Zlib | Node.js v26.8.0 Documentation

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Table of contents

- Zlib
  - Threadpool usage and performance considerations
  - Compressing HTTP requests and responses
  - Memory usage tuning
    - For zlib-based streams
    - For Brotli-based streams
    - For Zstd-based streams
  - Flushing
  - Constants
    - zlib constants
    - Brotli constants
      - Flush operations
      - Compressor options
      - Decompressor options
    - Zstd constants
      - Flush operations
      - Compressor options
      - Strategy options
      - Pledged Source Size
      - Decompressor options
  - Class: `Options`
  - Class: `BrotliOptions`
  - Class: `zlib.BrotliCompress`
  - Class: `zlib.BrotliDecompress`
  - Class: `zlib.Deflate`
  - Class: `zlib.DeflateRaw`
  - Class: `zlib.Gunzip`
  - Class: `zlib.Gzip`
  - Class: `zlib.Inflate`
  - Class: `zlib.InflateRaw`
  - Class: `zlib.Unzip`
  - Class: `zlib.ZipBuffer`
    - `new zlib.ZipBuffer(buffer)`
    - `zipBuffer.add(filename, data[, options])`
    - `zipBuffer.addSync(filename, data[, options])`
    - `zipBuffer.addEntry(entry)`
    - `zipBuffer.clear()`
    - `zipBuffer.comment`
    - `zipBuffer.delete(name)`
    - `zipBuffer.entries()`
    - `zipBuffer.forEach(callback[, thisArg])`
    - `zipBuffer.get(name)`
    - `zipBuffer.has(name)`
    - `zipBuffer.keys()`
    - `zipBuffer.size`
    - `zipBuffer.toBuffer([options])`
    - `zipBuffer.toBufferSync([options])`
    - `zipBuffer.values()`
    - `zipBuffer.writable`
  - Class: `zlib.ZipEntry`
    - Static method: `zlib.ZipEntry.create(filename, data[, options])`
    - Static method: `zlib.ZipEntry.createStream(filename, source[, options])`
    - Static method: `zlib.ZipEntry.createSymlink(filename, target[, options])`
    - Static method: `zlib.ZipEntry.createSync(filename, data[, options])`
    - Static method: `zlib.ZipEntry.read(buffer)`
    - `zipEntry.comment`
    - `zipEntry.compressed`
    - `zipEntry.compressedSize`
    - `zipEntry.content([options])`
    - `zipEntry.contentSync([options])`
    - `zipEntry.contentIterator([options])`
    - `zipEntry.crc32`
    - `zipEntry.flags`
    - `zipEntry.isDirectory`
    - `zipEntry.isFile`
    - `zipEntry.isSymlink`
    - `zipEntry.mode`
    - `zipEntry.modified`
    - `zipEntry.method`
    - `zipEntry.name`
    - `zipEntry.nameBuffer`
    - `zipEntry.rawContent`
    - `zipEntry.size`
  - Class: `zlib.ZipFile`
    - Static method: `zlib.ZipFile.open(filename[, options])`
    - Static method: `zlib.ZipFile.openSync(filename[, options])`
    - `zipFile.add(filename, data[, options])`
    - `zipFile.addEntry(entry)`
    - `zipFile.addEntrySync(entry)`
    - `zipFile.addSync(filename, data[, options])`
    - `zipFile.close()`
    - `zipFile.closeSync()`
    - `zipFile.comment`
    - `zipFile.compact([comment])`
    - `zipFile.compactSync([comment])`
    - `zipFile.delete(name)`
    - `zipFile.deleteSync(name)`
    - `zipFile.entries()`
    - `zipFile.entriesSync()`
    - `zipFile.forEach(callback[, thisArg])`
    - `zipFile.forEachSync(callback[, thisArg])`
    - `zipFile.get(name)`
    - `zipFile.getSync(name)`
    - `zipFile.has(name)`
    - `zipFile.keys()`
    - `zipFile.size`
    - `zipFile.stream(name[, options])`
    - `zipFile.values()`
    - `zipFile.valuesSync()`
    - `zipFile.writable`
  - Class: `zlib.ZlibBase`
    - `zlib.bytesWritten`
    - `zlib.close([callback])`
    - `zlib.flush([kind, ]callback)`
    - `zlib.params(level, strategy, callback)`
    - `zlib.reset()`
  - Class: `ZstdOptions`
  - Class: `zlib.ZstdCompress`
  - Class: `zlib.ZstdDecompress`
  - `zlib.constants`
  - `zlib.crc32(data[, value])`
  - `zlib.createBrotliCompress([options])`
  - `zlib.createBrotliDecompress([options])`
  - `zlib.createDeflate([options])`
  - `zlib.createDeflateRaw([options])`
  - `zlib.createGunzip([options])`
  - `zlib.createGzip([options])`
  - `zlib.createInflate([options])`
  - `zlib.createInflateRaw([options])`
  - `zlib.createUnzip([options])`
  - `zlib.createZipArchive(entries[, options])`
  - `zlib.createZipArchiveSync(entries[, options])`
  - `zlib.zipFiles(files[, options])`
  - `zlib.createZstdCompress([options])`
  - `zlib.createZstdDecompress([options])`
  - `zlib.getMaxZipContentSize()`
  - `zlib.setMaxZipContentSize(size)`
  - Convenience methods
    - `zlib.brotliCompress(buffer[, options], callback)`
    - `zlib.brotliCompressSync(buffer[, options])`
    - `zlib.brotliDecompress(buffer[, options], callback)`
    - `zlib.brotliDecompressSync(buffer[, options])`
    - `zlib.deflate(buffer[, options], callback)`
    - `zlib.deflateSync(buffer[, options])`
    - `zlib.deflateRaw(buffer[, options], callback)`
    - `zlib.deflateRawSync(buffer[, options])`
    - `zlib.gunzip(buffer[, options], callback)`
    - `zlib.gunzipSync(buffer[, options])`
    - `zlib.gzip(buffer[, options], callback)`
    - `zlib.gzipSync(buffer[, options])`
    - `zlib.inflate(buffer[, options], callback)`
    - `zlib.inflateSync(buffer[, options])`
    - `zlib.inflateRaw(buffer[, options], callback)`
    - `zlib.inflateRawSync(buffer[, options])`
    - `zlib.unzip(buffer[, options], callback)`
    - `zlib.unzipSync(buffer[, options])`
    - `zlib.zstdCompress(buffer[, options], callback)`
    - `zlib.zstdCompressSync(buffer[, options])`
    - `zlib.zstdDecompress(buffer[, options], callback)`
    - `zlib.zstdDecompressSync(buffer[, options])`
  - Iterable Compression
    - `compressBrotli([options])`
    - `compressBrotliSync([options])`
    - `compressDeflate([options])`
    - `compressDeflateSync([options])`
    - `compressGzip([options])`
    - `compressGzipSync([options])`
    - `compressZstd([options])`
    - `compressZstdSync([options])`
    - `decompressBrotli([options])`
    - `decompressBrotliSync([options])`
    - `decompressDeflate([options])`
    - `decompressDeflateSync([options])`
    - `decompressGzip([options])`
    - `decompressGzipSync([options])`
    - `decompressZstd([options])`
    - `decompressZstdSync([options])`

## Zlib#

Source Code: lib/zlib.js

Stability: 2 - Stable

The `node:zlib` module provides compression functionality implemented using Gzip, Deflate/Inflate, Brotli, and Zstd.

To access it:

    import zlib from 'node:zlib';
    const zlib = require('node:zlib');
    javascript

Compression and decompression are built around the Node.js Streams API.

Compressing or decompressing a stream (such as a file) can be accomplished by piping the source stream through a `zlib` `Transform` stream into a destination stream:

    import {
      createReadStream,
      createWriteStream,
    } from 'node:fs';
    import process from 'node:process';
    import { createGzip } from 'node:zlib';
    import { pipeline } from 'node:stream';

    const gzip = createGzip();
    const source = createReadStream('input.txt');
    const destination = createWriteStream('input.txt.gz');

    pipeline(source, gzip, destination, (err) => {
      if (err) {
        console.error('An error occurred:', err);
        process.exitCode = 1;
      }
    });
    const {
      createReadStream,
      createWriteStream,
    } = require('node:fs');
    const { createGzip } = require('node:zlib');
    const { pipeline } = require('node:stream');

    const gzip = createGzip();
    const source = createReadStream('input.txt');
    const destination = createWriteStream('input.txt.gz');

    pipeline(source, gzip, destination, (err) => {
      if (err) {
        console.error('An error occurred:', err);
        process.exitCode = 1;
      }
    });
    javascript

Or, using the promise `pipeline` API:

    import {
      createReadStream,
      createWriteStream,
    } from 'node:fs';
    import { createGzip } from 'node:zlib';
    import { pipeline } from 'node:stream/promises';

    async function do_gzip(input, output) {
      const gzip = createGzip();
      const source = createReadStream(input);
      const destination = createWriteStream(output);
      await pipeline(source, gzip, destination);
    }

    await do_gzip('input.txt', 'input.txt.gz');
    const {
      createReadStream,
      createWriteStream,
    } = require('node:fs');
    const { createGzip } = require('node:zlib');
    const { pipeline } = require('node:stream/promises');

    async function do_gzip(input, output) {
      const gzip = createGzip();
      const source = createReadStream(input);
      const destination = createWriteStream(output);
      await pipeline(source, gzip, destination);
    }

    do_gzip('input.txt', 'input.txt.gz')
      .catch((err) => {
        console.error('An error occurred:', err);
        process.exitCode = 1;
      });
    javascript

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

    import process from 'node:process';
    import { Buffer } from 'node:buffer';
    import { deflate, unzip } from 'node:zlib';

    const input = '.................................';
    deflate(input, (err, buffer) => {
      if (err) {
        console.error('An error occurred:', err);
        process.exitCode = 1;
      }
      console.log(buffer.toString('base64'));
    });

    const buffer = Buffer.from('eJzT0yMAAGTvBe8=', 'base64');
    unzip(buffer, (err, buffer) => {
      if (err) {
        console.error('An error occurred:', err);
        process.exitCode = 1;
      }
      console.log(buffer.toString());
    });

    // Or, Promisified

    import { promisify } from 'node:util';
    const do_unzip = promisify(unzip);

    const unzippedBuffer = await do_unzip(buffer);
    console.log(unzippedBuffer.toString());
    const { deflate, unzip } = require('node:zlib');

    const input = '.................................';
    deflate(input, (err, buffer) => {
      if (err) {
        console.error('An error occurred:', err);
        process.exitCode = 1;
      }
      console.log(buffer.toString('base64'));
    });

    const buffer = Buffer.from('eJzT0yMAAGTvBe8=', 'base64');
    unzip(buffer, (err, buffer) => {
      if (err) {
        console.error('An error occurred:', err);
        process.exitCode = 1;
      }
      console.log(buffer.toString());
    });

    // Or, Promisified

    const { promisify } = require('node:util');
    const do_unzip = promisify(unzip);

    do_unzip(buffer)
      .then((buf) => console.log(buf.toString()))
      .catch((err) => {
        console.error('An error occurred:', err);
        process.exitCode = 1;
      });
    javascript

### Threadpool usage and performance considerations#

All `zlib` APIs, except those that are explicitly synchronous, use the Node.js internal threadpool. This can lead to surprising effects and performance limitations in some applications.

Creating and using a large number of zlib objects simultaneously can cause significant memory fragmentation.

    import zlib from 'node:zlib';
    import { Buffer } from 'node:buffer';

    const payload = Buffer.from('This is some data');

    // WARNING: DO NOT DO THIS!
    for (let i = 0; i < 30000; ++i) {
      zlib.deflate(payload, (err, buffer) => {});
    }
    const zlib = require('node:zlib');

    const payload = Buffer.from('This is some data');

    // WARNING: DO NOT DO THIS!
    for (let i = 0; i < 30000; ++i) {
      zlib.deflate(payload, (err, buffer) => {});
    }
    javascript

In the preceding example, 30,000 deflate instances are created concurrently. Because of how some operating systems handle memory allocation and deallocation, this may lead to significant memory fragmentation.

It is strongly recommended that the results of compression operations be cached to avoid duplication of effort.

### Compressing HTTP requests and responses#

The `node:zlib` module can be used to implement support for the `gzip`, `deflate`, `br`, and `zstd` content-encoding mechanisms defined by HTTP.

The HTTP `Accept-Encoding` header is used within an HTTP request to identify the compression encodings accepted by the client. The `Content-Encoding` header is used to identify the compression encodings actually applied to a message.

The examples given below are drastically simplified to show the basic concept. Using `zlib` encoding can be expensive, and the results ought to be cached. See Memory usage tuning for more information on the speed/memory/compression tradeoffs involved in `zlib` usage.

    // Client request example
    import fs from 'node:fs';
    import zlib from 'node:zlib';
    import http from 'node:http';
    import process from 'node:process';
    import { pipeline } from 'node:stream';

    const request = http.get({ host: 'example.com',
                               path: '/',
                               port: 80,
                               headers: { 'Accept-Encoding': 'br,gzip,deflate,zstd' } });
    request.on('response', (response) => {
      const output = fs.createWriteStream('example.com_index.html');

      const onError = (err) => {
        if (err) {
          console.error('An error occurred:', err);
          process.exitCode = 1;
        }
      };

      switch (response.headers['content-encoding']) {
        case 'br':
          pipeline(response, zlib.createBrotliDecompress(), output, onError);
          break;
        // Or, just use zlib.createUnzip() to handle both of the following cases:
        case 'gzip':
          pipeline(response, zlib.createGunzip(), output, onError);
          break;
        case 'deflate':
          pipeline(response, zlib.createInflate(), output, onError);
          break;
        case 'zstd':
          pipeline(response, zlib.createZstdDecompress(), output, onError);
          break;
        default:
          pipeline(response, output, onError);
          break;
      }
    });
    // Client request example
    const zlib = require('node:zlib');
    const http = require('node:http');
    const fs = require('node:fs');
    const { pipeline } = require('node:stream');

    const request = http.get({ host: 'example.com',
                               path: '/',
                               port: 80,
                               headers: { 'Accept-Encoding': 'br,gzip,deflate,zstd' } });
    request.on('response', (response) => {
      const output = fs.createWriteStream('example.com_index.html');

      const onError = (err) => {
        if (err) {
          console.error('An error occurred:', err);
          process.exitCode = 1;
        }
      };

      switch (response.headers['content-encoding']) {
        case 'br':
          pipeline(response, zlib.createBrotliDecompress(), output, onError);
          break;
        // Or, just use zlib.createUnzip() to handle both of the following cases:
        case 'gzip':
          pipeline(response, zlib.createGunzip(), output, onError);
          break;
        case 'deflate':
          pipeline(response, zlib.createInflate(), output, onError);
          break;
        case 'zstd':
          pipeline(response, zlib.createZstdDecompress(), output, onError);
          break;
        default:
          pipeline(response, output, onError);
          break;
      }
    });
    javascript

    // server example
    // Running a gzip operation on every request is quite expensive.
    // It would be much more efficient to cache the compressed buffer.
    import zlib from 'node:zlib';
    import http from 'node:http';
    import fs from 'node:fs';
    import { pipeline } from 'node:stream';

    http.createServer((request, response) => {
      const raw = fs.createReadStream('index.html');
      // Store both a compressed and an uncompressed version of the resource.
      response.setHeader('Vary', 'Accept-Encoding');
      const acceptEncoding = request.headers['accept-encoding'] || '';

      const onError = (err) => {
        if (err) {
          // If an error occurs, there's not much we can do because
          // the server has already sent the 200 response code and
          // some amount of data has already been sent to the client.
          // The best we can do is terminate the response immediately
          // and log the error.
          response.end();
          console.error('An error occurred:', err);
        }
      };

      // Note: This is not a conformant accept-encoding parser.
      // See https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3
      if (/\bdeflate\b/.test(acceptEncoding)) {
        response.writeHead(200, { 'Content-Encoding': 'deflate' });
        pipeline(raw, zlib.createDeflate(), response, onError);
      } else if (/\bgzip\b/.test(acceptEncoding)) {
        response.writeHead(200, { 'Content-Encoding': 'gzip' });
        pipeline(raw, zlib.createGzip(), response, onError);
      } else if (/\bbr\b/.test(acceptEncoding)) {
        response.writeHead(200, { 'Content-Encoding': 'br' });
        pipeline(raw, zlib.createBrotliCompress(), response, onError);
      } else if (/\bzstd\b/.test(acceptEncoding)) {
        response.writeHead(200, { 'Content-Encoding': 'zstd' });
        pipeline(raw, zlib.createZstdCompress(), response, onError);
      } else {
        response.writeHead(200, {});
        pipeline(raw, response, onError);
      }
    }).listen(1337);
    // server example
    // Running a gzip operation on every request is quite expensive.
    // It would be much more efficient to cache the compressed buffer.
    const zlib = require('node:zlib');
    const http = require('node:http');
    const fs = require('node:fs');
    const { pipeline } = require('node:stream');

    http.createServer((request, response) => {
      const raw = fs.createReadStream('index.html');
      // Store both a compressed and an uncompressed version of the resource.
      response.setHeader('Vary', 'Accept-Encoding');
      const acceptEncoding = request.headers['accept-encoding'] || '';

      const onError = (err) => {
        if (err) {
          // If an error occurs, there's not much we can do because
          // the server has already sent the 200 response code and
          // some amount of data has already been sent to the client.
          // The best we can do is terminate the response immediately
          // and log the error.
          response.end();
          console.error('An error occurred:', err);
        }
      };

      // Note: This is not a conformant accept-encoding parser.
      // See https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3
      if (/\bdeflate\b/.test(acceptEncoding)) {
        response.writeHead(200, { 'Content-Encoding': 'deflate' });
        pipeline(raw, zlib.createDeflate(), response, onError);
      } else if (/\bgzip\b/.test(acceptEncoding)) {
        response.writeHead(200, { 'Content-Encoding': 'gzip' });
        pipeline(raw, zlib.createGzip(), response, onError);
      } else if (/\bbr\b/.test(acceptEncoding)) {
        response.writeHead(200, { 'Content-Encoding': 'br' });
        pipeline(raw, zlib.createBrotliCompress(), response, onError);
      } else if (/\bzstd\b/.test(acceptEncoding)) {
        response.writeHead(200, { 'Content-Encoding': 'zstd' });
        pipeline(raw, zlib.createZstdCompress(), response, onError);
      } else {
        response.writeHead(200, {});
        pipeline(raw, response, onError);
      }
    }).listen(1337);
    javascript

By default, the `zlib` methods will throw an error when decompressing truncated data. However, if it is known that the data is incomplete, or the desire is to inspect only the beginning of a compressed file, it is possible to suppress the default error handling by changing the flushing method that is used to decompress the last chunk of input data:

    // This is a truncated version of the buffer from the above examples
    const buffer = Buffer.from('eJzT0yMA', 'base64');

    zlib.unzip(
      buffer,
      // For Brotli, the equivalent is zlib.constants.BROTLI_OPERATION_FLUSH.
      // For Zstd, the equivalent is zlib.constants.ZSTD_e_flush.
      { finishFlush: zlib.constants.Z_SYNC_FLUSH },
      (err, buffer) => {
        if (err) {
          console.error('An error occurred:', err);
          process.exitCode = 1;
        }
        console.log(buffer.toString());
      });
    js

This will not change the behavior in other error-throwing situations, e.g. when the input data has an invalid format. Using this method, it will not be possible to determine whether the input ended prematurely or lacks the integrity checks, making it necessary to manually check that the decompressed result is valid.

### Memory usage tuning#

#### For zlib-based streams#

From `zlib/zconf.h`, modified for Node.js usage:

The memory requirements for deflate are (in bytes):

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

That is: 128K for `windowBits` = 15 + 128K for `memLevel` = 8 (default values) plus a few kilobytes for small objects.

For example, to reduce the default memory requirements from 256K to 128K, the options should be set to:

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

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 for small objects.

This is in addition to a single internal output slab buffer of size `chunkSize`, which defaults to 16K.

The speed of `zlib` compression is affected most dramatically by the `level` setting. A higher level will result in better compression, but will take longer to complete. A lower level will result in less compression, but will be much faster.

In general, greater memory usage options will mean that Node.js has to make fewer calls to `zlib` because it will be able to process more data on each `write` operation. So, this is another factor that affects the speed, at the cost of memory usage.

#### For Brotli-based streams#

There are equivalents to the zlib options for Brotli-based streams, although these options have different ranges than the zlib ones:

- zlib's `level` option matches Brotli's `BROTLI_PARAM_QUALITY` option.
- zlib's `windowBits` option matches Brotli's `BROTLI_PARAM_LGWIN` option.

See below for more details on Brotli-specific options.

#### For Zstd-based streams#

Stability: 1 - Experimental

There are equivalents to the zlib options for Zstd-based streams, although these options have different ranges than the zlib ones:

- zlib's `level` option matches Zstd's `ZSTD_c_compressionLevel` option.
- zlib's `windowBits` option matches Zstd's `ZSTD_c_windowLog` option.

See below for more details on Zstd-specific options.

### Flushing#

Calling `.flush()` on a compression stream will make `zlib` return as much output as currently possible. This may come at the cost of degraded compression quality, but can be useful when data needs to be available as soon as possible.

In the following example, `flush()` is used to write a compressed partial HTTP response to the client:

    import zlib from 'node:zlib';
    import http from 'node:http';
    import { pipeline } from 'node:stream';

    http.createServer((request, response) => {
      // For the sake of simplicity, the Accept-Encoding checks are omitted.
      response.writeHead(200, { 'content-encoding': 'gzip' });
      const output = zlib.createGzip();
      let i;

      pipeline(output, response, (err) => {
        if (err) {
          // If an error occurs, there's not much we can do because
          // the server has already sent the 200 response code and
          // some amount of data has already been sent to the client.
          // The best we can do is terminate the response immediately
          // and log the error.
          clearInterval(i);
          response.end();
          console.error('An error occurred:', err);
        }
      });

      i = setInterval(() => {
        output.write(`The current time is ${Date()}\n`, () => {
          // The data has been passed to zlib, but the compression algorithm may
          // have decided to buffer the data for more efficient compression.
          // Calling .flush() will make the data available as soon as the client
          // is ready to receive it.
          output.flush();
        });
      }, 1000);
    }).listen(1337);
    const zlib = require('node:zlib');
    const http = require('node:http');
    const { pipeline } = require('node:stream');

    http.createServer((request, response) => {
      // For the sake of simplicity, the Accept-Encoding checks are omitted.
      response.writeHead(200, { 'content-encoding': 'gzip' });
      const output = zlib.createGzip();
      let i;

      pipeline(output, response, (err) => {
        if (err) {
          // If an error occurs, there's not much we can do because
          // the server has already sent the 200 response code and
          // some amount of data has already been sent to the client.
          // The best we can do is terminate the response immediately
          // and log the error.
          clearInterval(i);
          response.end();
          console.error('An error occurred:', err);
        }
      });

      i = setInterval(() => {
        output.write(`The current time is ${Date()}\n`, () => {
          // The data has been passed to zlib, but the compression algorithm may
          // have decided to buffer the data for more efficient compression.
          // Calling .flush() will make the data available as soon as the client
          // is ready to receive it.
          output.flush();
        });
      }, 1000);
    }).listen(1337);
    javascript

### Constants#

Added in: v0.5.8

#### zlib constants#

All of the constants defined in `zlib.h` are also defined on `require('node:zlib').constants`. In the normal course of operations, it will not be necessary to use these constants. They are documented so that their presence is not surprising. This section is taken almost directly from the zlib documentation.

Previously, the constants were available directly from `require('node:zlib')`, for instance `zlib.Z_NO_FLUSH`. Accessing the constants directly from the module is currently still possible but is deprecated.

Allowed flush values.

- `zlib.constants.Z_NO_FLUSH`
- `zlib.constants.Z_PARTIAL_FLUSH`
- `zlib.constants.Z_SYNC_FLUSH`
- `zlib.constants.Z_FULL_FLUSH`
- `zlib.constants.Z_FINISH`
- `zlib.constants.Z_BLOCK`

Return codes for the compression/decompression functions. Negative values are errors, positive values are used for special but normal events.

- `zlib.constants.Z_OK`
- `zlib.constants.Z_STREAM_END`
- `zlib.constants.Z_NEED_DICT`
- `zlib.constants.Z_ERRNO`
- `zlib.constants.Z_STREAM_ERROR`
- `zlib.constants.Z_DATA_ERROR`
- `zlib.constants.Z_MEM_ERROR`
- `zlib.constants.Z_BUF_ERROR`
- `zlib.constants.Z_VERSION_ERROR`

Compression levels.

- `zlib.constants.Z_NO_COMPRESSION`
- `zlib.constants.Z_BEST_SPEED`
- `zlib.constants.Z_BEST_COMPRESSION`
- `zlib.constants.Z_DEFAULT_COMPRESSION`

Compression strategy.

- `zlib.constants.Z_FILTERED`
- `zlib.constants.Z_HUFFMAN_ONLY`
- `zlib.constants.Z_RLE`
- `zlib.constants.Z_FIXED`
- `zlib.constants.Z_DEFAULT_STRATEGY`

#### Brotli constants#

Added in: v11.7.0, v10.16.0

There are several options and other constants available for Brotli-based streams:

##### Flush operations#

The following values are valid flush operations for Brotli-based streams:

- `zlib.constants.BROTLI_OPERATION_PROCESS` (default for all operations)
- `zlib.constants.BROTLI_OPERATION_FLUSH` (default when calling `.flush()`)
- `zlib.constants.BROTLI_OPERATION_FINISH` (default for the last chunk)
- `zlib.constants.BROTLI_OPERATION_EMIT_METADATA`
  - This particular operation may be hard to use in a Node.js context, as the streaming layer makes it hard to know which data will end up in this frame. Also, there is currently no way to consume this data through the Node.js API.

##### Compressor options#

There are several options that can be set on Brotli encoders, affecting compression efficiency and speed. Both the keys and the values can be accessed as properties of the `zlib.constants` object.

The most important options are:

- `BROTLI_PARAM_MODE`
  - `BROTLI_MODE_GENERIC` (default)
  - `BROTLI_MODE_TEXT`, adjusted for UTF-8 text
  - `BROTLI_MODE_FONT`, adjusted for WOFF 2.0 fonts
- `BROTLI_PARAM_QUALITY`
  - Ranges from `BROTLI_MIN_QUALITY` to `BROTLI_MAX_QUALITY`, with a default of `BROTLI_DEFAULT_QUALITY`.
- `BROTLI_PARAM_SIZE_HINT`
  - Integer value representing the expected input size; defaults to `0` for an unknown input size.

The following flags can be set for advanced control over the compression algorithm and memory usage tuning:

- `BROTLI_PARAM_LGWIN`
  - Ranges from `BROTLI_MIN_WINDOW_BITS` to `BROTLI_MAX_WINDOW_BITS`, with a default of `BROTLI_DEFAULT_WINDOW`, or up to `BROTLI_LARGE_MAX_WINDOW_BITS` if the `BROTLI_PARAM_LARGE_WINDOW` flag is set.
- `BROTLI_PARAM_LGBLOCK`
  - Ranges from `BROTLI_MIN_INPUT_BLOCK_BITS` to `BROTLI_MAX_INPUT_BLOCK_BITS`.
- `BROTLI_PARAM_DISABLE_LITERAL_CONTEXT_MODELING`
  - Boolean flag that decreases compression ratio in favour of decompression speed.
- `BROTLI_PARAM_LARGE_WINDOW`
  - Boolean flag enabling “Large Window Brotli” mode (not compatible with the Brotli format as standardized in RFC 7932).
- `BROTLI_PARAM_NPOSTFIX`
  - Ranges from `0` to `BROTLI_MAX_NPOSTFIX`.
- `BROTLI_PARAM_NDIRECT`
  - Ranges from `0` to `15 << NPOSTFIX` in steps of `1 << NPOSTFIX`.

##### Decompressor options#

These advanced options are available for controlling decompression:

- `BROTLI_DECODER_PARAM_DISABLE_RING_BUFFER_REALLOCATION`
  - Boolean flag that affects internal memory allocation patterns.
- `BROTLI_DECODER_PARAM_LARGE_WINDOW`
  - Boolean flag enabling “Large Window Brotli” mode (not compatible with the Brotli format as standardized in RFC 7932).

#### Zstd constants#

Added in: v23.8.0, v22.15.0

Stability: 1 - Experimental

There are several options and other constants available for Zstd-based streams:

##### Flush operations#

The following values are valid flush operations for Zstd-based streams:

- `zlib.constants.ZSTD_e_continue` (default for all operations)
- `zlib.constants.ZSTD_e_flush` (default when calling `.flush()`)
- `zlib.constants.ZSTD_e_end` (default for the last chunk)

##### Compressor options#

There are several options that can be set on Zstd encoders, affecting compression efficiency and speed. Both the keys and the values can be accessed as properties of the `zlib.constants` object.

The most important options are:

- `ZSTD_c_compressionLevel`
  - Set compression parameters according to pre-defined cLevel table. Default level is ZSTD_CLEVEL_DEFAULT==3.
- `ZSTD_c_strategy`
  - Select the compression strategy.
  - Possible values are listed in the strategy options section below.

##### Strategy options#

The following constants can be used as values for the `ZSTD_c_strategy` parameter:

- `zlib.constants.ZSTD_fast`
- `zlib.constants.ZSTD_dfast`
- `zlib.constants.ZSTD_greedy`
- `zlib.constants.ZSTD_lazy`
- `zlib.constants.ZSTD_lazy2`
- `zlib.constants.ZSTD_btlazy2`
- `zlib.constants.ZSTD_btopt`
- `zlib.constants.ZSTD_btultra`
- `zlib.constants.ZSTD_btultra2`

Example:

    const stream = zlib.createZstdCompress({
      params: {
        [zlib.constants.ZSTD_c_strategy]: zlib.constants.ZSTD_btultra,
      },
    });
    js

##### Pledged Source Size#

It's possible to specify the expected total size of the uncompressed input via `opts.pledgedSrcSize`, which must be a non-negative safe integer. If the size doesn't match at the end of the input, compression will fail with the code `ZSTD_error_srcSize_wrong`.

##### Decompressor options#

These advanced options are available for controlling decompression:

- `ZSTD_d_windowLogMax`
  - Select a size limit (in power of 2) beyond which the streaming API will refuse to allocate memory buffer in order to protect the host from unreasonable memory requirements.

### Class: `Options`#

Added in: v0.11.1
History

Version | Changes
--- | ---
v26.5.0 | The `rejectGarbageAfterEnd` option was added.
v14.5.0, v12.19.0 | The `maxOutputLength` option is supported now.
v9.4.0 | The `dictionary` option can be an `ArrayBuffer`.
v8.0.0 | The `dictionary` option can be an `Uint8Array` now.
v5.11.0 | The `finishFlush` option is supported now.

Each zlib-based class takes an `options` object. No options are required.

Some options are only relevant when compressing and are ignored by the decompression classes.

- `flush` `<integer>` Default: `zlib.constants.Z_NO_FLUSH`
- `finishFlush` `<integer>` Default: `zlib.constants.Z_FINISH`
- `chunkSize` `<integer>` Default: `16 * 1024`
- `windowBits` `<integer>`
- `level` `<integer>` (compression only)
- `memLevel` `<integer>` (compression only)
- `strategy` `<integer>` (compression only)
- `dictionary` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` (deflate/inflate only, empty dictionary by default)
- `info` `<boolean>` (If `true`, returns an object with `buffer` and `engine`.)
- `maxOutputLength` `<integer>` Limits output size when using convenience methods. Default: `buffer.kMaxLength`
- `rejectGarbageAfterEnd` `<boolean>` If `true`, decompression fails when trailing input is detected after the end of the compressed stream. This includes unreadable bytes and, when decompressing gzip, additional gzip members following the first member. Default: `false`

See the `deflateInit2` and `inflateInit2` documentation for more information.

### Class: `BrotliOptions`#

Added in: v11.7.0
History

Version | Changes
--- | ---
v26.5.0 | The `rejectGarbageAfterEnd` option was added.
v14.5.0, v12.19.0 | The `maxOutputLength` option is supported now.

Each Brotli-based class takes an `options` object. All options are optional.

- `flush` `<integer>` Default: `zlib.constants.BROTLI_OPERATION_PROCESS`
- `finishFlush` `<integer>` Default: `zlib.constants.BROTLI_OPERATION_FINISH`
- `chunkSize` `<integer>` Default: `16 * 1024`
- `params` `<Object>` Key-value object containing indexed Brotli parameters.
- `maxOutputLength` `<integer>` Limits output size when using convenience methods. Default: `buffer.kMaxLength`
- `info` `<boolean>` If `true`, returns an object with `buffer` and `engine`. Default: `false`
- `rejectGarbageAfterEnd` `<boolean>` If `true`, decompression fails when input remains after the first complete compressed stream. Default: `false`

For example:

    const stream = zlib.createBrotliCompress({
      chunkSize: 32 * 1024,
      params: {
        [zlib.constants.BROTLI_PARAM_MODE]: zlib.constants.BROTLI_MODE_TEXT,
        [zlib.constants.BROTLI_PARAM_QUALITY]: 4,
        [zlib.constants.BROTLI_PARAM_SIZE_HINT]: fs.statSync(inputFile).size,
      },
    });
    js

### Class: `zlib.BrotliCompress`#

Added in: v11.7.0, v10.16.0

- Extends: `ZlibBase`

Compress data using the Brotli algorithm.

### Class: `zlib.BrotliDecompress`#

Added in: v11.7.0, v10.16.0

- Extends: `ZlibBase`

Decompress data using the Brotli algorithm.

### Class: `zlib.Deflate`#

Added in: v0.5.8

- Extends: `ZlibBase`

Compress data using deflate.

### Class: `zlib.DeflateRaw`#

Added in: v0.5.8

- Extends: `ZlibBase`

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

### Class: `zlib.Gunzip`#

Added in: v0.5.8
History

Version | Changes
--- | ---
v6.0.0 | Trailing garbage at the end of the input stream will now result in an `'error'` event.
v5.9.0 | Multiple concatenated gzip file members are supported now.
v5.0.0 | A truncated input stream will now result in an `'error'` event.

- Extends: `ZlibBase`

Decompress a gzip stream.

### Class: `zlib.Gzip`#

Added in: v0.5.8

- Extends: `ZlibBase`

Compress data using gzip.

### Class: `zlib.Inflate`#

Added in: v0.5.8
History

Version | Changes
--- | ---
v5.0.0 | A truncated input stream will now result in an `'error'` event.

- Extends: `ZlibBase`

Decompress a deflate stream.

### Class: `zlib.InflateRaw`#

Added in: v0.5.8
History

Version | Changes
--- | ---
v6.8.0 | Custom dictionaries are now supported by `InflateRaw`.
v5.0.0 | A truncated input stream will now result in an `'error'` event.

- Extends: `ZlibBase`

Decompress a raw deflate stream.

### Class: `zlib.Unzip`#

Added in: v0.5.8

- Extends: `ZlibBase`

Decompress either a Gzip- or Deflate-compressed stream by auto-detecting the header.

### Class: `zlib.ZipBuffer`#

Added in: v26.8.0

Stability: 1.0 - Early development

The ZIP archive API is experimental. Using any part of it (this class among them) emits an experimental warning the first time; merely importing `node:zlib` does not.

An in-memory, zero-copy view over the entries of a ZIP archive already held in a `Buffer`, `TypedArray`, `DataView`, or `ArrayBuffer`. Its set of entries can be edited - entries added or removed - but, unlike `ZipFile`, those edits are not written into the source buffer: a newly added entry is held as a separate in-memory `ZipEntry` (the passed buffer is a fixed-size view with no room to append to), and removal just drops the entry from `ZipBuffer`'s index. The original bytes are never modified. `zipBuffer.toBuffer()` serializes the current set of entries into a fresh archive.

`ZipBuffer` does not copy the archive you hand it. It keeps a view onto that memory and reads each entry's content lazily and directly from it, which is what makes construction cheap regardless of archive size. The trade-off is that you must not modify or reuse that memory - including the `ArrayBuffer` backing a `TypedArray`/`DataView` - while the `ZipBuffer`, or any `ZipEntry` obtained from it, is still in use: a later read would observe the change and may fail or return corrupt data. Pass a copy (for example `Buffer.from(source)`) if the source might be mutated or reused.

`add()` and `toBuffer()` each have a `*Sync` counterpart (`addSync()`, `toBufferSync()`) that performs the same compression work synchronously. As with the synchronous `node:fs` APIs, these block the Node.js event loop and further JavaScript execution until the operation completes; use them only where synchronous execution is appropriate (for example, short-lived scripts or startup code), not in code that must stay responsive.

    import { ZipBuffer } from 'node:zlib';
    import { readFileSync, writeFileSync } from 'node:fs';
    import { Buffer } from 'node:buffer';

    const zip = new ZipBuffer(readFileSync('archive.zip'));
    for (const [name, entry] of zip) {
      console.log(name, entry.size);
    }
    await zip.add('hello.txt', Buffer.from('Hello, world!'));
    zip.delete('unwanted.txt');
    writeFileSync('archive.zip', await zip.toBuffer());
    const { ZipBuffer } = require('node:zlib');
    const { readFileSync, writeFileSync } = require('node:fs');

    async function main() {
      const zip = new ZipBuffer(readFileSync('archive.zip'));
      for (const [name, entry] of zip) {
        console.log(name, entry.size);
      }
      await zip.add('hello.txt', Buffer.from('Hello, world!'));
      zip.delete('unwanted.txt');
      writeFileSync('archive.zip', await zip.toBuffer());
    }
    main();
    javascript

#### `new zlib.ZipBuffer(buffer)`#

Added in: v26.8.0

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` A complete ZIP archive.

Parses the archive's central directory. Throws an `ERR_ZIP_INVALID_ARCHIVE` or `ERR_ZIP_UNSUPPORTED_FEATURE` error if `buffer` is not a well-formed, supported archive.

`buffer` is not copied: the `ZipBuffer` retains a zero-copy view of it (for a `TypedArray`, `DataView`, or `ArrayBuffer`, of the underlying `ArrayBuffer`) and reads entry content directly from it on demand. Do not mutate or reuse that memory while the `ZipBuffer` or any entry read from it is still live; pass a copy if it might change.

#### `zipBuffer.add(filename, data[, options])`#

Added in: v26.8.0

- `filename` `<string>` The entry's name within the archive. A trailing `/` marks a directory entry.
- `data` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` The entry's complete, uncompressed content.
- `options` `<Object>` See `zlib.ZipEntry.create()`.
- Returns: `<Promise>` Fulfilled with the created `<ZipEntry>`.

Equivalent to `zipBuffer.addEntry(await zlib.ZipEntry.create(filename, data, options))`.

#### `zipBuffer.addSync(filename, data[, options])`#

Added in: v26.8.0

- `filename` `<string>` The entry's name within the archive. A trailing `/` marks a directory entry.
- `data` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` The entry's complete, uncompressed content.
- `options` `<Object>` See `zlib.ZipEntry.createSync()`.
- Returns: `<ZipEntry>` The created entry.

The synchronous version of `zipBuffer.add()`. Equivalent to `zipBuffer.addEntry(zlib.ZipEntry.createSync(filename, data, options))`.

#### `zipBuffer.addEntry(entry)`#

Added in: v26.8.0

- `entry` `<ZipEntry>`
- Returns: `<ZipEntry>` `entry`.

Adds an already-built entry, keyed by its own `zipEntry.name`. Replaces any existing entry of that name.

#### `zipBuffer.clear()`#

Added in: v26.8.0

Removes every entry.

#### `zipBuffer.comment`#

Added in: v26.8.0

- Type: `<string>`

The archive-level comment, preserved byte-for-byte across `zipBuffer.toBuffer()` calls unless overridden. The bytes are decoded as UTF-8 when they are valid UTF-8 and as CP437 otherwise (the field carries no encoding flag of its own).

#### `zipBuffer.delete(name)`#

Added in: v26.8.0

- `name` `<string>`
- Returns: `<boolean>` `true` if an entry named `name` existed and was removed.

#### `zipBuffer.entries()`#

Added in: v26.8.0

- Returns: `<Iterator>` of `[name, entry]` pairs, where `entry` is a `ZipEntry`.

#### `zipBuffer.forEach(callback[, thisArg])`#

Added in: v26.8.0

- `callback` `<Function>`
- `thisArg` `<any>`

Calls `callback` once for each entry, in the order the archive lists them.

#### `zipBuffer.get(name)`#

Added in: v26.8.0

- `name` `<string>`
- Returns: `<ZipEntry>`

Throws `ERR_ZIP_ENTRY_NOT_FOUND` if the archive has no entry named `name`.

#### `zipBuffer.has(name)`#

Added in: v26.8.0

- `name` `<string>`
- Returns: `<boolean>`

#### `zipBuffer.keys()`#

Added in: v26.8.0

- Returns: `<Iterator>` of entry names.

#### `zipBuffer.size`#

Added in: v26.8.0

- Type: `<number>`

The number of entries in the archive.

#### `zipBuffer.toBuffer([options])`#

Added in: v26.8.0

- `options` `<string>` | `<Object>` An archive comment, as a shorthand for `{ comment: options }`.
  - `comment` `<string>` An archive comment. Default: `zipBuffer.comment`.
  - `baseOffset` `<number>` Shifts every offset the archive records by this many bytes, so the serialized archive is self-describing even when it is written somewhere other than the start of its eventual file - for example, after `baseOffset` bytes of other content already written to the same output. Default: `0`.
- Returns: `<Promise>` Fulfilled with a `<Buffer>` containing the serialized archive.

Serializes the current set of entries - in the order they were added or read - into a fresh archive, switching to Zip64 structures automatically as needed (see `zlib.createZipArchive()`).

#### `zipBuffer.toBufferSync([options])`#

Added in: v26.8.0

- `options` `<string>` | `<Object>` See `zipBuffer.toBuffer()`.
- Returns: `<Buffer>` The serialized archive.

The synchronous version of `zipBuffer.toBuffer()` (see `zlib.createZipArchiveSync()`).

#### `zipBuffer.values()`#

Added in: v26.8.0

- Returns: `<Iterator>` of `ZipEntry`.

#### `zipBuffer.writable`#

Added in: v26.8.0

- Type: `<boolean>`

Always `true`.

### Class: `zlib.ZipEntry`#

Added in: v26.8.0

Stability: 1.0 - Early development

The ZIP archive API is experimental. Using any part of it (this class among them) emits an experimental warning the first time; merely importing `node:zlib` does not.

A single file or directory inside a ZIP archive. Instances are produced by `ZipBuffer` and `ZipFile`, or created directly for writing with `ZipEntry.create()`/`ZipEntry.createStream()`.

`create()` and `content()` each have a `*Sync` counterpart (the streaming `contentIterator()` does not). As with the synchronous `node:fs` APIs, these block the Node.js event loop and further JavaScript execution until the operation (including any deflate/inflate pass) completes; use them only where synchronous execution is appropriate (for example, short-lived scripts or startup code), not in code that must stay responsive.

#### Static method: `zlib.ZipEntry.create(filename, data[, options])`#

Added in: v26.8.0

- `filename` `<string>` The entry's name within the archive. A trailing `/` marks a directory entry.
- `data` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` The entry's complete, uncompressed content. Must be empty when `filename` names a directory.
- `options` `<Object>`
  - `comment` `<string>` An entry comment.
  - `mode` `<integer>` Unix permission bits. Default: `0o644` (`0o755` for directories).
  - `modified` `<Date>` The entry's modification time. Default: the current time.
  - `method` `<string>` One of `'deflate'`, `'store'`, or `'zstd'`. Default: `'deflate'`, except for directories and empty content, which are always stored.
- Returns: `<Promise>` Fulfilled with a `<ZipEntry>`.

Compresses `data` (unless `method` is `'store'`, or compression would not reduce its size) and computes its CRC-32.

When the entry ends up stored uncompressed (because `method` is `'store'`, or because compression would not reduce the size), the entry retains a zero-copy view of `data` rather than a copy, and its CRC-32 has already been recorded. Do not mutate `data` after creating the entry; pass a copy if it might change.

The MS-DOS date/time fields ZIP uses for `modified` have 2-second resolution and no time zone. When `modified` does not fall on a whole 2-second boundary, an Info-ZIP extended-timestamp extra field is written as well, recording the whole (UTC) second so the time round-trips more precisely (see `zipEntry.modified`). This applies to every entry-creation path.

#### Static method: `zlib.ZipEntry.createStream(filename, source[, options])`#

Added in: v26.8.0

- `filename` `<string>` The entry's name within the archive. Must not end in `/`.
- `source` `<AsyncIterable>` Yields the entry's uncompressed content as `Uint8Array` chunks.
- `options` `<Object>`
  - `comment` `<string>` An entry comment.
  - `mode` `<integer>` Unix permission bits. Default: `0o644`.
  - `modified` `<Date>` The entry's modification time. Default: the current time.
  - `method` `<string>` One of `'deflate'`, `'store'`, or `'zstd'`. Default: `'deflate'`.
- Returns: `<ZipEntry>`

Creates an entry whose content is compressed on the fly as it is serialized by `zlib.createZipArchive()`, without buffering `source` in memory. Its `size`, `compressedSize`, and `crc32` only become available once serialization has finished. There is no synchronous counterpart: streaming entries only make sense with an asynchronous, incrementally-produced `source`.

`source` is drained exactly once, during serialization. Until that happens the entry has no readable content, so `zipEntry.content()`, `zipEntry.contentSync()`, and `zipEntry.contentIterator()` throw `ERR_INVALID_STATE`. If the entry is serialized by adding it to a writable `ZipFile` with `zipFile.addEntry()` (or `addEntrySync()`), it is then promoted in place to a file-backed entry pointing at the copy just written, so it becomes readable (and can be serialized again) for as long as that `ZipFile` stays open. Serializing it any other way (for example directly through `zlib.createZipArchive()`) leaves it spent and unreadable.

Because `source` may hold an operating-system resource (a file read stream, say), a streaming entry is disposable: its `Symbol.dispose` and `Symbol.asyncDispose` methods destroy `source` if it has not been consumed. An entry passed to an archive is disposed by that archive (see `zlib.createZipArchive()`); dispose an entry directly only when it was built but never handed to one. Disposal is a no-op for non-streaming entries - in particular a file-backed entry never closes the `ZipFile` descriptor it borrows.

#### Static method: `zlib.ZipEntry.createSymlink(filename, target[, options])`#

Added in: v26.8.0

- `filename` `<string>` The entry's name within the archive.
- `target` `<string>` The symbolic link's target path.
- `options` `<Object>`
  - `comment` `<string>` An entry comment.
  - `mode` `<integer>` Unix permission bits. Default: `0o777`.
  - `modified` `<Date>` The entry's modification time. Default: the current time.
- Returns: `<ZipEntry>`

Creates a symbolic-link entry: a stored entry whose content is `target` and whose Unix mode type bits mark it as a symlink, so `zipEntry.isSymlink` is `true` when it is read back. Extraction tools that honor symlink entries recreate the link; treat `target` as untrusted (see `zipEntry.name` on path safety).

#### Static method: `zlib.ZipEntry.createSync(filename, data[, options])`#

Added in: v26.8.0

- `filename` `<string>` The entry's name within the archive. A trailing `/` marks a directory entry.
- `data` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` The entry's complete, uncompressed content. Must be empty when `filename` names a directory.
- `options` `<Object>` See `zlib.ZipEntry.create()`.
- Returns: `<ZipEntry>`

The synchronous version of `zlib.ZipEntry.create()`.

#### Static method: `zlib.ZipEntry.read(buffer)`#

Added in: v26.8.0

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` A complete ZIP archive.
- Returns: `<Iterator>` of `<ZipEntry>`.

Parses every entry out of `buffer` directly, without indexing it into a `ZipBuffer`. Like `ZipBuffer`, the yielded entries hold zero-copy views of `buffer` rather than copies of their content, so the same rule applies: do not mutate or reuse `buffer` while any of them is still in use.

#### `zipEntry.comment`#

Added in: v26.8.0

- Type: `<string>`

#### `zipEntry.compressed`#

Added in: v26.8.0

- Type: `<boolean>`

`true` if the entry's content is stored in compressed form (any compression method, currently deflate or Zstandard); `false` if it is stored uncompressed.

#### `zipEntry.compressedSize`#

Added in: v26.8.0

- Type: `<number>`

#### `zipEntry.content([options])`#

Added in: v26.8.0

- `options` `<Object>`
  - `verify` `<boolean>` Verify the entry's CRC-32 checksum. Default: `true`.
  - `maxSize` `<number>` Reject content declaring more than this many uncompressed bytes, before allocating anything. Default: `zlib.getMaxZipContentSize()`.
- Returns: `<Promise>` Fulfilled with a `<Buffer>` containing the entry's decompressed content. The buffer is a fresh copy that shares no memory with the archive or with data the entry was created from.

Throws an `ERR_ZIP_ENTRY_TOO_LARGE` error if the entry's declared size exceeds `maxSize`, an `ERR_ZIP_ENTRY_CORRUPT` error if the content fails CRC-32 verification or does not match its declared size, and an `ERR_INVALID_STATE` error for a streaming entry (`zlib.ZipEntry.createStream()`) whose content is not yet available (see that method for when a streaming entry becomes readable).

#### `zipEntry.contentSync([options])`#

Added in: v26.8.0

- `options` `<Object>` See `zipEntry.content()`.
- Returns: `<Buffer>` The entry's decompressed content.

The synchronous version of `zipEntry.content()`.

#### `zipEntry.contentIterator([options])`#

Added in: v26.8.0

- `options` `<Object>`
  - `verify` `<boolean>` Verify the entry's CRC-32 checksum. Default: `true`.
  - `maxSize` `<number>` Reject content declaring more than this many uncompressed bytes, before decompressing anything. Default: no limit.
- Returns: `<AsyncIterator>` of `<Buffer>` chunks of the entry's decompressed content.

Unlike `zipEntry.content()`, this does not buffer the whole member in memory. For a file-backed entry (one returned by `zipFile.get()`) the compressed bytes are read from disk as the iterator is consumed and nothing is retained; the entry is valid only while its `ZipFile` is open.

Because streaming is the bounded-memory path for arbitrarily large members, it is not capped by `zlib.getMaxZipContentSize()` the way `zipEntry.content()` is - that default guards a single large allocation, which streaming never makes. Output is still bounded per chunk to the declared uncompressed size; pass `maxSize` to impose an explicit ceiling.

For an in-memory entry stored without compression, the yielded chunks are zero-copy views of the entry's retained content (see `zipEntry.rawContent`); do not mutate them.

The yielded chunks are provisional until the iterator completes. CRC-32 verification (and the final declared-size check) can only run once every byte has been read, so a corrupt or truncated entry is reported by the iterator throwing after the last chunk, not before the first. Each chunk is still bounded so the total never exceeds the declared size or `maxSize`, but a consumer that must not act on unverified bytes should buffer them (or use `zipEntry.content()`, which verifies before returning anything) rather than processing chunks as they arrive.

#### `zipEntry.crc32`#

Added in: v26.8.0

- Type: `<number>`

#### `zipEntry.flags`#

Added in: v26.8.0

- Type: `<number>`

The entry's raw general-purpose bit flag.

#### `zipEntry.isDirectory`#

Added in: v26.8.0

- Type: `<boolean>`

`true` if the entry is a directory (its name ends with `/`).

#### `zipEntry.isFile`#

Added in: v26.8.0

- Type: `<boolean>`

`true` if the entry is a regular file — that is, neither a directory nor a symbolic link.

#### `zipEntry.isSymlink`#

Added in: v26.8.0

- Type: `<boolean>`

`true` if the entry is a symbolic link (its Unix mode type bits are `S_IFLNK`); its content is the link target. Always `false` for archives not written on a Unix-like system. When extracting, treat a symlink's target as untrusted — see `zipEntry.name` on path safety.

#### `zipEntry.mode`#

Added in: v26.8.0

- Type: `<number>`

The entry's Unix mode permission bits, including the setuid, setgid, and sticky bits (the low 12 bits, `0o7777`), or `0` if the archive was not written on a Unix-like system. The file-type bits are not included here; use `zipEntry.isDirectory` / `zipEntry.isSymlink` for the type.

#### `zipEntry.modified`#

Added in: v26.8.0

- Type: `<Date>`

The entry's last-modification time. When the archive carries a higher-fidelity timestamp in an extra field — an NTFS (`0x000a`), Info-ZIP extended (`0x5455`), or Info-ZIP Unix (`0x5855`) field, as most modern tools write — that absolute (UTC) time is used; otherwise the coarse, local-time MS-DOS date/time field (2-second resolution) is used.

Some tools store their high-fidelity timestamp only in the local file header, so on a file-backed entry (one returned by `zipFile.get()`) the first read of this property may perform a small synchronous positioned disk read to resolve that header. If that read fails, the value silently falls back to the central-directory data.

#### `zipEntry.method`#

Added in: v26.8.0

- Type: `<number>`

The entry's raw compression method: `0` for stored, `8` for deflate, `93` for Zstandard.

#### `zipEntry.name`#

Added in: v26.8.0

- Type: `<string>`

The entry's name, decoded from the central directory, which is treated as authoritative — a local file header that disagrees is ignored, so a mismatched-header ("ZIP-confusion") archive cannot make `name` disagree with what is read. The bytes are decoded from a valid Info-ZIP Unicode Path extra field (`0x7075`) when one is present; otherwise as UTF-8 when the language-encoding flag (general-purpose bit 11) is set or the bytes are valid UTF-8 (plenty of tools wrote UTF-8 names without ever setting the flag); and as CP437 — the historical default — only when they are not. See `zipEntry.nameBuffer` for the raw bytes.

The name is returned verbatim: it is never normalized, and a name containing `..`, a leading `/`, a drive letter, or backslashes is neither rewritten nor rejected. A `ZipFile`/`ZipBuffer` never writes to disk, so guarding against path traversal ("Zip Slip") when extracting is the caller's responsibility.

#### `zipEntry.nameBuffer`#

Added in: v26.8.0

- Type: `<Buffer>`

The entry's raw name bytes, before any character decoding. Useful when the archive's names are in an encoding other than UTF-8 or CP437 and the caller wants to decode them itself.

#### `zipEntry.rawContent`#

Added in: v26.8.0

- Type: `<Buffer>` | `<null>`

The entry's raw (still compressed, if applicable) content when it is held in memory, or `null` when there is no in-memory buffer to expose - for an entry created with `zlib.ZipEntry.createStream()`, or a file-backed entry returned by `zipFile.get()`, whose bytes are read from disk on demand rather than retained. Use `zipEntry.content()` or `zipEntry.contentIterator()` to read a file-backed entry.

#### `zipEntry.size`#

Added in: v26.8.0

- Type: `<number>`

The entry's uncompressed size, in bytes.

### Class: `zlib.ZipFile`#

Added in: v26.8.0

Stability: 1.0 - Early development

The ZIP archive API is experimental. Using any part of it (this class among them) emits an experimental warning the first time; merely importing `node:zlib` does not.

A random-access view over the entries of a ZIP archive on disk. Only the archive's tail and central directory are read up front; member content is read from disk lazily, on demand. Writable when opened with `{ writable: true }`: `zipFile.addEntry()`/`zipFile.add()` append the new member's data where the central directory used to be, then rewrite the central directory immediately after it; `zipFile.delete()` just rewrites the central directory. Both mean the file is altered as soon as the method's returned `Promise` fulfills. Deleted or replaced members are left behind as dead space; `zipFile.compact()` produces a stream with none.

These in-place edits are not crash-atomic. Rewriting the central directory happens in place, so a write that fails partway - the disk fills, the device disconnects, the process is killed - can leave the archive on disk with a partial or missing central directory, i.e. unreadable, even though the member data before it is intact. The rejected call surfaces the underlying error and the `ZipFile` object is left usable (its in-memory view is not discarded, so a caller can attempt recovery - for example re-writing the entries elsewhere with `zipFile.compact()`), but that in-memory view may no longer match the bytes on disk. Write to a copy, or `compact()` into a fresh file, when durability across a failure matters.

Every method has a `*Sync` counterpart. As with the synchronous `node:fs` APIs, these block the Node.js event loop and further JavaScript execution until the operation completes; use them only where synchronous execution is appropriate (for example, short-lived scripts or startup code), not in code that must stay responsive. A synchronous method throws `ERR_INVALID_STATE` if called while an asynchronous `add()`, `addEntry()`, `delete()`, or `close()` on the same `ZipFile` has not settled yet, since letting the two interleave could corrupt the archive.

    import { ZipFile } from 'node:zlib';
    import { Buffer } from 'node:buffer';

    const zip = await ZipFile.open('archive.zip', { writable: true });
    try {
      const entry = await zip.get('member.txt');
      console.log((await entry.content()).toString());
      for await (const chunk of await zip.stream('huge.bin')) {
        // Process each chunk without buffering the whole member.
      }
      await zip.add('new.txt', Buffer.from('hello'));
      await zip.delete('unwanted.txt');
    } finally {
      await zip.close();
    }
    const { ZipFile } = require('node:zlib');

    async function main() {
      const zip = await ZipFile.open('archive.zip', { writable: true });
      try {
        const entry = await zip.get('member.txt');
        console.log((await entry.content()).toString());
        for await (const chunk of await zip.stream('huge.bin')) {
          // Process each chunk without buffering the whole member.
        }
        await zip.add('new.txt', Buffer.from('hello'));
        await zip.delete('unwanted.txt');
      } finally {
        await zip.close();
      }
    }
    main();
    javascript

#### Static method: `zlib.ZipFile.open(filename[, options])`#

Added in: v26.8.0

- `filename` `<string>`
- `options` `<Object>`
  - `writable` `<boolean>` Open the underlying file for both reading and writing (`'r+'`), enabling `zipFile.addEntry()`/`zipFile.add()`/ `zipFile.delete()`. Default: `false`.
- Returns: `<Promise>` Fulfilled with a `<ZipFile>`.

Throws an `ERR_ZIP_ARCHIVE_TOO_LARGE` error if the archive's central directory is too large to buffer in memory.

#### Static method: `zlib.ZipFile.openSync(filename[, options])`#

Added in: v26.8.0

- `filename` `<string>`
- `options` `<Object>` See `zlib.ZipFile.open()`.
- Returns: `<ZipFile>`

The synchronous version of `zlib.ZipFile.open()`.

#### `zipFile.add(filename, data[, options])`#

Added in: v26.8.0

- `filename` `<string>` The entry's name within the archive. A trailing `/` marks a directory entry.
- `data` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` The entry's complete, uncompressed content.
- `options` `<Object>` See `zlib.ZipEntry.create()`.
- Returns: `<Promise>` Fulfilled with the created `<ZipEntry>`.

Equivalent to `zipFile.addEntry(await zlib.ZipEntry.create(filename, data, options))`.

#### `zipFile.addEntry(entry)`#

Added in: v26.8.0

- `entry` `<ZipEntry>`
- Returns: `<Promise>` Fulfilled with `entry`.

Writes `entry` where the central directory currently starts, then rewrites the central directory to include it, replacing any existing entry of the same name. Throws `ERR_ZIP_NOT_WRITABLE` if the `ZipFile` was not opened with `{ writable: true }`.

The returned (same) `entry` is left readable: a streaming entry created with `zlib.ZipEntry.createStream()`, which would otherwise be spent once serialized, is promoted in place to a file-backed entry pointing at the copy just written (valid while this `ZipFile` is open). In-memory entries keep their own buffer unchanged.

#### `zipFile.addEntrySync(entry)`#

Added in: v26.8.0

- `entry` `<ZipEntry>`
- Returns: `<ZipEntry>` `entry`.

The synchronous version of `zipFile.addEntry()`. `entry` must not be a pending streaming entry (one created with `zlib.ZipEntry.createStream()`) - there is no synchronous way to drain its asynchronous source.

#### `zipFile.addSync(filename, data[, options])`#

Added in: v26.8.0

- `filename` `<string>` The entry's name within the archive. A trailing `/` marks a directory entry.
- `data` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` The entry's complete, uncompressed content.
- `options` `<Object>` See `zlib.ZipEntry.createSync()`.
- Returns: `<ZipEntry>` The created entry.

The synchronous version of `zipFile.add()`. Equivalent to `zipFile.addEntrySync(zlib.ZipEntry.createSync(filename, data, options))`.

#### `zipFile.close()`#

Added in: v26.8.0

- Returns: `<Promise>`

Closes the underlying file handle.

Closing does not invalidate outstanding objects: `ZipEntry` objects previously returned by `zipFile.get()` and the `ZipFile`'s own methods will fail with system-level errors (for example `EBADF`) if used after close, rather than a dedicated Node.js error code. The same applies to `zipFile.closeSync()`.

#### `zipFile.closeSync()`#

Added in: v26.8.0

The synchronous version of `zipFile.close()`.

#### `zipFile.comment`#

Added in: v26.8.0

- Type: `<string>`

The archive-level comment, preserved byte-for-byte across `zipFile.addEntry()`/`zipFile.delete()` calls. The bytes are decoded as UTF-8 when they are valid UTF-8 and as CP437 otherwise (the field carries no encoding flag of its own).

#### `zipFile.compact([comment])`#

Added in: v26.8.0

- `comment` `<string>` An archive comment. Default: `zipFile.comment`.
- Returns: `<stream.Readable>` A stream of the currently live entries, serialized as a fresh archive with no dead space left by prior `zipFile.addEntry()`/`zipFile.delete()` calls.

Does not modify the open file; pipe the result into a new one:

    import { createWriteStream } from 'node:fs';
    zip.compact().pipe(createWriteStream('compacted.zip'));
    mjs

#### `zipFile.compactSync([comment])`#

Added in: v26.8.0

- `comment` `<string>` An archive comment. Default: `zipFile.comment`.
- Returns: `<Buffer>` The currently live entries, serialized as a fresh archive with no dead space left by prior `zipFile.addEntry()`/`zipFile.delete()` calls.

The synchronous version of `zipFile.compact()`. Does not modify the open file.

#### `zipFile.delete(name)`#

Added in: v26.8.0

- `name` `<string>`
- Returns: `<Promise>` Fulfilled with `true` if an entry named `name` existed and was removed, `false` otherwise.

Rewrites the central directory without writing any new content - the archive does not grow. Throws `ERR_ZIP_NOT_WRITABLE` if the `ZipFile` was not opened with `{ writable: true }`.

#### `zipFile.deleteSync(name)`#

Added in: v26.8.0

- `name` `<string>`
- Returns: `<boolean>` `true` if an entry named `name` existed and was removed, `false` otherwise.

The synchronous version of `zipFile.delete()`.

#### `zipFile.entries()`#

Added in: v26.8.0

- Returns: `<Iterator>` of `[name, entry]` pairs, where `entry` is a `<Promise>` fulfilled with a `ZipEntry`.

#### `zipFile.entriesSync()`#

Added in: v26.8.0

- Returns: `<Iterator>` of `[name, entry]` pairs, where `entry` is a resolved `ZipEntry` (not a `Promise`).

The synchronous version of `zipFile.entries()`.

#### `zipFile.forEach(callback[, thisArg])`#

Added in: v26.8.0

- `callback` `<Function>`
- `thisArg` `<any>`

#### `zipFile.forEachSync(callback[, thisArg])`#

Added in: v26.8.0

- `callback` `<Function>`
- `thisArg` `<any>`

The synchronous version of `zipFile.forEach()`: `callback` is invoked with a resolved `ZipEntry` instead of a `Promise`.

#### `zipFile.get(name)`#

Added in: v26.8.0

- `name` `<string>`
- Returns: `<Promise>` Fulfilled with a `<ZipEntry>`.

Returns a lazy, file-backed `ZipEntry` for `name`. Nothing is read from disk here and no content is buffered: the returned entry reads (and, for `zipEntry.content()`, decompresses) its member straight from the file on each access, and the `ZipFile` retains no member content. The entry is valid only while this `ZipFile` is open. Reading its content later may throw `ERR_ZIP_ENTRY_TOO_LARGE` if the member is too large to hold in a single buffer; use `zipEntry.contentIterator()` (or `zipFile.stream()`) instead. Throws `ERR_ZIP_ENTRY_NOT_FOUND` if the archive has no entry named `name`.

#### `zipFile.getSync(name)`#

Added in: v26.8.0

- `name` `<string>`
- Returns: `<ZipEntry>`

The synchronous version of `zipFile.get()`. Like `get()`, it reads nothing up front and only builds the lazy handle, so it does not itself block on I/O - but reads performed later through the returned entry (such as `zipEntry.contentSync()`) do; see the note above on synchronous methods.

#### `zipFile.has(name)`#

Added in: v26.8.0

- `name` `<string>`
- Returns: `<boolean>`

#### `zipFile.keys()`#

Added in: v26.8.0

- Returns: `<Iterator>` of entry names.

#### `zipFile.size`#

Added in: v26.8.0

- Type: `<number>`

The number of entries in the archive.

#### `zipFile.stream(name[, options])`#

Added in: v26.8.0

- `name` `<string>`
- `options` `<Object>`
  - `verify` `<boolean>` Verify the entry's CRC-32 checksum. Default: `true`.
  - `maxSize` `<number>` Reject content declaring more than this many uncompressed bytes. Default: no limit.
- Returns: `<Promise>` Fulfilled with a `<stream.Readable>` of the member's decompressed content, without buffering the whole member in memory.

Convenience wrapper that resolves to a `Readable` over `zipEntry.contentIterator()` of `zipFile.get()``(name)`; the compressed bytes are read from disk as the stream is consumed. The returned promise rejects with `ERR_ZIP_ENTRY_NOT_FOUND` if the archive has no entry named `name`.

#### `zipFile.values()`#

Added in: v26.8.0

- Returns: `<Iterator>` of `<Promise>` objects, each fulfilled with a `ZipEntry`.

#### `zipFile.valuesSync()`#

Added in: v26.8.0

- Returns: `<Iterator>` of resolved `ZipEntry` values (not `Promise`s).

The synchronous version of `zipFile.values()`.

#### `zipFile.writable`#

Added in: v26.8.0

- Type: `<boolean>`

Whether this `ZipFile` was opened with `{ writable: true }`.

### Class: `zlib.ZlibBase`#

Added in: v0.5.8
History

Version | Changes
--- | ---
v11.7.0, v10.16.0 | This class was renamed from `Zlib` to `ZlibBase`.

- Extends: `stream.Transform`

Not exported by the `node:zlib` module. It is documented here because it is the base class of the compressor/decompressor classes.

This class inherits from `stream.Transform`, allowing `node:zlib` objects to be used in pipes and similar stream operations.

#### `zlib.bytesWritten`#

Added in: v10.0.0

- Type: `<number>`

The `zlib.bytesWritten` property specifies the number of bytes written to the engine, before the bytes are processed (compressed or decompressed, as appropriate for the derived class).

#### `zlib.close([callback])`#

Added in: v0.9.4

- `callback` `<Function>`

Close the underlying handle.

#### `zlib.flush([kind, ]callback)`#

Added in: v0.5.8

- `kind` Default: `zlib.constants.Z_FULL_FLUSH` for zlib-based streams, `zlib.constants.BROTLI_OPERATION_FLUSH` for Brotli-based streams.
- `callback` `<Function>`

Flush pending data. Don't call this frivolously, premature flushes negatively impact the effectiveness of the compression algorithm.

Calling this only flushes data from the internal `zlib` state, and does not perform flushing of any kind on the streams level. Rather, it behaves like a normal call to `.write()`, i.e. it will be queued up behind other pending writes and will only produce output when data is being read from the stream.

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

Added in: v0.11.4

- `level` `<integer>`
- `strategy` `<integer>`
- `callback` `<Function>`

This function is only available for zlib-based streams, i.e. not Brotli.

Dynamically update the compression level and compression strategy. Only applicable to deflate algorithm.

#### `zlib.reset()`#

Added in: v0.7.0

Reset the compressor/decompressor to factory defaults. Only applicable to the inflate and deflate algorithms.

### Class: `ZstdOptions`#

Added in: v23.8.0, v22.15.0
History

Version | Changes
--- | ---
v26.7.0 | The `dictionary` option can be a `TypedArray`, `DataView`, or `ArrayBuffer`.
v26.5.0 | The `rejectGarbageAfterEnd` option was added.

Stability: 1 - Experimental

Each Zstd-based class takes an `options` object. All options are optional.

- `flush` `<integer>` Default: `zlib.constants.ZSTD_e_continue`
- `finishFlush` `<integer>` Default: `zlib.constants.ZSTD_e_end`
- `chunkSize` `<integer>` Default: `16 * 1024`
- `params` `<Object>` Key-value object containing indexed Zstd parameters.
- `maxOutputLength` `<integer>` Limits output size when using convenience methods. Default: `buffer.kMaxLength`
- `info` `<boolean>` If `true`, returns an object with `buffer` and `engine`. Default: `false`
- `dictionary` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` Optional dictionary used to improve compression efficiency when compressing or decompressing data that shares common patterns with the dictionary.
- `rejectGarbageAfterEnd` `<boolean>` If `true`, decompression fails when input remains after the first complete compressed stream. Default: `false`

For example:

    const stream = zlib.createZstdCompress({
      chunkSize: 32 * 1024,
      params: {
        [zlib.constants.ZSTD_c_compressionLevel]: 10,
        [zlib.constants.ZSTD_c_checksumFlag]: 1,
      },
    });
    js

### Class: `zlib.ZstdCompress`#

Added in: v23.8.0, v22.15.0

Stability: 1 - Experimental

Compress data using the Zstd algorithm.

### Class: `zlib.ZstdDecompress`#

Added in: v23.8.0, v22.15.0

Stability: 1 - Experimental

Decompress data using the Zstd algorithm.

### `zlib.constants`#

Added in: v7.0.0

Provides an object enumerating Zlib-related constants.

### `zlib.crc32(data[, value])`#

Added in: v22.2.0, v20.15.0

- `data` `<string>` | `<Buffer>` | `<TypedArray>` | `<DataView>` When `data` is a string, it will be encoded as UTF-8 before being used for computation.
- `value` `<integer>` An optional starting value. It must be a 32-bit unsigned integer. Default: `0`
- Returns: `<integer>` A 32-bit unsigned integer containing the checksum.

Computes a 32-bit Cyclic Redundancy Check checksum of `data`. If `value` is specified, it is used as the starting value of the checksum, otherwise, 0 is used as the starting value.

The CRC algorithm is designed to compute checksums and to detect error in data transmission. It's not suitable for cryptographic authentication.

To be consistent with other APIs, if the `data` is a string, it will be encoded with UTF-8 before being used for computation. If users only use Node.js to compute and match the checksums, this works well with other APIs that uses the UTF-8 encoding by default.

Some third-party JavaScript libraries compute the checksum on a string based on `str.charCodeAt()` so that it can be run in browsers. If users want to match the checksum computed with this kind of library in the browser, it's better to use the same library in Node.js if it also runs in Node.js. If users have to use `zlib.crc32()` to match the checksum produced by such a third-party library:

1. If the library accepts `Uint8Array` as input, use `TextEncoder` in the browser to encode the string into a `Uint8Array` with UTF-8 encoding, and compute the checksum based on the UTF-8 encoded string in the browser.
2. If the library only takes a string and compute the data based on `str.charCodeAt()`, on the Node.js side, convert the string into a buffer using `Buffer.from(str, 'utf16le')`.

    import zlib from 'node:zlib';
    import { Buffer } from 'node:buffer';

    let crc = zlib.crc32('hello');  // 907060870
    crc = zlib.crc32('world', crc);  // 4192936109

    crc = zlib.crc32(Buffer.from('hello', 'utf16le'));  // 1427272415
    crc = zlib.crc32(Buffer.from('world', 'utf16le'), crc);  // 4150509955
    const zlib = require('node:zlib');
    const { Buffer } = require('node:buffer');

    let crc = zlib.crc32('hello');  // 907060870
    crc = zlib.crc32('world', crc);  // 4192936109

    crc = zlib.crc32(Buffer.from('hello', 'utf16le'));  // 1427272415
    crc = zlib.crc32(Buffer.from('world', 'utf16le'), crc);  // 4150509955
    javascript

### `zlib.createBrotliCompress([options])`#

Added in: v11.7.0, v10.16.0

- `options` `<brotli options>`

Creates and returns a new `BrotliCompress` object.

### `zlib.createBrotliDecompress([options])`#

Added in: v11.7.0, v10.16.0

- `options` `<brotli options>`

Creates and returns a new `BrotliDecompress` object.

### `zlib.createDeflate([options])`#

Added in: v0.5.8

- `options` `<zlib options>`

Creates and returns a new `Deflate` object.

### `zlib.createDeflateRaw([options])`#

Added in: v0.5.8

- `options` `<zlib options>`

Creates and returns a new `DeflateRaw` object.

An upgrade of zlib from 1.2.8 to 1.2.11 changed behavior when `windowBits` is set to 8 for raw deflate streams. zlib would automatically set `windowBits` to 9 if was initially set to 8. Newer versions of zlib will throw an exception, so Node.js restored the original behavior of upgrading a value of 8 to 9, since passing `windowBits = 9` to zlib actually results in a compressed stream that effectively uses an 8-bit window only.

### `zlib.createGunzip([options])`#

Added in: v0.5.8

- `options` `<zlib options>`

Creates and returns a new `Gunzip` object.

### `zlib.createGzip([options])`#

Added in: v0.5.8

- `options` `<zlib options>`

Creates and returns a new `Gzip` object. See example.

### `zlib.createInflate([options])`#

Added in: v0.5.8

- `options` `<zlib options>`

Creates and returns a new `Inflate` object.

### `zlib.createInflateRaw([options])`#

Added in: v0.5.8

- `options` `<zlib options>`

Creates and returns a new `InflateRaw` object.

### `zlib.createUnzip([options])`#

Added in: v0.5.8

- `options` `<zlib options>`

Creates and returns a new `Unzip` object.

### `zlib.createZipArchive(entries[, options])`#

Added in: v26.8.0

Stability: 1.0 - Early development

The ZIP archive API is experimental. Using any part of it (this function among them) emits an experimental warning the first time; merely importing `node:zlib` does not.

- `entries` `<Iterable>` | `<AsyncIterable>` of `ZipEntry`.
- `options` `<string>` | `<Object>` An archive comment, as a shorthand for `{ comment: options }`.
  - `comment` `<string>` An archive comment.
  - `baseOffset` `<number>` Shifts every local/central header offset the archive records by this many bytes, so the emitted stream is self-describing even when something else is written before it - for example, appending the archive after `baseOffset` bytes already written to the same file, rather than at its start. Default: `0`.
- Returns: `<stream.Readable>` A byte stream of the serialized archive.

Serializes `entries` into a ZIP archive, switching to Zip64 structures automatically once the entry count, or any offset or size, exceeds what the classic 32-/16-bit ZIP fields can hold. The returned `Readable` is also an `AsyncIterable` of the same `<Buffer>` chunks it streams.

Entries are written in iteration order and nothing deduplicates names: an iterable that yields two entries with the same name produces an archive containing both, and most extraction tools keep the one that appears later. `ZipBuffer` and `ZipFile` `add()` methods replace entries by name instead.

The entries are owned by the returned stream: each is consumed as the archive is produced and must not be reused afterwards. This matters for streaming entries (from `zlib.ZipEntry.createStream()`), which hold an underlying source such as a file read stream. If the returned stream is destroyed before it is fully consumed - for example, the destination of a `pipeline()` fails - it disposes the entry it was serializing and every entry still queued behind it, destroying their sources so no descriptor leaks. Consume the stream to the end, or destroy it (directly, through a failed `pipeline()`, or with `await using`), to guarantee this cleanup; a stream that is neither consumed nor destroyed cannot release anything. A `ZipEntry` that is never handed to an archive can be released directly with `Symbol.dispose` / `Symbol.asyncDispose`.

Throws an `ERR_ZIP_ARCHIVE_TOO_LARGE` error if the archive comment exceeds 65,535 bytes when encoded as UTF-8.

    import { createWriteStream } from 'node:fs';
    import { pipeline } from 'node:stream/promises';
    import { Buffer } from 'node:buffer';
    import { ZipEntry, createZipArchive } from 'node:zlib';

    const entries = [
      await ZipEntry.create('hello.txt', Buffer.from('Hello, world!')),
      await ZipEntry.create('data/', Buffer.alloc(0)),
    ];
    await pipeline(
      createZipArchive(entries, 'created by node:zlib'),
      createWriteStream('archive.zip'),
    );
    const { createWriteStream } = require('node:fs');
    const { pipeline } = require('node:stream/promises');
    const { ZipEntry, createZipArchive } = require('node:zlib');

    async function main() {
      const entries = [
        await ZipEntry.create('hello.txt', Buffer.from('Hello, world!')),
        await ZipEntry.create('data/', Buffer.alloc(0)),
      ];
      await pipeline(
        createZipArchive(entries, 'created by node:zlib'),
        createWriteStream('archive.zip'),
      );
    }
    main();
    javascript

Passing `options.baseOffset` produces an archive that is valid immediately when placed after other content in the same file, without relying on a reader's self-extracting-archive detection to compensate for the shift:

    import { createWriteStream } from 'node:fs';
    import { Buffer } from 'node:buffer';
    import { ZipEntry, createZipArchive } from 'node:zlib';

    const prefix = Buffer.from('#!/bin/sh\nexit 0\n');
    const entries = [await ZipEntry.create('hello.txt', Buffer.from('Hello, world!'))];
    const out = createWriteStream('self-extracting.zip');
    out.write(prefix);
    createZipArchive(entries, { baseOffset: prefix.byteLength }).pipe(out);
    mjs

### `zlib.createZipArchiveSync(entries[, options])`#

Added in: v26.8.0

Stability: 1.0 - Early development

The ZIP archive API is experimental. Using any part of it (this function among them) emits an experimental warning the first time; merely importing `node:zlib` does not.

- `entries` `<Iterable>` of `ZipEntry`.
- `options` `<string>` | `<Object>` See `zlib.createZipArchive()`.
- Returns: `<Iterator>` of `<Buffer>` chunks making up the serialized archive.

The synchronous version of `zlib.createZipArchive()`. Blocks the Node.js event loop and further JavaScript execution until the whole archive (including any deflate passes) has been produced; use only where synchronous execution is appropriate (for example, short-lived scripts or startup code), not in code that must stay responsive. `entries` must be a plain (synchronous) `Iterable` - a streaming entry created with `zlib.ZipEntry.createStream()` throws when its turn to serialize comes up, since draining its asynchronous source has no synchronous equivalent.

As with `zlib.createZipArchive()`, the entries are owned by the returned iterator and must not be reused. If iteration stops early - including the throw on a streaming entry - the entry that stopped it and every entry still queued behind it are disposed, releasing any sources they hold.

### `zlib.zipFiles(files[, options])`#

Added in: v26.8.0

Stability: 1.0 - Early development

The ZIP archive API is experimental. Using any part of it (this function among them) emits an experimental warning the first time; merely importing `node:zlib` does not.

- `files` `<Iterable>` of `[sourcePath, entryName]` string pairs. Any iterable works — an array, a `Map`, the result of `Object.entries()`, a generator.
- `options` `<string>` | `<Object>`
  - `followSymlinks` `<boolean>` Resolve a symbolic link and archive the file it points to, rather than storing the link itself. Default: `true`.
  - `comment` `<string>` An archive comment; a string `options` is shorthand for `{ comment: options }`.
  - `baseOffset` `<number>` See `zlib.createZipArchive()`.
- Returns: `<stream.Readable>` of `<Buffer>` chunks making up the serialized archive.

Builds an archive from files on disk. For each `[sourcePath, entryName]` pair it reads `sourcePath` and adds an entry named `entryName`, capturing the file's Unix mode and modification time. A directory becomes a directory entry; a regular file's contents are streamed in (as a `zlib.ZipEntry.createStream()` entry) without being buffered in memory. Directory contents are not walked recursively — list each path you want included.

When `followSymlinks` is `true` (the default) a symbolic link is resolved and archived as its target file; when it is `false` the link itself is stored as a symbolic-link entry whose content is the target path (see `zlib.ZipEntry.createSymlink()`).

    import { zipFiles } from 'node:zlib';
    import { createWriteStream } from 'node:fs';
    import { pipeline } from 'node:stream/promises';

    await pipeline(
      zipFiles([
        ['/data/report.pdf', 'report.pdf'],
        ['/data/notes.txt', 'docs/notes.txt'],
      ]),
      createWriteStream('archive.zip'),
    );
    mjs

### `zlib.createZstdCompress([options])`#

Added in: v23.8.0, v22.15.0

Stability: 1 - Experimental

- `options` `<zstd options>`

Creates and returns a new `ZstdCompress` object.

### `zlib.createZstdDecompress([options])`#

Added in: v23.8.0, v22.15.0

Stability: 1 - Experimental

- `options` `<zstd options>`

Creates and returns a new `ZstdDecompress` object.

### `zlib.getMaxZipContentSize()`#

Added in: v26.8.0

Stability: 1.0 - Early development

The ZIP archive API is experimental. Using any part of it (this function among them) emits an experimental warning the first time; merely importing `node:zlib` does not.

- Returns: `<number>`

The current default ceiling, in bytes, applied by `zipEntry.content()` when no explicit `maxSize` is given. Default: `268435456` (256 MiB).

### `zlib.setMaxZipContentSize(size)`#

Added in: v26.8.0

Stability: 1.0 - Early development

The ZIP archive API is experimental. Using any part of it (this function among them) emits an experimental warning the first time; merely importing `node:zlib` does not.

- `size` `<number>`

Sets the default ceiling used by `zipEntry.content()` when no explicit `maxSize` option is given. This is a guard against zip bombs: an archive whose central directory declares a member larger than this is rejected before allocating memory for it. Streaming reads (`zipEntry.contentIterator()`, `zipFile.stream()`) are bounded-memory by design and are not affected by this setting.

### Convenience methods#

All of these take a `<Buffer>`, `<TypedArray>`, `<DataView>`, `<ArrayBuffer>`, or string as the first argument, an optional second argument to supply options to the `zlib` classes and will call the supplied callback with `callback(error, result)`.

Every method has a `*Sync` counterpart, which accept the same arguments, but without a callback.

#### `zlib.brotliCompress(buffer[, options], callback)`#

Added in: v11.7.0, v10.16.0

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<brotli options>`
- `callback` `<Function>`

#### `zlib.brotliCompressSync(buffer[, options])`#

Added in: v11.7.0, v10.16.0

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<brotli options>`

Compress a chunk of data with `BrotliCompress`.

#### `zlib.brotliDecompress(buffer[, options], callback)`#

Added in: v11.7.0, v10.16.0

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<brotli options>`
- `callback` `<Function>`

#### `zlib.brotliDecompressSync(buffer[, options])`#

Added in: v11.7.0, v10.16.0

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<brotli options>`

Decompress a chunk of data with `BrotliDecompress`.

#### `zlib.deflate(buffer[, options], callback)`#

Added in: v0.6.0
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`
- `callback` `<Function>`

#### `zlib.deflateSync(buffer[, options])`#

Added in: v0.11.12
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`

Compress a chunk of data with `Deflate`.

#### `zlib.deflateRaw(buffer[, options], callback)`#

Added in: v0.6.0
History

Version | Changes
--- | ---
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`
- `callback` `<Function>`

#### `zlib.deflateRawSync(buffer[, options])`#

Added in: v0.11.12
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`

Compress a chunk of data with `DeflateRaw`.

#### `zlib.gunzip(buffer[, options], callback)`#

Added in: v0.6.0
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`
- `callback` `<Function>`

#### `zlib.gunzipSync(buffer[, options])`#

Added in: v0.11.12
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`

Decompress a chunk of data with `Gunzip`.

#### `zlib.gzip(buffer[, options], callback)`#

Added in: v0.6.0
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`
- `callback` `<Function>`

#### `zlib.gzipSync(buffer[, options])`#

Added in: v0.11.12
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`

Compress a chunk of data with `Gzip`.

#### `zlib.inflate(buffer[, options], callback)`#

Added in: v0.6.0
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`
- `callback` `<Function>`

#### `zlib.inflateSync(buffer[, options])`#

Added in: v0.11.12
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`

Decompress a chunk of data with `Inflate`.

#### `zlib.inflateRaw(buffer[, options], callback)`#

Added in: v0.6.0
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`
- `callback` `<Function>`

#### `zlib.inflateRawSync(buffer[, options])`#

Added in: v0.11.12
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`

Decompress a chunk of data with `InflateRaw`.

#### `zlib.unzip(buffer[, options], callback)`#

Added in: v0.6.0
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`
- `callback` `<Function>`

#### `zlib.unzipSync(buffer[, options])`#

Added in: v0.11.12
History

Version | Changes
--- | ---
v9.4.0 | The `buffer` parameter can be an `ArrayBuffer`.
v8.0.0 | The `buffer` parameter can be any `TypedArray` or `DataView`.
v8.0.0 | The `buffer` parameter can be an `Uint8Array` now.

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zlib options>`

Decompress a chunk of data with `Unzip`.

#### `zlib.zstdCompress(buffer[, options], callback)`#

Added in: v23.8.0, v22.15.0

Stability: 1 - Experimental

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zstd options>`
- `callback` `<Function>`

#### `zlib.zstdCompressSync(buffer[, options])`#

Added in: v23.8.0, v22.15.0

Stability: 1 - Experimental

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zstd options>`

Compress a chunk of data with `ZstdCompress`.

#### `zlib.zstdDecompress(buffer[, options], callback)`#

Added in: v23.8.0, v22.15.0

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zstd options>`
- `callback` `<Function>`

#### `zlib.zstdDecompressSync(buffer[, options])`#

Added in: v23.8.0, v22.15.0

Stability: 1 - Experimental

- `buffer` `<Buffer>` | `<TypedArray>` | `<DataView>` | `<ArrayBuffer>` | `<string>`
- `options` `<zstd options>`

Decompress a chunk of data with `ZstdDecompress`.

### Iterable Compression#

Added in: v25.9.0

Stability: 1 - Experimental

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);
    javascript

    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'
    javascript

#### `compressBrotli([options])`#

#### `compressBrotliSync([options])`#

Added in: v25.9.0

- `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])`#

Added in: v25.9.0

- `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])`#

Added in: v25.9.0

- `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])`#

Added in: v25.9.0

- `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 as a non-negative safe integer (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])`#

Added in: v25.9.0

- `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])`#

Added in: v25.9.0

- `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])`#

Added in: v25.9.0

- `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])`#

Added in: v25.9.0

- `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.