Node.js API详解之 zlib模块用法分析

const zlib = require('zlib');

const gzip = zlib.createGzip();
const fs = require('fs');
const inp = fs.createReadStream('input.txt');
const out = fs.createWriteStream('input.txt.gz');
inp.pipe(gzip).pipe(out);

// 客户端请求示例
const zlib = require('zlib');
const http = require('http');
const fs = require('fs');
const request = http.get({ host: 'example.com',
              path: '/',
              port: 80,
              headers: { 'Accept-Encoding': 'gzip,deflate' } });
request.on('response', (response) => {
 const output = fs.createWriteStream('example.com_index.html');
 switch (response.headers['content-encoding']) {
  // 或者, 只是使用 zlib.createUnzip() 方法去处理这两种情况
  case 'gzip':
   response.pipe(zlib.createGunzip()).pipe(output);
   break;
  case 'deflate':
   response.pipe(zlib.createInflate()).pipe(output);
   break;
  default:
   response.pipe(output);
   break;
 }
});

// 服务端示例
// 对每一个请求运行 gzip 操作的成本是十分高昂的.
// 缓存压缩缓冲区是更加高效的方式.
const zlib = require('zlib');
const http = require('http');
const fs = require('fs');
http.createServer((request, response) => {
 const raw = fs.createReadStream('index.html');
 let acceptEncoding = request.headers['accept-encoding'];
 if (!acceptEncoding) {
  acceptEncoding = '';
 }
 // 注意：这不是一个合适的 accept-encoding 解析器.
 // 查阅 http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3
 if (/\bdeflate\b/.test(acceptEncoding)) {
  response.writeHead(200, { 'Content-Encoding': 'deflate' });
  raw.pipe(zlib.createDeflate()).pipe(response);
 } else if (/\bgzip\b/.test(acceptEncoding)) {
  response.writeHead(200, { 'Content-Encoding': 'gzip' });
  raw.pipe(zlib.createGzip()).pipe(response);
 } else {
  response.writeHead(200, {});
  raw.pipe(response);
 }
}).listen(1337);

const zlib = require('zlib');
// 可接受的 flush 值.
zlib.constants.Z_NO_FLUSH
zlib.constants.Z_PARTIAL_FLUSH
zlib.constants.Z_SYNC_FLUSH
zlib.constants.Z_FULL_FLUSH
zlib.constants.Z_FINISH
zlib.constants.Z_BLOCK
zlib.constants.Z_TREES
// 返回压缩/解压函数的返回值. 发送错误时为负值, 正值用于特殊但正常的事件.
zlib.constants.Z_OK
zlib.constants.Z_STREAM_END
zlib.constants.Z_NEED_DICT
zlib.constants.Z_ERRNO
zlib.constants.Z_STREAM_ERROR
zlib.constants.Z_DATA_ERROR
zlib.constants.Z_MEM_ERROR
zlib.constants.Z_BUF_ERROR
zlib.constants.Z_VERSION_ERROR
// 压缩等级.
zlib.constants.Z_NO_COMPRESSION
zlib.constants.Z_BEST_SPEED
zlib.constants.Z_BEST_COMPRESSION
zlib.constants.Z_DEFAULT_COMPRESSION
// 压缩策略
zlib.constants.Z_FILTERED
zlib.constants.Z_HUFFMAN_ONLY
zlib.constants.Z_RLE
zlib.constants.Z_FIXED
zlib.constants.Z_DEFAULT_STRATEGY

const zlib = require('zlib');
const Options = {
 flush: zlib.constants.Z_NO_FLUSH,
 finishFlush: zlib.constants.Z_FINISH,
 chunkSize: 16*1024,
 windowBits 2, //值在8..15的范围内，这个参数的值越大，内存使用率越高，压缩效果越好。如果使用deflateInit，则默认值为15
 level: 6,  //(压缩级别，值在0-9之间，1速度最快，9压缩比最大，各自折中取值6较为合适。仅压缩有效)
 memLevel: 8,  // (指定多少内存应该内部压缩状态进行分配，1是最小内存速度慢压缩比低。9是最大内存，速度最快。默认值为8。仅压缩有效)
 strategy: 7, // (用于调整压缩算法,仅压缩有效)
 dictionary: ' | | ',  // (仅解压有效，默认值为空字典)
 info: true  //(如果true,返回一个buffer对象和engine)
}

const zlib = require('zlib');
console.log(zlib.constants);
// { Z_NO_FLUSH: 0,
//  Z_PARTIAL_FLUSH: 1,
//  Z_SYNC_FLUSH: 2,
//  Z_FULL_FLUSH: 3,
//  Z_FINISH: 4,
//  Z_BLOCK: 5,
//  Z_OK: 0,
//  Z_STREAM_END: 1,
//  Z_NEED_DICT: 2,
//  Z_ERRNO: -1,
//  Z_STREAM_ERROR: -2,
//  Z_DATA_ERROR: -3,
//  Z_MEM_ERROR: -4,
//  Z_BUF_ERROR: -5,
//  Z_VERSION_ERROR: -6,
//  Z_NO_COMPRESSION: 0,
//  Z_BEST_SPEED: 1,
//  Z_BEST_COMPRESSION: 9,
//  Z_DEFAULT_COMPRESSION: -1,
//  Z_FILTERED: 1,
//  Z_HUFFMAN_ONLY: 2,
//  Z_RLE: 3,
//  Z_FIXED: 4,
//  Z_DEFAULT_STRATEGY: 0,
//  ZLIB_VERNUM: 4784,
//  DEFLATE: 1,
//  INFLATE: 2,
//  GZIP: 3,
//  GUNZIP: 4,
//  DEFLATERAW: 5,
//  INFLATERAW: 6,
//  UNZIP: 7,
//  Z_MIN_WINDOWBITS: 8,
//  Z_MAX_WINDOWBITS: 15,
//  Z_DEFAULT_WINDOWBITS: 15,
//  Z_MIN_CHUNK: 64,
//  Z_MAX_CHUNK: Infinity,
//  Z_DEFAULT_CHUNK: 16384,
//  Z_MIN_MEMLEVEL: 1,
//  Z_MAX_MEMLEVEL: 9,
//  Z_DEFAULT_MEMLEVEL: 8,
//  Z_MIN_LEVEL: -1,
//  Z_MAX_LEVEL: 9,
//  Z_DEFAULT_LEVEL: -1 }

const zlib = require('zlib');
const deflate = zlib.createDeflate();
const fs = require('fs');
const inp = fs.createReadStream('a.js');
console.log( inp.pipe(deflate) );
// Deflate {
//  _readableState:
//  ReadableState { ... },
//  bytesRead: 0,
//  _handle: Zlib { jsref: [Circular], onerror: [Function: zlibOnError] },
//  _hadError: false,
//  _writeState: Uint32Array [ 0, 0 ],
//  _outBuffer: ,
//  _outOffset: 0,
//  _level: -1,
//  _strategy: 0,
//  _chunkSize: 16384,
//  _flushFlag: 0,
//  _scheduledFlushFlag: 0,
//  _origFlushFlag: 0,
//  _finishFlushFlag: 4,
//  _info: undefined }

const zlib = require('zlib');
const deflate = zlib.createDeflate();
const inflate = zlib.createInflate();
const fs = require('fs');
const inp = fs.createReadStream('a.js');
console.log( inp.pipe(deflate).pipe(inflate) );

const zlib = require('zlib');
const deflateRaw = zlib.createDeflateRaw();
const fs = require('fs');
const inp = fs.createReadStream('a.js');
console.log( inp.pipe(deflateRaw) );

const zlib = require('zlib');
const deflateRaw = zlib.createDeflateRaw();
const inflateRaw = zlib.createInflateRaw();
const fs = require('fs');
const inp = fs.createReadStream('a.js');
console.log( inp.pipe(deflateRaw).pipe(inflateRaw) );

const zlib = require('zlib');
const gzip = zlib.createGzip();
const fs = require('fs');
const inp = fs.createReadStream('a.js');
console.log( inp.pipe(gzip) );

const zlib = require('zlib');
const gzip = zlib.createGzip();
const gunzip = zlib.createGunzip();
const fs = require('fs');
const inp = fs.createReadStream('a.js');
console.log( inp.pipe(gzip).pipe(gunzip) );

const zlib = require('zlib');
const gzip = zlib.createGzip();
const unzip = zlib.createUnzip();
const fs = require('fs');
const inp = fs.createReadStream('a.js');
console.log( inp.pipe(gzip).pipe(unzip) );

const input = '.................................';
zlib.deflate(input, (err, buffer) => {
 if (!err) {
  console.log(buffer.toString('base64'));
 } else {
  // 错误处理
 }
});
const buffer = Buffer.from('eJzT0yMAAGTvBe8=', 'base64');
zlib.unzip(buffer, (err, buffer) => {
 if (!err) {
  console.log(buffer.toString());
 } else {
  // 错误处理
 }
});