LZ4

LZ4 is a very fast compression and decompression algorithm. This nodejs module provides a Javascript implementation of the decoder as well as native bindings to the LZ4 functions. Nodejs Streams are also supported for compression and decompression.

NB. Version 0.2 does not support the legacy format, only the one as of "LZ4 Streaming Format 1.4". Use version 0.1 if required.

Install

With NodeJS:

npm install lz4

Within the browser, using build/lz4.js:

<script type="text/javascript" src="/path/to/lz4.js"></script>
<script type="text/javascript">
// Nodejs-like Buffer built-in
var Buffer = require('buffer').Buffer
var LZ4 = require('lz4')

// Some data to be compressed
var data = 'Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.'
data += data
// LZ4 can only work on Buffers
var input = new Buffer(data)
// Initialize the output buffer to its maximum length based on the input data
var output = new Buffer( LZ4.encodeBound(input.length) )

// block compression (no archive format)
var compressedSize = LZ4.encodeBlock(input, output)
// remove unnecessary bytes
output = output.slice(0, compressedSize)

console.log( "compressed data", output.slice(0, compressedSize) )

// block decompression (no archive format)
var uncompressed = new Buffer(input.length)
var uncompressedSize = LZ4.decodeBlock(output, uncompressed)
uncompressed = uncompressed.slice(0, uncompressedSize)

console.log( "uncompressed data", uncompressed )
</script>

See below for more LZ4 functions.

Usage

Encoding

There are 2 ways to encode:

• asynchronous using nodejs Streams - slowest but can handle very large data sets (no memory limitations).
• synchronous by feeding the whole set of data - faster but is limited by the amount of memory

Asynchronous encoding

First, create an LZ4 encoding NodeJS stream with LZ4#createEncoderStream(options).

• options (Object): LZ4 stream options (optional)
  • options.blockMaxSize (Number): chunk size to use (default=4Mb)
  • options.highCompression (Boolean): use high compression (default=false)
  • options.blockIndependence (Boolean): (default=true)
  • options.blockChecksum (Boolean): add compressed blocks checksum (default=false)
  • options.streamSize (Boolean): add full LZ4 stream size (default=false)
  • options.streamChecksum (Boolean): add full LZ4 stream checksum (default=true)
  • options.dict (Boolean): use dictionary (default=false)
  • options.dictId (Integer): dictionary id (default=0)

The stream can then encode any data piped to it. It will emit a data event on each encoded chunk, which can be saved into an output stream.

The following example shows how to encode a file test into test.lz4.

var fs = require('fs')
var lz4 = require('lz4')

var encoder = lz4.createEncoderStream()

var input = fs.createReadStream('test')
var output = fs.createWriteStream('test.lz4')

input.pipe(encoder).pipe(output)

Synchronous encoding

Read the data into memory and feed it to LZ4#encode(input[, options]) to decode an LZ4 stream.

• input (Buffer): data to encode
• options (Object): LZ4 stream options (optional)
  • options.blockMaxSize (Number): chunk size to use (default=4Mb)
  • options.highCompression (Boolean): use high compression (default=false)
  • options.blockIndependence (Boolean): (default=true)
  • options.blockChecksum (Boolean): add compressed blocks checksum (default=false)
  • options.streamSize (Boolean): add full LZ4 stream size (default=false)
  • options.streamChecksum (Boolean): add full LZ4 stream checksum (default=true)
  • options.dict (Boolean): use dictionary (default=false)
  • options.dictId (Integer): dictionary id (default=0)

var fs = require('fs')
var lz4 = require('lz4')

var input = fs.readFileSync('test')
var output = lz4.encode(input)

fs.writeFileSync('test.lz4', output)

Decoding

There are 2 ways to decode:

• asynchronous using nodejs Streams - slowest but can handle very large data sets (no memory limitations)
• synchronous by feeding the whole LZ4 data - faster but is limited by the amount of memory

Asynchronous decoding

First, create an LZ4 decoding NodeJS stream with LZ4#createDecoderStream().

The stream can then decode any data piped to it. It will emit a data event on each decoded sequence, which can be saved into an output stream.

The following example shows how to decode an LZ4 compressed file test.lz4 into test.

var fs = require('fs')
var lz4 = require('lz4')

var decoder = lz4.createDecoderStream()

var input = fs.createReadStream('test.lz4')
var output = fs.createWriteStream('test')

input.pipe(decoder).pipe(output)

Synchronous decoding

Read the data into memory and feed it to LZ4#decode(input) to produce an LZ4 stream.

• input (Buffer): data to decode

var fs = require('fs')
var lz4 = require('lz4')

var input = fs.readFileSync('test.lz4')
var output = lz4.decode(input)

fs.writeFileSync('test', output)

Block level encoding/decoding

In some cases, it is useful to be able to manipulate an LZ4 block instead of an LZ4 stream. The functions to decode and encode are therefore exposed as:

• LZ4#decodeBlock(input, output) (Number) >=0: uncompressed size, <0: error at offset
  • input (Buffer): data block to decode
  • output (Buffer): decoded data block
• LZ4#encodeBound(inputSize) (Number): maximum size for a compressed block
  • inputSize (Number) size of the input, 0 if too large This is required to size the buffer for a block encoded data
• LZ4#encodeBlock(input, output) (Number) >0: compressed size, =0: not compressible
  • input (Buffer): data block to encode
  • output (Buffer): encoded data block
• LZ4#encodeBlockHC(input, output) (Number) >0: compressed size, =0: not compressible
  • input (Buffer): data block to encode with high compression
  • output (Buffer): encoded data block

Blocks do not have any magic number and are provided as is. It is useful to store somewhere the size of the original input for decoding. LZ4#encodeBlockHC() is not available as pure Javascript.

How it works

• LZ4 stream format

Restrictions / Issues

• blockIndependence property only supported for true

License

MIT