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[feature]: zlib deflate concurrency limit
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STRML committed Sep 11, 2017
1 parent 80445e7 commit 946edc2
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Showing 3 changed files with 59 additions and 3 deletions.
5 changes: 5 additions & 0 deletions doc/ws.md
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Expand Up @@ -76,6 +76,10 @@ provided then that is extension parameters:
- `memLevel` {Number} The value of zlib's `memLevel` param (1-9, default 8).
- `threshold` {Number} Payloads smaller than this will not be compressed.
Defaults to 1024 bytes.
- `concurrencyLimit` {Number} The number of concurrent calls to zlib.
Calls above this limit will be queued. Default 10. You usually won't
need to touch this option. See [concurrency-limit][this issue] for more
details.

If a property is empty then either an offered configuration or a default value
is used.
Expand Down Expand Up @@ -425,4 +429,5 @@ Forcibly close the connection.

The URL of the WebSocket server. Server clients don't have this attribute.

[concurrency-limit]: https://github.com/websockets/ws/issues/1202
[permessage-deflate]: https://tools.ietf.org/html/draft-ietf-hybi-permessage-compression-19
56 changes: 53 additions & 3 deletions lib/PerMessageDeflate.js
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Expand Up @@ -2,6 +2,7 @@

const safeBuffer = require('safe-buffer');
const zlib = require('zlib');
const Limiter = require('async-limiter');

const bufferUtil = require('./BufferUtil');

Expand All @@ -10,6 +11,14 @@ const Buffer = safeBuffer.Buffer;
const TRAILER = Buffer.from([0x00, 0x00, 0xff, 0xff]);
const EMPTY_BLOCK = Buffer.from([0x00]);

// We limit zlib concurrency, which prevents severe memory fragmentation
// as documented in https://github.com/nodejs/node/issues/8871#issuecomment-250915913
// and https://github.com/websockets/ws/issues/1202
//
// Intentionally global; it's the global thread pool that's
// an issue.
let zlibLimiter;

/**
* Per-message Deflate implementation.
*/
Expand All @@ -25,6 +34,13 @@ class PerMessageDeflate {
this._inflate = null;

this.params = null;

if (!zlibLimiter) {
const concurrency = this._options.concurrencyLimit !== undefined
? this._options.concurrencyLimit
: 10;
zlibLimiter = new Limiter({ concurrency });
}
}

static get extensionName () {
Expand Down Expand Up @@ -249,14 +265,48 @@ class PerMessageDeflate {
}

/**
* Decompress data.
* Decompress data. Concurrency limited by async-limiter.
*
* @param {Buffer} data Compressed data
* @param {Boolean} fin Specifies whether or not this is the last fragment
* @param {Function} callback Callback
* @public
*/
decompress (data, fin, callback) {
zlibLimiter.push((done) => {
this._decompress(data, fin, (err, result) => {
done();
callback(err, result);
});
});
}

/**
* Compress data. Concurrency limited by async-limiter.
*
* @param {Buffer} data Data to compress
* @param {Boolean} fin Specifies whether or not this is the last fragment
* @param {Function} callback Callback
* @public
*/
compress (data, fin, callback) {
zlibLimiter.push((done) => {
this._compress(data, fin, (err, result) => {
done();
callback(err, result);
});
});
}

/**
* Decompress data.
*
* @param {Buffer} data Compressed data
* @param {Boolean} fin Specifies whether or not this is the last fragment
* @param {Function} callback Callback
* @private
*/
_decompress (data, fin, callback) {
const endpoint = this._isServer ? 'client' : 'server';

if (!this._inflate) {
Expand Down Expand Up @@ -322,9 +372,9 @@ class PerMessageDeflate {
* @param {Buffer} data Data to compress
* @param {Boolean} fin Specifies whether or not this is the last fragment
* @param {Function} callback Callback
* @public
* @private
*/
compress (data, fin, callback) {
_compress (data, fin, callback) {
if (!data || data.length === 0) {
process.nextTick(callback, null, EMPTY_BLOCK);
return;
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1 change: 1 addition & 0 deletions package.json
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Expand Up @@ -26,6 +26,7 @@
"lint": "eslint ."
},
"dependencies": {
"async-limiter": "~1.0.0",
"safe-buffer": "~5.1.0",
"ultron": "~1.1.0"
},
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