Node.js v0.5.9 Manual & Documentation


Table Of Contents


Zlib

You can access this module with:

var zlib = require('zlib');
var gzip = zlib.createGzip();
var fs = require('fs');
var inp = fs.createReadStream('input.txt');
var out = fs.createWriteStream('input.txt.gz');

inp.pipe(gzip).pipe(out);

This provides bindings to Gzip/Gunzip, Deflate/Inflate, and DeflateRaw/InflateRaw classes. Each class takes the same options, and is a readable/writable Stream.

Constants

All of the constants defined in zlib.h are also defined on require('zlib'). They are described in more detail in the zlib documentation. See http://zlib.net/manual.html#Constants for more details.

zlib.Gzip

Compress data using gzip.

zlib.Gunzip

Decompress a gzip stream.

zlib.Deflate

Compress data using deflate.

zlib.Inflate

Decompress a deflate stream.

zlib.DeflateRaw

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

zlib.InflateRaw

Decompress a raw deflate stream.

zlib.Unzip

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

Options

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

Note that some options are only relevant when compressing, and are ignored by the decompression classes.

See the description of deflateInit2 and inflateInit2 at http://zlib.net/manual.html#Advanced for more information on these.

Memory Usage Tuning

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

The memory requirements for deflate are (in bytes):

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

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

For example, if you want to reduce the default memory requirements from 256K to 128K, set the options to:

{ windowBits: 14, memLevel: 7 }

Of course this will generally degrade compression (there's no free lunch).

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.