Gunzip multiple gzip chunks

README.md

Gunzip multiple gzip chunks

https://twitter.com/yteraoka/status/823398592635252736

Test

echo 123 | gzip > a.gz
echo 456 | gzip >> a.gz

npm install stream-stream
cat a.gz | node index.js

cat a.gz | node simple.js

TODO

• Handle magic bytes properly
• Check if stream-stream's implementation is fare enough
• Check more edge cases

index.js

const stream = require('stream');
const zlib = require('zlib');
const ss = require('stream-stream');

// A tranform stream that reads a buffer stream and writes gunzip streams
class MultiGunzip extends stream.Transform {
  constructor() {
    super({ objectMode: true });
  }

  _transform(chunk, encoding, callback) {
    const len = chunk.byteLength;
    let start = 0;
    for (let i = 0; i < len - 1; i += 1) {
      // Magic bytes
      if (chunk[i] === 31 && chunk[i + 1] === 139) {
        if (this.gunzip) {
          this.gunzip.end(chunk.slice(start, i));
        }
        this.gunzip = zlib.createGunzip();
        start = i;
        this.push(this.gunzip);
      }
    }
    // TODO: Check whether the last byte is the first of magic bytes.
    this.gunzip.write(chunk.slice(start));
    callback(null);
  }

  _flush(callback) {
    callback(null);
  }
}

const multi = new MultiGunzip();

process.stdin.pipe(multi).pipe(ss()).pipe(process.stdout);

simple.js

process.stdin.pipe(require('zlib').createGunzip()).pipe(process.stdout);