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Node.js compression middleware with brotli and zopfli support

Version published
Install size
2.30 MB



4.1.3 (2021-04-14)

Bug Fixes

  • update dependences (2ee496c)




The original shrink-ray appears to be abandoned. This mirror has all the dependencies up-to-date.

Version License Build status Coverage Dependencies Dev Dependencies Greenkeeper badge

Node.js compression middleware with modern codings like brotli and zopfli.

The following compression codings are supported:

  • deflate
  • gzip
  • brotli
  • zopfli (for asynchronous compression of static assets only)

In addition, if a response contains an ETag, shrink-ray-current will cache the compressed result for later requests and even re-compress it asynchronously at the highest possible compression (using zopfli for gzip and deflate and brotli quality 11 for brotli). This makes it possible to use the best possible compression algorithms for static content (saving as much as 25% over standard gzip) without sacrificing runtime performance.

The combination of caching and use of better compression algorithms makes shrink-ray serve static files in our benchmark 3x faster than compression while using only one quarter as much CPU time.

Note: this project was forked from compression, the standard Express/Connect compression middleware, and it stands on the shoulders of that impressive project.

Table of Contents


You must first install node, npm, and the node native build toolchain.

npm install shrink-ray-current

Peer Dependencies

The brotli and zopfli algorithms rely on Node modules with native bindings. Some environments may not be able to build these dependencies, but shrink-ray tries to run even when they are absent; it just falls back to gzip.

Therefore, the iltorb and node-zopfli-es modules are listed as peerDependencies in package.json. This is for two reasons:

  • shrink-ray will install successfully without them and fall back to gzip
  • Projects using shrink-ray can specify their own version ranges of these dependencies for maximum control

Add them manually to your package.json as optionalDependencies:

"optionalDependencies": {
  "iltorb": "~2.0.0",
  "node-zopfli-es": "~1.0.3"

Then, run npm install again.

(Node >=11.8 has Brotli compression built in, but shrink-ray supports prior versions of Node as well. If your version of Node is >=11.8, the iltorb module is not necessary at runtime; however, you'll still see a warning at install time.)


const shrinkRay = require('shrink-ray-current');


Returns the shrink-ray 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, as compressing will transform the body.


shrinkRay() accepts these properties in the options object.

Note that shrink-ray options are backward-compatible with compression, but we have also moved all of the gzip/deflate/zlib-specific parameters into a sub-object called zlib. If you use zlib parameters at the root level of options in shrink-ray, you will get a deprecation warning.


Whether to use node-zopfli-es (true) or zlib (false) for gzip compression. Defaults to true.


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.


A function to decide if the compressed response should be cached for later use. This function is called as cache(req, res) and is expected to return true if the compressed response should be cached and false if the response should not be cached. Note that shrink-ray uses ETags to ensure that a cache entry is appropriate to return, so it will never cache a response that does not include an ETag, even if the cache function returns true.

When a response is cached, it will be asynchronously re-encoded at the highest quality level available for the compression algorithm in question (zopfli for gzip and deflate, and brotli quality 11 for brotli). These quality levels are generally not acceptable for use when responding to a request in real-time because they are too CPU-intensive, but they can be performed in the background so that subsequent requests get the highest compression levels available.

By default, shrink-ray caches any response that has an ETag header associated with it, which means it should work out of the box with express.static, caching static files with the highest available compression. If you serve a large number of dynamic files with ETags, you may want to have your cache function restrict caching to your static file directory so as to avoid thrashing the cache and wasting CPU time on expensive compressions.


The approximate size, in bytes, of the cache. This is a number of bytes, any string accepted by the bytes module, or false to indicate no caching. The default cacheSize is 128mb.

The size includes space for the URL of the cached resources and the compressed bytes of the responses. It does not, however, include overhead for JavaScript objects, so the actual total amount of memory taken up by the cache will be somewhat larger than cacheSize in practice.

When deciding how large to make your cache, remember that every cached resource in your app may have as many as three compressed entries: one each for gzip, deflate, and brotli.


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.

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.


There is a sub-object of the options object called zlib which contains all of the parameters related to gzip and deflate. In addition to those listed below, zlib options may be passed in to the zlib sub-object.

Also note that to temporarily preserve backwards compatibility with compression, all of these zlib parameters can be included at the root level of the options object. However, having zlib parameters at the root level is deprecated, and we plan to remove it.


The default value is zlib.Z_DEFAULT_CHUNK, or 16384.

See Node.js documentation regarding the usage.


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').


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 regarding the usage.


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').


The default value is zlib.Z_DEFAULT_WINDOWBITS, or 15.

See Node.js documentation regarding the usage.


To control the parameters of the brotli algorithm, pass in child object at the key brotli with one or more of the following brotli algorithm parameters: lgblock, lgwin, mode, or quality.

Note that unlike the standard brotli library, which defaults to quality 11, this library defaults to quality 4, which is generally more appropriate for dynamic content.


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

app.use(shrinkRay({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 shrinkRay.filter(req, res);


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



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.

const shrinkRay = require('shrink-ray-current');
const express = require('express');
const app = express();

// compress all requests

// 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.

const shrinkRay = require('shrink-ray-current');
const express   = require('express');
const app       = express();

// compress responses

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

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

    // !!! this is the important part
  }, 2000);

  res.on('close', () => {



Last updated on 14 Apr 2021

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