Stuck on an issue?

I am seeing a few issues with Gzip/Gunzip on Deno.

One is, compressing then decompressing modest size text files, give corrupt and much smaller uncompressed version. Another is compressing a modest sized binary file is generating an invalid compressed file format, and when attempting to decompress get an Invalid gzip data exception.

I wrote the following test to demonstrate the problem:

import * as fflate from 'https://cdn.skypack.dev/fflate';

async function zpipe(reader: Deno.Reader, stream: any) {
  let total = 0;
  async function push(p: Uint8Array, isLast?: boolean) {
    console.log('push', p.byteLength);
    debugger;
    await stream.push(p, isLast);
    total += p.byteLength;
  }
  let prevBlock;
  for await (const block of Deno.iter(reader)) {
    if (prevBlock) await push(prevBlock);
    prevBlock = block;
  }
  if (prevBlock) await push(prevBlock, true);
  console.log(`pushed ${total} bytes`);
}

function zip(from: string, to: string, options = {}) {
  let total = 0;
  return new Promise<void>(async (resolve, reject) => {
    const hFrom = await Deno.open(from, { read: true });
    const hTo = await Deno.open(to, { write: true, create: true, truncate: true });
    const zipper: any = new fflate.Gzip({ level: 9 }, async (chunk: Uint8Array, isLast: boolean) => {
      console.log('zip write chunk', chunk.byteLength);
      await hTo.write(chunk);
      total += chunk.byteLength;
      if (isLast) {
        console.log(`zip close dest file, ${total} bytes`);
        hTo.close();
        resolve();
      }
    });
    await zpipe(hFrom, zipper);
    console.log('zip close source file');
    hFrom.close();
  });
}

function unzip(from: string, to: string) {
  let total = 0;
  return new Promise<void>(async (resolve, reject) => {
    const hFrom = await Deno.open(from, { read: true });
    const hTo = await Deno.open(to, { write: true, create: true, truncate: true });
    const unzipper: any = new fflate.Gunzip();
    unzipper.ondata = async (chunk: Uint8Array, isLast: boolean) => {
      console.log('unzip write chunk', chunk.byteLength);
      await hTo.write(chunk);
      total += chunk.length;
      if (isLast) {
        console.log(`unzip close dest file, ${total} bytes`);
        hTo.close();
        resolve();
      }
    };
    await zpipe(hFrom, unzipper);
    console.log('unzip close source file');
    hFrom.close();
  });
}

const fn = Deno.args[0];
await zip(fn, `${fn}.gz`);
await unzip(`${fn}.gz`, `${fn}.unzipped`);

As a test, I downloaded fflate.js and compressed and decompressed that using the code above:

deno run --allow-all gzip.ts fflate.js

The resulting file sizes are:

-a----       20/03/2021     15:43          54748 fflate.js
-a----       21/03/2021     00:57          14322 fflate.js.gz
-a----       21/03/2021     00:57          16384 fflate.js.unzipped

For the binary file test, I generated a 32kb binary random file using dd

dd if=/dev/random of=LARGE_FILE ibs=1k count=32

Then compress it with the above code:

deno run --allow-all gzip.ts LARGE_FILE

This throws an error on the unzip:

error: Uncaught (in promise) invalid gzip data

And file reports a strange size on the compressed file:

LARGE_DATA.gz:        gzip compressed data, last modified: Sun Mar 21 01:01:11 2021, max compression, from Unix, original size modulo 2^32 100822718