node_modules/compression/README.md - nifi-fds - Git at Google

 # compression

 [![NPM Version][npm-image]][npm-url]
 [![NPM Downloads][downloads-image]][downloads-url]
 [![Build Status][travis-image]][travis-url]
 [![Test Coverage][coveralls-image]][coveralls-url]

 Node.js compression middleware.

 The following compression codings are supported:

   - deflate
   - gzip

 ## Install

 This is a [Node.js](https://nodejs.org/en/) module available through the
 [npm registry](https://www.npmjs.com/). Installation is done using the
 [`npm install` command](https://docs.npmjs.com/getting-started/installing-npm-packages-locally):

 ```bash
 $ npm install compression
 ```

 ## API

 <!-- eslint-disable no-unused-vars -->

 ```js
 var compression = require('compression')
 ```

 ### compression([options])

 Returns the compression middleware using the given `options`. The middleware
 will attempt to compress response bodies for all request that traverse through
 the middleware, based on the given `options`.

 This middleware will never compress responses that include a `Cache-Control`
 header with the [`no-transform` directive](https://tools.ietf.org/html/rfc7234#section-5.2.2.4),
 as compressing will transform the body.

 #### Options

 `compression()` accepts these properties in the options object. In addition to
 those listed below, [zlib](http://nodejs.org/api/zlib.html) options may be
 passed in to the options object.

 ##### chunkSize

 The default value is `zlib.Z_DEFAULT_CHUNK`, or `16384`.

 See [Node.js documentation](http://nodejs.org/api/zlib.html#zlib_memory_usage_tuning)
 regarding the usage.

 ##### 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](https://www.npmjs.com/package/compressible)
 module to determine if `res.getHeader('Content-Type')` is compressible.

 ##### level

 The level of zlib compression to apply to responses. A higher level will result
 in better compression, but will take longer to complete. A lower level will
 result in less compression, but will be much faster.

 This is an integer in the range of `0` (no compression) to `9` (maximum
 compression). The special value `-1` can be used to mean the "default
 compression level", which is a default compromise between speed and
 compression (currently equivalent to level 6).

   - `-1` Default compression level (also `zlib.Z_DEFAULT_COMPRESSION`).
   - `0` No compression (also `zlib.Z_NO_COMPRESSION`).
   - `1` Fastest compression (also `zlib.Z_BEST_SPEED`).
   - `2`
   - `3`
   - `4`
   - `5`
   - `6` (currently what `zlib.Z_DEFAULT_COMPRESSION` points to).
   - `7`
   - `8`
   - `9` Best compression (also `zlib.Z_BEST_COMPRESSION`).

 The default value is `zlib.Z_DEFAULT_COMPRESSION`, or `-1`.

 **Note** in the list above, `zlib` is from `zlib = require('zlib')`.

 ##### memLevel

 This specifies how much memory should be allocated for the internal compression
 state and is an integer in the range of `1` (minimum level) and `9` (maximum
 level).

 The default value is `zlib.Z_DEFAULT_MEMLEVEL`, or `8`.

 See [Node.js documentation](http://nodejs.org/api/zlib.html#zlib_memory_usage_tuning)
 regarding the usage.

 ##### strategy

 This is used to tune the compression algorithm. This value only affects the
 compression ratio, not the correctness of the compressed output, even if it
 is not set appropriately.

   - `zlib.Z_DEFAULT_STRATEGY` Use for normal data.
   - `zlib.Z_FILTERED` Use for data produced by a filter (or predictor).
     Filtered data consists mostly of small values with a somewhat random
     distribution. In this case, the compression algorithm is tuned to
     compress them better. The effect is to force more Huffman coding and less
     string matching; it is somewhat intermediate between `zlib.Z_DEFAULT_STRATEGY`
     and `zlib.Z_HUFFMAN_ONLY`.
   - `zlib.Z_FIXED` Use to prevent the use of dynamic Huffman codes, allowing
     for a simpler decoder for special applications.
   - `zlib.Z_HUFFMAN_ONLY` Use to force Huffman encoding only (no string match).
   - `zlib.Z_RLE` Use to limit match distances to one (run-length encoding).
     This is designed to be almost as fast as `zlib.Z_HUFFMAN_ONLY`, but give
     better compression for PNG image data.

 **Note** in the list above, `zlib` is from `zlib = require('zlib')`.

 ##### 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 or any string
 accepted by the [bytes](https://www.npmjs.com/package/bytes) module.

 **Note** this is only an advisory setting; if the response size cannot be determined
 at the time the response headers are written, then it is assumed the response is
 _over_ the threshold. To guarantee the response size can be determined, be sure
 set a `Content-Length` response header.

 ##### windowBits

 The default value is `zlib.Z_DEFAULT_WINDOWBITS`, or `15`.

 See [Node.js documentation](http://nodejs.org/api/zlib.html#zlib_memory_usage_tuning)
 regarding the usage.

 #### .filter

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

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

 var app = express()
 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.

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

 var app = express()

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

 // add all 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.

 ```js
 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](LICENSE)

 [npm-image]: https://img.shields.io/npm/v/compression.svg
 [npm-url]: https://npmjs.org/package/compression
 [travis-image]: https://img.shields.io/travis/expressjs/compression/master.svg
 [travis-url]: https://travis-ci.org/expressjs/compression
 [coveralls-image]: https://img.shields.io/coveralls/expressjs/compression/master.svg
 [coveralls-url]: https://coveralls.io/r/expressjs/compression?branch=master
 [downloads-image]: https://img.shields.io/npm/dm/compression.svg
 [downloads-url]: https://npmjs.org/package/compression
	# compression

	[![NPM Version][npm-image]][npm-url]
	[![NPM Downloads][downloads-image]][downloads-url]
	[![Build Status][travis-image]][travis-url]
	[![Test Coverage][coveralls-image]][coveralls-url]

	Node.js compression middleware.

	The following compression codings are supported:

	- deflate
	- gzip

	## Install

	This is a [Node.js](https://nodejs.org/en/) module available through the
	[npm registry](https://www.npmjs.com/). Installation is done using the
	[`npm install` command](https://docs.npmjs.com/getting-started/installing-npm-packages-locally):

	```bash
	$ npm install compression
	```

	## API

	<!-- eslint-disable no-unused-vars -->

	```js
	var compression = require('compression')
	```

	### compression([options])

	Returns the compression middleware using the given `options`. The middleware
	will attempt to compress response bodies for all request that traverse through
	the middleware, based on the given `options`.

	This middleware will never compress responses that include a `Cache-Control`
	header with the [`no-transform` directive](https://tools.ietf.org/html/rfc7234#section-5.2.2.4),
	as compressing will transform the body.

	#### Options

	`compression()` accepts these properties in the options object. In addition to
	those listed below, [zlib](http://nodejs.org/api/zlib.html) options may be
	passed in to the options object.

	##### chunkSize

	The default value is `zlib.Z_DEFAULT_CHUNK`, or `16384`.

	See [Node.js documentation](http://nodejs.org/api/zlib.html#zlib_memory_usage_tuning)
	regarding the usage.

	##### 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](https://www.npmjs.com/package/compressible)
	module to determine if `res.getHeader('Content-Type')` is compressible.

	##### level

	The level of zlib compression to apply to responses. A higher level will result
	in better compression, but will take longer to complete. A lower level will
	result in less compression, but will be much faster.

	This is an integer in the range of `0` (no compression) to `9` (maximum
	compression). The special value `-1` can be used to mean the "default
	compression level", which is a default compromise between speed and
	compression (currently equivalent to level 6).

	- `-1` Default compression level (also `zlib.Z_DEFAULT_COMPRESSION`).
	- `0` No compression (also `zlib.Z_NO_COMPRESSION`).
	- `1` Fastest compression (also `zlib.Z_BEST_SPEED`).
	- `2`
	- `3`
	- `4`
	- `5`
	- `6` (currently what `zlib.Z_DEFAULT_COMPRESSION` points to).
	- `7`
	- `8`
	- `9` Best compression (also `zlib.Z_BEST_COMPRESSION`).

	The default value is `zlib.Z_DEFAULT_COMPRESSION`, or `-1`.

	Note in the list above, `zlib` is from `zlib = require('zlib')`.

	##### memLevel

	This specifies how much memory should be allocated for the internal compression
	state and is an integer in the range of `1` (minimum level) and `9` (maximum
	level).

	The default value is `zlib.Z_DEFAULT_MEMLEVEL`, or `8`.

	See [Node.js documentation](http://nodejs.org/api/zlib.html#zlib_memory_usage_tuning)
	regarding the usage.

	##### strategy

	This is used to tune the compression algorithm. This value only affects the
	compression ratio, not the correctness of the compressed output, even if it
	is not set appropriately.

	- `zlib.Z_DEFAULT_STRATEGY` Use for normal data.
	- `zlib.Z_FILTERED` Use for data produced by a filter (or predictor).
	Filtered data consists mostly of small values with a somewhat random
	distribution. In this case, the compression algorithm is tuned to
	compress them better. The effect is to force more Huffman coding and less
	string matching; it is somewhat intermediate between `zlib.Z_DEFAULT_STRATEGY`
	and `zlib.Z_HUFFMAN_ONLY`.
	- `zlib.Z_FIXED` Use to prevent the use of dynamic Huffman codes, allowing
	for a simpler decoder for special applications.
	- `zlib.Z_HUFFMAN_ONLY` Use to force Huffman encoding only (no string match).
	- `zlib.Z_RLE` Use to limit match distances to one (run-length encoding).
	This is designed to be almost as fast as `zlib.Z_HUFFMAN_ONLY`, but give
	better compression for PNG image data.

	Note in the list above, `zlib` is from `zlib = require('zlib')`.

	##### 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 or any string
	accepted by the [bytes](https://www.npmjs.com/package/bytes) module.

	Note this is only an advisory setting; if the response size cannot be determined
	at the time the response headers are written, then it is assumed the response is
	_over_ the threshold. To guarantee the response size can be determined, be sure
	set a `Content-Length` response header.

	##### windowBits

	The default value is `zlib.Z_DEFAULT_WINDOWBITS`, or `15`.

	See [Node.js documentation](http://nodejs.org/api/zlib.html#zlib_memory_usage_tuning)
	regarding the usage.

	#### .filter

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

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

	var app = express()
	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.

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

	var app = express()

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

	// add all 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.

	```js
	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](LICENSE)

	[npm-image]: https://img.shields.io/npm/v/compression.svg
	[npm-url]: https://npmjs.org/package/compression
	[travis-image]: https://img.shields.io/travis/expressjs/compression/master.svg
	[travis-url]: https://travis-ci.org/expressjs/compression
	[coveralls-image]: https://img.shields.io/coveralls/expressjs/compression/master.svg
	[coveralls-url]: https://coveralls.io/r/expressjs/compression?branch=master
	[downloads-image]: https://img.shields.io/npm/dm/compression.svg
	[downloads-url]: https://npmjs.org/package/compression