permessage-deflate 

Implements the
permessage-deflate
WebSocket protocol extension as a plugin for
websocket-extensions.

Installation

``
$ npm install permessage-deflate
`

Usage

Add the plugin to your extensions:

`js
var Extensions = require('websocket-extensions'),
deflate = require('permessage-deflate');

var exts = new Extensions();
exts.add(deflate);
`

The extension can be configured, for example:

`js
var Extensions = require('websocket-extensions'),
deflate = require('permessage-deflate'),
zlib = require('zlib');

deflate = deflate.configure({
level: zlib.Z_BEST_COMPRESSION,
maxWindowBits: 13
});

var exts = new Extensions();
exts.add(deflate);
`

The set of available options can be split into two sets: those that control the
session's compressor for outgoing messages and do not need to be communicated to
the peer, and those that are negotiated as part of the protocol. The settings
only affecting the compressor are described fully in the zlib
documentation:

- level: sets the compression level, can be an integer from 0 to 9, or one
of the constants zlib.Z_NO_COMPRESSION, zlib.Z_BEST_SPEED,
zlib.Z_BEST_COMPRESSION, or zlib.Z_DEFAULT_COMPRESSION
- memLevel: sets how much memory the compressor allocates, can be an integer
from 1 to 9, or one of the constants zlib.Z_MIN_MEMLEVEL,
zlib.Z_MAX_MEMLEVEL, or zlib.Z_DEFAULT_MEMLEVEL
- strategy: can be one of the constants zlib.Z_FILTERED,
zlib.Z_HUFFMAN_ONLY, zlib.Z_RLE, zlib.Z_FIXED, or
zlib.Z_DEFAULT_STRATEGY

The other options relate to settings that are negotiated via the protocol and
can be used to set the local session's behaviour and control that of the peer:

- noContextTakeover: if true, stops the session reusing a deflate context
between messages
- requestNoContextTakeover: if true, makes the session tell the other peer
not to reuse a deflate context between messages
- maxWindowBits: an integer from 8 to 15 inclusive that sets the maximum
size of the session's sliding window; a lower window size will be used if
requested by the peer
- requestMaxWindowBits: an integer from 8 to 15` inclusive to ask the other
peer to use to set its maximum sliding window size, if supported