Support "deflate-raw" format

[ricea]

For applications such as reading/writing zip files it's necessary to have access to the raw deflate stream without any headers or footers. We should add a "deflate-raw" format to support this.

See previous discussion at https://github.com/ricea/compressstream-explainer/issues/8.

[taralx]

Note that zip files can be decompressed (and checksummed!) using gzip:

const GZIP_HEADER = Uint8Array.from([
  31, 139, // gzip magic
  8, // deflate
  0, // no extra fields
  0, 0, 0, 0, // mtime (n/a)
  0, 0, // extra flags, OS
]);

function decompressZip(stream, crc, uncompressedSize) {
  return stream.pipeThrough(new TransformStream({
    start(controller) {
      controller.enqueue(GZIP_HEADER);
    },
    flush(controller) {
      const tmp = new DataView(new ArrayBuffer(8));
      tmp.setUint32(0, crc, true);
      tmp.setUint32(4, uncompressedSize, true);
      controller.enqueue(new Uint8Array(tmp.buffer));
    }
  })).pipeThrough(new DecompressionStream('gzip'));
}

[taralx]

Note that for the creation side, you need CRC, so you may as well use gzip there too.

[ricea]

@taralx That's impressive, but I'd prefer it if people didn't have to put together a fake gzip wrapper just to decode a zip file.

I like the CRC trick. It doesn't look like there'd be an easy way to get the same functionality with "deflate-raw".

[taralx]

In decompression it can be a constructor option. In compression though, I'm not sure either.

[panva]

I am likewise looking for support of 'inflate-raw' and 'deflate-raw' formats.

[nikhil1511]

We are also interested in having support for "deflate-raw" as it is required for zipping. With "gzip" or "deflate" formats, additional workarounds would be required which is not very neat. So, it would be super helpful if raw compression format can be supported. Thanks!

[yutakahirano]

Chrome is interested in this feature, and wants to add this feature. Are there any opinions from other browser vendors?

[yutakahirano]

Working at #43. Any feedbacks will be appreciated.

[yutakahirano]

@ricea I cannot close this, but I think this can be closed now.

[ricea]

Done.