bufferutil
WebSocket buffer utils
About
WebSocket buffer utils
Live mirror of the GitHub README. Updated whenever the repo's default branch changes.
bufferutil
bufferutil is what makes ws fast. It provides some utilities to efficiently
perform some operations such as masking and unmasking the data payload of
WebSocket frames.
Installation
npm install bufferutil --save-optional
The --save-optional flag tells npm to save the package in your package.json
under the
optionalDependencies
key.
API
The module exports two functions. To maximize performance, parameters are not validated. It is the caller's responsibility to ensure that they are correct.
bufferUtil.mask(source, mask, output, offset, length)
Masks a buffer using the given masking-key as specified by the WebSocket protocol.
Arguments
source- The buffer to mask.mask- A buffer representing the masking-key.output- The buffer where to store the result.offset- The offset at which to start writing.length- The number of bytes to mask.
Example
'use strict';
const bufferUtil = require('bufferutil');
const crypto = require('crypto');
const source = crypto.randomBytes(10);
const mask = crypto.randomBytes(4);
bufferUtil.mask(source, mask, source, 0, source.length);
bufferUtil.unmask(buffer, mask)
Unmasks a buffer using the given masking-key as specified by the WebSocket protocol.
Arguments
buffer- The buffer to unmask.mask- A buffer representing the masking-key.
Example
'use strict';
const bufferUtil = require('bufferutil');
const crypto = require('crypto');
const buffer = crypto.randomBytes(10);
const mask = crypto.randomBytes(4);
bufferUtil.unmask(buffer, mask);
License
Quick facts
npm install bufferutilHow Sourcemap Explorer detects bufferutil
We catch bufferutil from two complementary signals: bundled source paths and the embedded package.json. Modern bundlers (webpack, Vite, esbuild, Rollup, Turbopack) preserve the original node_modules/bufferutil/ paths inside the JavaScript sourcemap's sources[] array — that's the canonical signal. When the matching package.json is also captured in sourcesContent[], we read the exact version field — patch number included. No regex guessing, no version inference.
- 1
Confirm the site exposes sourcemaps
In DevTools Network, check the response headers of any application script for `SourceMap` or `X-SourceMap`. Failing that, fetch the script's last 4 KB and look for a `//# sourceMappingURL=` comment.
- 2
Find the package in the bundle
Open DevTools → Network → reload. Click any application script and look at its sourcemap. Inside, search `sources[]` for entries matching `node_modules/bufferutil/` — every match confirms the package is bundled. The matching `sourcesContent[i]` for `node_modules/bufferutil/package.json` gives you the exact installed version.
- 3
Read the version directly from package.json
Run `jq -r '. as $m | $m.sources | to_entries[] | select(.value | endswith("node_modules/bufferutil/package.json")) | $m.sourcesContent[.key] | fromjson | .version' bundle.js.map`. Sourcemap Explorer automates the same query in the popup.
Recent versions
FAQ
What is bufferutil used for?
WebSocket buffer utils
How can I tell if a website is using bufferutil?
Open the page in Chrome with the Sourcemap Explorer extension installed and read the Stack tab. We catch `bufferutil` from two complementary signals: `node_modules/bufferutil/` paths inside the JavaScript sourcemap, and the embedded `package.json` we read for exact-version detection. Without the extension you can do the same lookup manually in DevTools — the steps are listed in the "How Sourcemap Explorer detects" section above.
What is the latest version of bufferutil?
4.1.0, as published on the npm registry. The "Recent versions" table on this page lists the most recent 8 releases with their release dates. Sourcemap Explorer reports the version actually bundled into a site, which can lag the latest release by months on real-world deployments.
Where can I read more?
Project homepage: https://github.com/websockets/bufferutil. Source code: https://github.com/websockets/bufferutil. Published on npm: https://www.npmjs.com/package/bufferutil. Licensed as MIT.
Detected by Sourcemap Explorer
When a bundle ships sourcemaps, we read the embedded package.json for bufferutil and report the precise version. Without sourcemaps, an import / require in the page's scripts is enough to flag it.