteristic = function() {
  EchoCharacteristic.super_.call(this, {
    uuid: 'ec0e',
    properties: ['read', 'notify'],
    value: null
  });

  this._value = new Buffer(0);
  this._updateValueCallback = null;
};

util.inherits(EchoCharacteristic, BlenoCharacteristic);

EchoCharacteristic.prototype.onReadRequest = function(offset, callback) {
  console.log('EchoCharacteristic - onReadRequest: value = ' + this._value.toString('hex'));

  let counterValue = parseInt(
        (
          fs.readFileSync("/home/pi/curb-wheel/ram/counter.txt") 
        ).toString()
      );
	
  console.log("value: " +  counterValue)

  callback(this.RESULT_SUCCESS, conv(counterValue));
};

EchoCharacteristic.prototype.onSubscribe = function(maxValueSize, updateValueCallback) {
  console.log('EchoCharacteristic - onSubscribe');

  this._updateValueCallback = updateValueCallback;
};

EchoCharacteristic.prototype.onUnsubscribe = function() {
  console.log('EchoCharacteristic - onUnsubscribe');

  this._updateValueCallback = null;
};

module.exports = EchoCharacteristic;