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.