unwxvpkg/index.js

unpack wx[av]pkg

'use strict';

const _ = require('./src/util');

const DEFAULT = {
  firstMark: [0xbe],
  lastMark: [0xed],
};

function wxapkgFileInfo() {
  this.nameLen = 0;
  this.name = '';
  this.offset = 0;
  this.size = 0;
}

class Wxapkg {
  constructor(file) {
    this.index = 0; // 解码游标
    this.buffer = new Uint8Array(file);
  }

  /**
   * 读取buffer数组的指定字节数
   * @param  {Number} length 读取长度
   * @return {Array}         读取到的数据
   */
  readBytes(length) {
    let buffer = _.readBytes(this.buffer, this.index, length);
    this.index += length;

    return buffer;
  }

  /**
   * 解码
   * @return {Array}        文件数组
   */
  _decode() {
    if (!this.buffer) {
      throw new Error('不存在待解码数据！');
    }
    this._decodeHeader(); // 解析头部信息
    return this._decodeChunkInfo(); // 解析数据块元数据
  }

  /**
   * 解码输出文件
   * @return {Void}
   */
  decode() {
    let files = [];
    let fileInfoList = this._decode();
    fileInfoList.forEach((f) => {
      let file = {};
      file.chunk = _.readBytes(this.buffer, f.offset, f.size);
      file.name = f.name;
      files.push(file);
    });
    return files;
  }

  /**
   * 解码头部信息
   * @return {Void}
   */
  _decodeHeader() {
    if (this.index !== 0) {
      throw new Error('index属性指向非0！');
    }

    this.firstMark = this.readBytes(1);
    if (!_.equal(this.firstMark, DEFAULT.firstMark)) {
      throw new Error('wxpakg文件错误 - firstMark');
    }

    this.fileInfo = _.readInt32(this.readBytes(4));

    this.indexInfoLength = _.readInt32(this.readBytes(4));

    this.bodyInfoLength = _.readInt32(this.readBytes(4));

    this.lastMark = this.readBytes(1);

    if (!_.equal(this.lastMark, DEFAULT.lastMark)) {
      throw new Error('wxpakg文件错误 - lastMark');
    }

    this.fileCount = _.readInt32(this.readBytes(4));

    console.log(`fileCount = ${this.fileCount}`);
  }

  /**
   * 解析元数据
   * @return {Array} 数据块元数据数组
   */
  _decodeChunkInfo() {
    let fileList = [];
    for (let i = 0; i < this.fileCount; i++) {
      let fileInfo = new wxapkgFileInfo();
      fileInfo.nameLen = _.readInt32(this.readBytes(4));
      fileInfo.name = _.bufferToString(this.readBytes(fileInfo.nameLen));
      fileInfo.offset = _.readInt32(this.readBytes(4));
      fileInfo.size = _.readInt32(this.readBytes(4));

      console.log(`fileName - ${fileInfo.name}`);

      fileList.push(fileInfo);
    }
    return fileList;
  }
}

module.exports = Wxapkg;