advlib-ble-manufacturers/lib/utils.js

Wireless advertising packet decoding library for Bluetooth Low Energy manufacturer-specific data. We believe in an open Internet of Things.

/**
 * Copyright reelyActive 2015-2020
 * We believe in an open Internet of Things
 */


const SIGNATURE_SEPARATOR = '/';


/**
 * Convert the given hexadecimal string or Buffer to a Buffer.
 * @param {Object} data A hexadecimal-string or Buffer.
 * @return {Object} The data as a Buffer, or null if invalid data format.
 */
function convertToBuffer(data) {
  if(Buffer.isBuffer(data)) {
    return data;
  }

  if(typeof data === 'string') {
    data = data.toLowerCase();
    let isHex = /[0-9a-f]+/.test(data);
    if(isHex) {
      return Buffer.from(data, 'hex');
    }
  }

  return null;
}


/**
 * Convert the given data to a hexadecimal string of the given number of bytes.
 * @param {Object} data The data to convert (Number, String or Buffer).
 * @param {Number} length The target length of the string in bytes.
 * @param {boolean} reverseEndianness Optionally reverse the endianness.
 * @return {String} The data as a hexadecimal string.
 */
function convertToHexString(data, length, reverseEndianness) {
  let hexString = null;

  if(Number.isInteger(data) && (data >= 0)) {
    hexString = data.toString(16).padStart(length * 2, '0');
  }
  if(Buffer.isBuffer(data)) {
    hexString = data.toString('hex').padStart(length * 2, '0');
  }
  if(typeof data === 'string') {
    hexString = data.padStart(length * 2, '0');
  }

  if(hexString && (reverseEndianness === true)) {
    return hexString.match(/.{2}/g).reverse().join('');
  }

  return hexString;
}


/**
 * Convert the given signed 8.8 Buffer to a floating point Number.
 * @param {Object} data The signed 8.8 Bufferdata to convert.
 * @return {Number} The floating point representation as a Number.
 */
function parseSigned88(data) {
  return data.readInt8() + (data.readUInt8(1) / 256);
}


/**
 * Convert a ZigZag-encoded integer to a signed integer.
 * @param {Number} data The ZigZag-encoded integer.
 * @return {Number} The decoded signed integer.
 */
function decodeZigZag(data) {
  return (data >> 1) ^ -(data & 1);
}


module.exports.SIGNATURE_SEPARATOR = SIGNATURE_SEPARATOR;
module.exports.convertToBuffer = convertToBuffer;
module.exports.convertToHexString = convertToHexString;
module.exports.parseSigned88 = parseSigned88;
module.exports.decodeZigZag = decodeZigZag;