watch-xdelta/src/util.js

smart-watch xdelta script

/**
 * Created by iyww on 15/9/15.
 */
'use strict';

import co from 'co';
import bfs from 'babel-fs';

/**
 * 生成校验和的低16位
 * @param {Number} 校验和
 * @return {Object.highHex} 校验和高字节
 * @return {Object.lowHex} 校验和低字节
 *
 */
export const checkSumToHex = function(num) {
  let hexStr = num.toString(16);
  let highHex = parseInt(hexStr.slice(-4, -2), 16);
  let lowHex = parseInt(hexStr.slice(-2), 16);
  return {highHex, lowHex};
};

/**
 * 截取文件最后32个字节
 * @param {String} filename 文件名称
 * @return {Object} 返回的对象中包含32字节tail,以及截去tail的新文件名称
 *
 */
export const truncateLast32Bits = co.wrap(function *(filename) {
  let buffer = yield bfs.readFile(filename);
  let tempFile = `${filename}.temp`;
  yield bfs.writeFile(tempFile, buffer.slice(0, -32));
  return {tail: buffer.slice(-32), tempFile};
});