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/*!
* compression
* Copyright(c) 2010 Sencha Inc.
* Copyright(c) 2011 TJ Holowaychuk
* Copyright(c) 2014 Jonathan Ong
* Copyright(c) 2014-2015 Douglas Christopher Wilson
* MIT Licensed
*/
'use strict'
/**
* Module dependencies.
* @private
*/
var accepts = require('accepts')
var Buffer = require('safe-buffer').Buffer
var bytes = require('bytes')
var compressible = require('compressible')
var debug = require('debug')('compression')
var onHeaders = require('on-headers')
var vary = require('vary')
var zlib = require('zlib')
/**
* Module exports.
*/
module.exports = compression
module.exports.filter = shouldCompress
/**
* Module variables.
* @private
*/
var cacheControlNoTransformRegExp = /(?:^|,)\s*?no-transform\s*?(?:,|$)/
/**
* Compress response data with gzip / deflate.
*
* @param {Object} [options]
* @return {Function} middleware
* @public
*/
function compression (options) {
var opts = options || {}
// options
var filter = opts.filter || shouldCompress
var threshold = bytes.parse(opts.threshold)
if (threshold == null) {
threshold = 1024
}
return function compression (req, res, next) {
var ended = false
var length
var listeners = []
var stream
var _end = res.end
var _on = res.on
var _write = res.write
// flush
res.flush = function flush () {
if (stream) {
stream.flush()
}
}
// proxy
res.write = function write (chunk, encoding) {
if (ended) {
return false
}
if (!this._header) {
this._implicitHeader()
}
return stream
? stream.write(toBuffer(chunk, encoding))
: _write.call(this, chunk, encoding)
}
res.end = function end (chunk, encoding) {
if (ended) {
return false
}
if (!this._header) {
// estimate the length
if (!this.getHeader('Content-Length')) {
length = chunkLength(chunk, encoding)
}
this._implicitHeader()
}
if (!stream) {
return _end.call(this, chunk, encoding)
}
// mark ended
ended = true
// write Buffer for Node.js 0.8
return chunk
? stream.end(toBuffer(chunk, encoding))
: stream.end()
}
res.on = function on (type, listener) {
if (!listeners || type !== 'drain') {
return _on.call(this, type, listener)
}
if (stream) {
return stream.on(type, listener)
}
// buffer listeners for future stream
listeners.push([type, listener])
return this
}
function nocompress (msg) {
debug('no compression: %s', msg)
addListeners(res, _on, listeners)
listeners = null
}
onHeaders(res, function onResponseHeaders () {
// determine if request is filtered
if (!filter(req, res)) {
nocompress('filtered')
return
}
// determine if the entity should be transformed
if (!shouldTransform(req, res)) {
nocompress('no transform')
return
}
// vary
vary(res, 'Accept-Encoding')
// content-length below threshold
if (Number(res.getHeader('Content-Length')) < threshold || length < threshold) {
nocompress('size below threshold')
return
}
var encoding = res.getHeader('Content-Encoding') || 'identity'
// already encoded
if (encoding !== 'identity') {
nocompress('already encoded')
return
}
// head
if (req.method === 'HEAD') {
nocompress('HEAD request')
return
}
// compression method
var accept = accepts(req)
var method = accept.encoding(['gzip', 'deflate', 'identity'])
// we really don't prefer deflate
if (method === 'deflate' && accept.encoding(['gzip'])) {
method = accept.encoding(['gzip', 'identity'])
}
// negotiation failed
if (!method || method === 'identity') {
nocompress('not acceptable')
return
}
// compression stream
debug('%s compression', method)
stream = method === 'gzip'
? zlib.createGzip(opts)
: zlib.createDeflate(opts)
// add buffered listeners to stream
addListeners(stream, stream.on, listeners)
// header fields
res.setHeader('Content-Encoding', method)
res.removeHeader('Content-Length')
// compression
stream.on('data', function onStreamData (chunk) {
if (_write.call(res, chunk) === false) {
stream.pause()
}
})
stream.on('end', function onStreamEnd () {
_end.call(res)
})
_on.call(res, 'drain', function onResponseDrain () {
stream.resume()
})
})
next()
}
}
/**
* Add bufferred listeners to stream
* @private
*/
function addListeners (stream, on, listeners) {
for (var i = 0; i < listeners.length; i++) {
on.apply(stream, listeners[i])
}
}
/**
* Get the length of a given chunk
*/
function chunkLength (chunk, encoding) {
if (!chunk) {
return 0
}
return !Buffer.isBuffer(chunk)
? Buffer.byteLength(chunk, encoding)
: chunk.length
}
/**
* Default filter function.
* @private
*/
function shouldCompress (req, res) {
var type = res.getHeader('Content-Type')
if (type === undefined || !compressible(type)) {
debug('%s not compressible', type)
return false
}
return true
}
/**
* Determine if the entity should be transformed.
* @private
*/
function shouldTransform (req, res) {
var cacheControl = res.getHeader('Cache-Control')
// Don't compress for Cache-Control: no-transform
// https://tools.ietf.org/html/rfc7234#section-5.2.2.4
return !cacheControl ||
!cacheControlNoTransformRegExp.test(cacheControl)
}
/**
* Coerce arguments to Buffer
* @private
*/
function toBuffer (chunk, encoding) {
return !Buffer.isBuffer(chunk)
? Buffer.from(chunk, encoding)
: chunk
}