compression

Node.js compression middleware.

Install

$ npm install compression

API

var compression = require('compression')

compression(options)

Returns the compression middleware using the given options.

app.use(compression({
  threshold: 512
}))

Options

compression() accepts these properties in the options object. In addition to those listed below, zlib options may be passed in to the options object.

filter

A function to decide if the response should be considered for compression. This function is called as filter(req, res) and is expected to return true to consider the response for compression, or false to not compress the response.

The default filter function uses the compressible module to determine if res.getHeader('Content-Type') is compressible.

threshold

The byte threshold for the response body size before compression is considered for the response, defaults to 1kb. This is a number of bytes, any string accepted by the bytes module, or false.

.filter

The default filter function. This is used to construct a custom filter function that is an extension of the default function.

app.use(compression({filter: shouldCompress}))

function shouldCompress(req, res) {
  if (req.headers['x-no-compression']) {
    // don't compress responses with this request header
    return false
  }

  // fallback to standard filter function
  return compression.filter(req, res)
}

res.flush

This module adds a res.flush() method to force the partially-compressed response to be flushed to the client.

Examples

express/connect

When using this module with express or connect, simply app.use the module as high as you like. Requests that pass through the middleware will be compressed.

var compression = require('compression')
var express = require('express')

var app = express()

// compress all requests
app.use(compression())

// add alll routes

Server-Sent Events

Because of the nature of compression this module does not work out of the box with server-sent events. To compress content, a window of the output needs to be buffered up in order to get good compression. Typically when using server-sent events, there are certain block of data that need to reach the client.

You can achieve this by calling res.flush() when you need the data written to actually make it to the client.

var compression = require('compression')
var express     = require('express')

var app = express()

// compress responses
app.use(compression())

// server-sent event stream
app.get('/events', function (req, res) {
  res.setHeader('Content-Type', 'text/event-stream')
  res.setHeader('Cache-Control', 'no-cache')

  // send a ping approx every 2 seconds
  var timer = setInterval(function () {
    res.write('data: ping\n\n')

    // !!! this is the important part
    res.flush()
  }, 2000)

  res.on('close', function () {
    clearInterval(timer)
  })
})

License

MIT