# Zlib

> Stability: 2 - Stable

Compressing or decompressing a stream (such as a file) can be accomplished by

piping the source stream data through a `zlib` stream into a destination stream:

It is also possible to compress or decompress data in a single step:

zlib.deflate(input, (err, buffer) => {

const buffer = Buffer.from('eJzT0yMAAGTvBe8=', 'base64');

zlib.unzip(buffer, (err, buffer) => {

content-encoding mechanisms defined by

message.

ought to be cached. See [Memory Usage Tuning][] for more information

on the speed/memory/compression tradeoffs involved in `zlib` usage.

const request = http.get({ host: 'example.com',

request.on('response', (response) => {

const output = fs.createWriteStream('example.com_index.html');

```

```js

// Note: This is not a conformant accept-encoding parser.

response.writeHead(200, { 'Content-Encoding': 'deflate' });

response.writeHead(200, { 'Content-Encoding': 'gzip' });

By default, the `zlib` methods will throw an error when decompressing

const buffer = Buffer.from('eJzT0yMA', 'base64');

From `zlib/zconf.h`, modified to node.js's usage:

<!-- eslint-disable semi -->

```js

(1 << (windowBits + 2)) + (1 << (memLevel + 9))

```

That is: 128K for windowBits=15 + 128K for memLevel = 8

For example, to reduce the default memory requirements from 256K to 128K, the

options should be set to:

```js

const options = { windowBits: 14, memLevel: 7 };

```

This will, however, generally degrade compression.

The memory requirements for inflate are (in bytes) `1 << windowBits`.

That is, 32K for windowBits=15 (default value) plus a few kilobytes

The speed of `zlib` compression is affected most dramatically by the

speed, at the cost of memory usage.

Calling [`.flush()`][] on a compression stream will make `zlib` return as much

## Constants

*Note*: Previously, the constants were available directly from

changes:

- version: v8.0.0

-->

Each class takes an `options` object. All options are optional.

* `dictionary` {Buffer|TypedArray|DataView} (deflate/inflate only, empty dictionary by

default)

Compress data using deflate, and do not append a `zlib` header.

-->

-->

-->

`kind` defaults to `zlib.constants.Z_FULL_FLUSH`.

Calling this only flushes data from the internal `zlib` state, and does not

### zlib.params(level, strategy, callback)

## zlib.constants

Provides an object enumerating Zlib-related constants.

## zlib.createDeflate([options])

Returns a new [Deflate][] object with an [options][].

Returns a new [DeflateRaw][] object with an [options][].

*Note*: The zlib library rejects requests for 256-byte windows (i.e.,

## zlib.createGunzip([options])

Returns a new [Gunzip][] object with an [options][].

Returns a new [Gzip][] object with an [options][].

Returns a new [Inflate][] object with an [options][].

Returns a new [InflateRaw][] object with an [options][].

Returns a new [Unzip][] object with an [options][].