Node.js v25.9.0 documentation

Iterable Compression#

The node:zlib/iter module provides compression and decompression transforms for use with the node:stream/iter iterable streams API.

This module is available only when the --experimental-stream-iter CLI flag is enabled.

Each algorithm has both an async variant (stateful async generator, for use with pull() and pipeTo()) and a sync variant (stateful sync generator, for use with pullSync() and pipeToSync()).

The async transforms run compression on the libuv threadpool, overlapping I/O with JavaScript execution. The sync transforms run compression directly on the main thread.

Note: The defaults for these transforms are tuned for streaming throughput, and differ from the defaults in node:zlib. In particular, gzip/deflate default to level 4 (not 6) and memLevel 9 (not 8), and Brotli defaults to quality 6 (not 11). These choices match common HTTP server configurations and provide significantly faster compression with only a small reduction in compression ratio. All defaults can be overridden via options.

import { from, pull, bytes, text } from 'node:stream/iter';
import { compressGzip, decompressGzip } from 'node:zlib/iter';

// Async round-trip
const compressed = await bytes(pull(from('hello'), compressGzip()));
const original = await text(pull(from(compressed), decompressGzip()));
console.log(original); // 'hello'
const { from, pull, bytes, text } = require('node:stream/iter');
const { compressGzip, decompressGzip } = require('node:zlib/iter');

async function run() {
  const compressed = await bytes(pull(from('hello'), compressGzip()));
  const original = await text(pull(from(compressed), decompressGzip()));
  console.log(original); // 'hello'
}

run().catch(console.error);
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import { fromSync, pullSync, textSync } from 'node:stream/iter';
import { compressGzipSync, decompressGzipSync } from 'node:zlib/iter';

// Sync round-trip
const compressed = pullSync(fromSync('hello'), compressGzipSync());
const original = textSync(pullSync(compressed, decompressGzipSync()));
console.log(original); // 'hello'
const { fromSync, pullSync, textSync } = require('node:stream/iter');
const { compressGzipSync, decompressGzipSync } = require('node:zlib/iter');

const compressed = pullSync(fromSync('hello'), compressGzipSync());
const original = textSync(pullSync(compressed, decompressGzipSync()));
console.log(original); // 'hello'
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compressBrotli([options])#

compressBrotliSync([options])#

• options <Object>
  • chunkSize <number> Output buffer size. Default: 65536 (64 KB).
  • params <Object> Key-value object where keys and values are zlib.constants entries. The most important compressor parameters are:
    • BROTLI_PARAM_MODE -- BROTLI_MODE_GENERIC (default), BROTLI_MODE_TEXT, or BROTLI_MODE_FONT.
    • BROTLI_PARAM_QUALITY -- ranges from BROTLI_MIN_QUALITY to BROTLI_MAX_QUALITY. Default: 6 (not BROTLI_DEFAULT_QUALITY which is 11). Quality 6 is appropriate for streaming; quality 11 is intended for offline/build-time compression.
    • BROTLI_PARAM_SIZE_HINT -- expected input size. Default: 0 (unknown).
    • BROTLI_PARAM_LGWIN -- window size (log2). Default: 20 (1 MB). The Brotli library default is 22 (4 MB); the reduced default saves memory without significant compression impact for streaming workloads.
    • BROTLI_PARAM_LGBLOCK -- input block size (log2). See the Brotli compressor options in the zlib documentation for the full list.
  • dictionary <Buffer> | <TypedArray> | <DataView>
• Returns: <Object> A stateful transform.

Create a Brotli compression transform. Output is compatible with zlib.brotliDecompress() and decompressBrotli()/decompressBrotliSync().

compressDeflate([options])#

compressDeflateSync([options])#

• options <Object>
  • chunkSize <number> Output buffer size. Default: 65536 (64 KB).
  • level <number> Compression level (0-9). Default: 4.
  • windowBits <number> Default: Z_DEFAULT_WINDOWBITS (15).
  • memLevel <number> Default: 9.
  • strategy <number> Default: Z_DEFAULT_STRATEGY.
  • dictionary <Buffer> | <TypedArray> | <DataView>
• Returns: <Object> A stateful transform.

Create a deflate compression transform. Output is compatible with zlib.inflate() and decompressDeflate()/decompressDeflateSync().

compressGzip([options])#

compressGzipSync([options])#

• options <Object>
  • chunkSize <number> Output buffer size. Default: 65536 (64 KB).
  • level <number> Compression level (0-9). Default: 4.
  • windowBits <number> Default: Z_DEFAULT_WINDOWBITS (15).
  • memLevel <number> Default: 9.
  • strategy <number> Default: Z_DEFAULT_STRATEGY.
  • dictionary <Buffer> | <TypedArray> | <DataView>
• Returns: <Object> A stateful transform.

Create a gzip compression transform. Output is compatible with zlib.gunzip() and decompressGzip()/decompressGzipSync().

compressZstd([options])#

compressZstdSync([options])#

• options <Object>
  • chunkSize <number> Output buffer size. Default: 65536 (64 KB).
  • params <Object> Key-value object where keys and values are zlib.constants entries. The most important compressor parameters are:
    • ZSTD_c_compressionLevel -- Default: ZSTD_CLEVEL_DEFAULT (3).
    • ZSTD_c_checksumFlag -- generate a checksum. Default: 0.
    • ZSTD_c_strategy -- compression strategy. Values include ZSTD_fast, ZSTD_dfast, ZSTD_greedy, ZSTD_lazy, ZSTD_lazy2, ZSTD_btlazy2, ZSTD_btopt, ZSTD_btultra, ZSTD_btultra2. See the Zstd compressor options in the zlib documentation for the full list.
  • pledgedSrcSize <number> Expected uncompressed size (optional hint).
  • dictionary <Buffer> | <TypedArray> | <DataView>
• Returns: <Object> A stateful transform.

Create a Zstandard compression transform. Output is compatible with zlib.zstdDecompress() and decompressZstd()/decompressZstdSync().

decompressBrotli([options])#

decompressBrotliSync([options])#

• options <Object>
  • chunkSize <number> Output buffer size. Default: 65536 (64 KB).
  • params <Object> Key-value object where keys and values are zlib.constants entries. Available decompressor parameters:
    • BROTLI_DECODER_PARAM_DISABLE_RING_BUFFER_REALLOCATION -- boolean flag affecting internal memory allocation.
    • BROTLI_DECODER_PARAM_LARGE_WINDOW -- boolean flag enabling "Large Window Brotli" mode (not compatible with RFC 7932). See the Brotli decompressor options in the zlib documentation for details.
  • dictionary <Buffer> | <TypedArray> | <DataView>
• Returns: <Object> A stateful transform.

Create a Brotli decompression transform.

decompressDeflate([options])#

decompressDeflateSync([options])#

• options <Object>
  • chunkSize <number> Output buffer size. Default: 65536 (64 KB).
  • windowBits <number> Default: Z_DEFAULT_WINDOWBITS (15).
  • dictionary <Buffer> | <TypedArray> | <DataView>
• Returns: <Object> A stateful transform.

Create a deflate decompression transform.

decompressGzip([options])#

decompressGzipSync([options])#

• options <Object>
  • chunkSize <number> Output buffer size. Default: 65536 (64 KB).
  • windowBits <number> Default: Z_DEFAULT_WINDOWBITS (15).
  • dictionary <Buffer> | <TypedArray> | <DataView>
• Returns: <Object> A stateful transform.

Create a gzip decompression transform.

decompressZstd([options])#

decompressZstdSync([options])#

• options <Object>
  • chunkSize <number> Output buffer size. Default: 65536 (64 KB).
  • params <Object> Key-value object where keys and values are zlib.constants entries. Available decompressor parameters:
    • ZSTD_d_windowLogMax -- maximum window size (log2) the decompressor will allocate. Limits memory usage against malicious input. See the Zstd decompressor options in the zlib documentation for details.
  • dictionary <Buffer> | <TypedArray> | <DataView>
• Returns: <Object> A stateful transform.

Create a Zstandard decompression transform.