http-gzip-maybe 
Compress an HTTP response if the client has headers that allow it
Usage
var gzipMaybe = require('http-gzip-maybe')
var http = require('http')
var pump = require('pump')
http.createServer(function (req, res) {
var gzip = gzipMaybe(req, res)
pump(req, gzip, res)
}).listen(8080)API
stream = gzipMaybe(req, res)
Create a transform stream that conditionally compresses the outgoing data.