feat(log): helper to capture logs in an async stack

@xen-orchestra/log/.USAGE.md

@@ -192,3 +192,66 @@ app ERROR Something went wrong
 app ERROR duplicates of the previous log were hidden { nDuplicates: 2 }
 app INFO This is a different message
 ```
+
+#### Capture
+
+> Allow capturing all logs emitted during a call, even through asynchronous operations.
+
+Before being able to use this feature, you need to add the transport:
+
+```js
+import { configure } from '@xen-orchestra/log/configure'
+import { createCaptureTransport } from '@xen-orchestra/log/capture'
+import createConsoleTransport from '@xen-orchestra/log/transports/console'
+
+// transport that will be used globally, when not in a captured environment
+const fallbackTransport = {
+  filter: process.env.DEBUG,
+  level: 'warn',
+
+  transport: createConsoleTransport(),
+}
+
+// create the capture transport and pass it the fallback one
+const captureTransport = createCaptureTransport(fallbackTransport)
+
+// configure @xen-orchestra/log to use our transport
+configure(captureTransport)
+```
+
+Now the `captureLogs(onLog, fn)` can be used:
+
+```js
+import { captureLogs } from '@xen-orchestra/log/capture'
+import { createLogger } from '@xen-orchestra/log'
+
+const logger = createLogger('my-logger')
+
+await captureLogs(
+  log => {
+    // every logs emitted in the async context of `fn` will arrive here
+    //
+    // do not emit logs in this function or this will create a loop.
+  },
+  async () => {
+    logger.debug('synchronous logs are captured')
+
+    setTimeout(() => {
+      logger.debug('logs from asynchronous callbacks too')
+    }, 50)
+
+    await new Promise(resolve => setTimeout(resolve, 50))
+
+    logger.debug('logs in async functions or promise chains too')
+
+    // To escape capture, run code in `captureLogs` with `undefined`
+    // as the first param
+    captureLogs(undefined, () => {
+      logger.debug('this log will not be captured')
+    })
+
+    // Returned value and error is forwarded by `captureLogs`
+    return Math.PI
+  }
+)
+```

@xen-orchestra/log/README.md

@@ -211,6 +211,69 @@ app ERROR duplicates of the previous log were hidden { nDuplicates: 2 }
 app INFO This is a different message
 ```
 
+#### Capture
+
+> Allow capturing all logs emitted during a call, even through asynchronous operations.
+
+Before being able to use this feature, you need to add the transport:
+
+```js
+import { configure } from '@xen-orchestra/log/configure'
+import { createCaptureTransport } from '@xen-orchestra/log/capture'
+import createConsoleTransport from '@xen-orchestra/log/transports/console'
+
+// transport that will be used globally, when not in a captured environment
+const fallbackTransport = {
+  filter: process.env.DEBUG,
+  level: 'warn',
+
+  transport: createConsoleTransport(),
+}
+
+// create the capture transport and pass it the fallback one
+const captureTransport = createCaptureTransport(fallbackTransport)
+
+// configure @xen-orchestra/log to use our transport
+configure(captureTransport)
+```
+
+Now the `captureLogs(onLog, fn)` can be used:
+
+```js
+import { captureLogs } from '@xen-orchestra/log/capture'
+import { createLogger } from '@xen-orchestra/log'
+
+const logger = createLogger('my-logger')
+
+await captureLogs(
+  log => {
+    // every logs emitted in the async context of `fn` will arrive here
+    //
+    // do not emit logs in this function or this will create a loop.
+  },
+  async () => {
+    logger.debug('synchronous logs are captured')
+
+    setTimeout(() => {
+      logger.debug('logs from asynchronous callbacks too')
+    }, 50)
+
+    await new Promise(resolve => setTimeout(resolve, 50))
+
+    logger.debug('logs in async functions or promise chains too')
+
+    // To escape capture, run code in `captureLogs` with `undefined`
+    // as the first param
+    captureLogs(undefined, () => {
+      logger.debug('this log will not be captured')
+    })
+
+    // Returned value and error is forwarded by `captureLogs`
+    return Math.PI
+  }
+)
+```
+
 ## Contributions
 
 Contributions are _very_ welcomed, either on the documentation or on

@xen-orchestra/log/capture.js

@@ -0,0 +1,39 @@
+'use strict'
+
+// Even though the lib is compatible with Node >=8.3,
+// the capture feature requires Node >=13.10
+//
+// eslint-disable-next-line n/no-unsupported-features/node-builtins
+const { AsyncLocalStorage } = require('node:async_hooks')
+
+const createTransport = require('./_createTransport.js')
+
+// stored in the global context so that various versions of the library can interact.
+const symbol = Symbol.for('@xen-orchestra/log/capture')
+const asyncStorage = global[symbol] || (global[symbol] = new AsyncLocalStorage())
+
+/**
+ * Runs `fn` capturing all emitted logs (sync and async) and forward them to `onLog`.
+ *
+ * @template {(...args: any) => any} F
+ * @param {undefined | (log: object) => void} onLog
+ * @param {F} fn
+ * @returns {ReturnType<F>}
+ */
+exports.captureLogs = function captureLogs(onLog, fn) {
+  return asyncStorage.run(onLog, fn)
+}
+
+/**
+ * Creates a transport for the `captureLogs` feature.
+ *
+ * @param {*} fallback - The transport to use as a fallback when not capturing
+ * @returns {(log: object) => void}
+ */
+exports.createCaptureTransport = function createCaptureTransport(fallback) {
+  fallback = fallback === undefined ? Function.prototype : createTransport(fallback)
+
+  return function captureTransport(log) {
+    ;(asyncStorage.getStore() || fallback)(log)
+  }
+}

@xen-orchestra/log/package.json

@@ -4,6 +4,12 @@
   "version": "0.6.0",
   "license": "ISC",
   "description": "Logging system with decoupled producers/consumer",
+  "keywords": [
+    "async",
+    "asynchronous",
+    "capture",
+    "context"
+  ],
   "homepage": "https://github.com/vatesfr/xen-orchestra/tree/master/@xen-orchestra/log",
   "bugs": "https://github.com/vatesfr/xen-orchestra/issues",
   "repository": {

CHANGELOG.unreleased.md

@@ -38,6 +38,7 @@
 
 <!--packages-start-->
 
+- @xen-orchestra/log minor
 - xo-server minor
 - xo-server-perf-alert minor
 - xo-server-sdn-controller patch