Compression API

The WHATWG CompressionStream / DecompressionStream interfaces, backed by a native miniz extension. CompressionStream compresses a stream of chunks; DecompressionStream reverses the operation.

Globals

Global	Type	Description
CompressionStream	class	Transform stream that compresses written chunks.
DecompressionStream	class	Transform stream that decompresses written chunks.

Both are standard Streams — they expose .readable and .writable and can be piped through a pipeline.

new CompressionStream(format)

Creates a compression transform. format defaults to 'gzip'.

Format	Wire format
'gzip'	gzip wrapper (10-byte header + DEFLATE + CRC32 + ISIZE)
'deflate'	zlib wrapper (2-byte header + DEFLATE + Adler-32 trailer)
'deflate-raw'	raw DEFLATE, no wrapper

let cs = new CompressionStream('gzip');
let rs = new ReadableStream({ start(c) { c.enqueue(new TextEncoder().encode('hello world')); c.close(); } });
let chunks = [];

await rs
  .pipeThrough(cs)
  .pipeTo(new WritableStream({ write(c) { chunks.push(c); } }));

let gzipBytes = chunks[0]; // Uint8Array of gzip-compressed data

new DecompressionStream(format)

Creates a decompression transform. format defaults to 'gzip' and must match the wrapper used to produce the data ('gzip', 'deflate', or 'deflate-raw').

let ds = new DecompressionStream('gzip');
let rs = new ReadableStream({ start(c) { c.enqueue(gzipBytes); c.close(); } });
let out = [];

await rs
  .pipeThrough(ds)
  .pipeTo(new WritableStream({ write(c) { out.push(c); } }));

let text = new TextDecoder().decode(out[0]); // "hello world"

An unsupported format name throws Error: CompressionStream: unsupported format: <fmt> (or DecompressionStream:).

Piping with HTTP

A typical use is compressing a fetch response body:

let res = await fetch('https://example.com/big.json');
let decompressed = res.body.pipeThrough(new DecompressionStream('gzip'));
let text = await new Response(decompressed).text();

Build option

Compression requires QZ_WITH_COMPRESS=ON (default) at build time. When disabled, the classes exist but error the readable side with TypeError: Native compression extension not available. See Build Options.

Notes

• Input chunks should be Uint8Array or ArrayBuffer (other chunk types are coerced via new Uint8Array(...)).
• All-at-once processing: the full input is held in memory until the stream closes, so extremely large streams are not memory-bounded.
• Decompression of malformed, truncated, or empty DEFLATE input errors the readable side (with a bounded iteration cap) rather than producing partial output or hanging forever.