nodejs/doc/api/zlib.markdown

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.

• chunkSize (default: 16*1024)
• windowBits
• level (compression only)
• memLevel (compression only)
• strategy (compression only)

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.