construct-js

construct-js是一个用于创建字节级数据结构的库。它侧重于声明性API和使用简单性。

安装

npm i construct-js

示例  

以下示例构建一个完全有效的zip存档，其中包含一个文件 - helloworld.txt。

const fs = require('fs');
const {
  RawString,
  U16,
  U32,
  Struct,
} = require('construct-js');

const data = RawString('helloworldhelloworldhelloworldhelloworldhelloworldhelloworldhelloworldhelloworld');
const filename = RawString('helloworld.txt');

const sharedHeaderInfo = Struct('sharedHeaderInfo')
  .field('minVersion', U16(10))
  .field('gpFlag', U16(0))
  .field('compressionMethod', U16(0))
  .field('lastModifiedTime', U16(0))
  .field('lastModifiedDate', U16(0))
  .field('crc32', U32(0))
  .field('compressedSized', U32(data.byteLength))
  .field('uncompressedSized', U32(data.byteLength))
  .field('filenameSize', U16(filename.byteLength))
  .field('extraFieldLength', U16(0));

const localHeader = Struct('localHeader')
  .field('header', U32(0x04034b50))
  .field('sharedHeaderInfo', sharedHeaderInfo)
  .field('filename', filename);

const centralDirectory = Struct('centralDirectory')
  .field('header', U32(0x02014b50))
  .field('madeByVersion', U16(10))
  .field('sharedHeaderInfo', sharedHeaderInfo)
  .field('fileCommentSize', U16(0))
  .field('diskNumber', U16(0))
  .field('internalFileAttributes', U16(0))
  .field('externalFileAttributes', U32(0))
  .field('relativeOffset', U32(0))
  .field('filename', filename);

const endOfCentralDirectory = Struct('endOfCentralDirectory')
  .field('header', U32(0x06054b50))
  .field('diskNumber', U16(0))
  .field('centralDirDiskStart', U16(0))
  .field('numberOfCentralDirsOnDisk', U16(1))
  .field('totalNumberOfCentralDirs', U16(1))
  .field('centralDirSize', U32(0))
  .field('offsetToStart', U32(0))
  .field('commentLength', U16(0));


const zipFile = Struct('ZipFile')
  .field('localHeader', localHeader)
  .field('data', data)
  .field('centralDirectory', centralDirectory)
  .field('endOfCentralDirectory', endOfCentralDirectory);

const offset = zipFile.getOffset('centralDirectory');
endOfCentralDirectory.get('offsetToStart').set(offset);

const fileBuffer = zipFile.toBuffer();

fs.writeFile('./test.zip', fileBuffer, () => {});

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