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Implements thepermessage-deflateWebSocket protocol extension as a plugin forwebsocket-extensions.

$ npm install permessage-deflate2

Add the plugin to your extensions:

varExtensions=require('websocket-extensions'),deflate=require('permessage-deflate');varexts=newExtensions();exts.add(deflate);

The extension can be configured, for example:

varExtensions=require('websocket-extensions'),deflate=require('permessage-deflate'),zlib=require('zlib');deflate=deflate.configure({level:zlib.Z_BEST_COMPRESSION,maxWindowBits:13,threshold:100// optional, defaults to 0 (always compress)});varexts=newExtensions();exts.add(deflate);

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

• threshold: sets the minimum size of messages to be compressed, defaults to 0
• level: sets the compression level, can be an integer from0 to9, or oneof the constantszlib.Z_NO_COMPRESSION,zlib.Z_BEST_SPEED,zlib.Z_BEST_COMPRESSION, orzlib.Z_DEFAULT_COMPRESSION
• memLevel: sets how much memory the compressor allocates, can be an integerfrom1 to9, or one of the constantszlib.Z_MIN_MEMLEVEL,zlib.Z_MAX_MEMLEVEL, orzlib.Z_DEFAULT_MEMLEVEL
• strategy: can be one of the constantszlib.Z_FILTERED,zlib.Z_HUFFMAN_ONLY,zlib.Z_RLE,zlib.Z_FIXED, orzlib.Z_DEFAULT_STRATEGY

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

• noContextTakeover: iftrue, stops the session reusing a deflate contextbetween messages
• requestNoContextTakeover: iftrue, makes the session tell the other peernot to reuse a deflate context between messages
• maxWindowBits: an integer from8 to15 inclusive that sets the maximumsize of the session's sliding window; a lower window size will be used ifrequested by the peer
• requestMaxWindowBits: an integer from8 to15 inclusive to ask the otherpeer to use to set its maximum sliding window size, if supported