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Notable Changes:
Diagnostics channel (experimental module):
`diagnostics_channel` is a new experimental module that provides an API
to create named channels to report arbitrary message data for
diagnostics purposes.
The module was initially introduced in Node.js v15.1.0 and is
backported to v14.17.0 to enable testing it at a larger scale.
With `diagnostics_channel`, Node.js core and module authors can publish
contextual data about what they are doing at a given time. This could
be the hostname and query string of a mysql query, for example. Just
create a named channel with `dc.channel(name)` and call
`channel.publish(data)` to send the data to any listeners to that
channel.
```js
const dc = require('diagnostics_channel');
const channel = dc.channel('mysql.query');
MySQL.prototype.query = function query(queryString, values, callback) {
// Broadcast query information whenever a query is made
channel.publish({
query: queryString,
host: this.hostname,
});
this.doQuery(queryString, values, callback);
};
```
Channels are like one big global event emitter but are split into
separate objects to ensure they get the best performance. If nothing is
listening to the channel, the publishing overhead should be as close to
zero as possible. Consuming channel data is as easy as using
`channel.subscribe(listener)` to run a function whenever a message is
published to that channel.
```js
const dc = require('diagnostics_channel');
const channel = dc.channel('mysql.query');
channel.subscribe(({ query, host }) => {
console.log(`mysql query to ${host}: ${query}`);
});
```
The data captured can be used to provide context for what an app is
doing at a given time. This can be used for things like augmenting
tracing data, tracking network and filesystem activity, logging
queries, and many other things. It's also a very useful data source
for diagnostics tools to provide a clearer picture of exactly what the
application is doing at a given point in the data they are presenting.
Contributed by Stephen Belanger (#34895).
UUID support in the crypto module:
The new `crypto.randomUUID()` method now allows to generate random
[RFC 4122](https://www.rfc-editor.org/rfc/rfc4122.txt) Version 4
UUID strings:
```js
const { randomUUID } = require('crypto');
console.log(randomUUID());
// 'aa7c91a1-f8fc-4339-b9db-f93fc7233429'
```
Contributed by James M Snell (#36729).
Experimental support for `AbortController` and `AbortSignal`:
Node.js 14.17.0 adds experimental partial support for `AbortController`
and `AbortSignal`.
Both constructors can be enabled globally using the
`--experimental-abortcontroller` flag.
Additionally, several Node.js APIs have been updated to support
`AbortSignal` for cancellation.
It is not mandatory to use the built-in constructors with them. Any
spec-compliant third-party alternatives should be compatible.
`AbortSignal` support was added to the following methods:
* `child_process.exec`
* `child_process.execFile`
* `child_process.fork`
* `child_process.spawn`
* `dgram.createSocket`
* `events.on`
* `events.once`
* `fs.readFile`
* `fs.watch`
* `fs.writeFile`
* `http.request`
* `https.request`
* `http2Session.request`
* The promisified variants of `setImmediate` and `setTimeout`
Other notable changes:
* doc:
* revoke deprecation of legacy url, change status to legacy (James M Snell) (#37784)
* add legacy status to stability index (James M Snell) (#37784)
* upgrade stability status of report API (Gireesh Punathil) (#35654)
* deps:
* V8: Backport various patches for Apple Silicon support (BoHong Li) (#38051)
* update ICU to 68.1 (Michaël Zasso) (#36187)
* upgrade to libuv 1.41.0 (Colin Ihrig) (#37360)
* http:
* add http.ClientRequest.getRawHeaderNames() (simov) (#37660)
* report request start and end with diagnostics\_channel (Stephen Belanger) (#34895)
* util:
* add getSystemErrorMap() impl (eladkeyshawn) (#38101)
PR-URL: #38507
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