From 45d2f4dd3c0c9d2c6341be441ef3fc6aff46a7a6 Mon Sep 17 00:00:00 2001
From: James M Snell <jasnell@gmail.com>
Date: Thu, 30 Jul 2020 19:53:32 -0700
Subject: [PATCH] async_hooks: add AsyncResource.bind utility
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Creates an internal AsyncResource and binds a function to it,
ensuring that the function is invoked within execution context
in which bind was called.

PR-URL: https://github.com/nodejs/node/pull/34574
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Andrey Pechkurov <apechkurov@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
---
 doc/api/async_hooks.md                   | 36 ++++++++++++++++++++----
 lib/async_hooks.js                       | 24 ++++++++++++++++
 test/parallel/test-asyncresource-bind.js | 35 +++++++++++++++++++++++
 3 files changed, 90 insertions(+), 5 deletions(-)
 create mode 100644 test/parallel/test-asyncresource-bind.js

diff --git a/doc/api/async_hooks.md b/doc/api/async_hooks.md
index 8080e628617bde..a812f6998457f3 100644
--- a/doc/api/async_hooks.md
+++ b/doc/api/async_hooks.md
@@ -733,6 +733,32 @@ class DBQuery extends AsyncResource {
 }
 ```
 
+#### `static AsyncResource.bind(fn[, type])`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `fn` {Function} The function to bind to the current execution context.
+* `type` {string} An optional name to associate with the underlying
+  `AsyncResource`.
+
+Binds the given function to the current execution context.
+
+The returned function will have an `asyncResource` property referencing
+the `AsyncResource` to which the function is bound.
+
+#### `asyncResource.bind(fn)`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `fn` {Function} The function to bind to the current `AsyncResource`.
+
+Binds the given function to execute to this `AsyncResource`'s scope.
+
+The returned function will have an `asyncResource` property referencing
+the `AsyncResource` to which the function is bound.
+
 #### `asyncResource.runInAsyncScope(fn[, thisArg, ...args])`
 <!-- YAML
 added: v9.6.0
@@ -904,12 +930,12 @@ const { createServer } = require('http');
 const { AsyncResource, executionAsyncId } = require('async_hooks');
 
 const server = createServer((req, res) => {
-  const asyncResource = new AsyncResource('request');
-  // The listener will always run in the execution context of `asyncResource`.
-  req.on('close', asyncResource.runInAsyncScope.bind(asyncResource, () => {
-    // Prints: true
-    console.log(asyncResource.asyncId() === executionAsyncId());
+  req.on('close', AsyncResource.bind(() => {
+    // Execution context is bound to the current outer scope.
   }));
+  req.on('close', () => {
+    // Execution context is bound to the scope that caused 'close' to emit.
+  });
   res.end();
 }).listen(3000);
 ```
diff --git a/lib/async_hooks.js b/lib/async_hooks.js
index 4f7f03c3bf4aff..dddf6501752c52 100644
--- a/lib/async_hooks.js
+++ b/lib/async_hooks.js
@@ -2,6 +2,7 @@
 
 const {
   NumberIsSafeInteger,
+  ObjectDefineProperties,
   ReflectApply,
   Symbol,
 } = primordials;
@@ -9,6 +10,7 @@ const {
 const {
   ERR_ASYNC_CALLBACK,
   ERR_ASYNC_TYPE,
+  ERR_INVALID_ARG_TYPE,
   ERR_INVALID_ASYNC_ID
 } = require('internal/errors').codes;
 const { validateString } = require('internal/validators');
@@ -208,6 +210,28 @@ class AsyncResource {
   triggerAsyncId() {
     return this[trigger_async_id_symbol];
   }
+
+  bind(fn) {
+    if (typeof fn !== 'function')
+      throw new ERR_INVALID_ARG_TYPE('fn', 'Function', fn);
+    const ret = this.runInAsyncScope.bind(this, fn);
+    ObjectDefineProperties(ret, {
+      'length': {
+        enumerable: true,
+        value: fn.length,
+      },
+      'asyncResource': {
+        enumerable: true,
+        value: this,
+      }
+    });
+    return ret;
+  }
+
+  static bind(fn, type) {
+    type = type || fn.name;
+    return (new AsyncResource(type || 'bound-anonymous-fn')).bind(fn);
+  }
 }
 
 const storageList = [];
diff --git a/test/parallel/test-asyncresource-bind.js b/test/parallel/test-asyncresource-bind.js
new file mode 100644
index 00000000000000..3aeed475aee126
--- /dev/null
+++ b/test/parallel/test-asyncresource-bind.js
@@ -0,0 +1,35 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const { AsyncResource, executionAsyncId } = require('async_hooks');
+
+const fn = common.mustCall(AsyncResource.bind(() => {
+  return executionAsyncId();
+}));
+
+setImmediate(() => {
+  const asyncId = executionAsyncId();
+  assert.notStrictEqual(asyncId, fn());
+});
+
+const asyncResource = new AsyncResource('test');
+
+[1, false, '', {}, []].forEach((i) => {
+  assert.throws(() => asyncResource.bind(i), {
+    code: 'ERR_INVALID_ARG_TYPE'
+  });
+});
+
+const fn2 = asyncResource.bind((a, b) => {
+  return executionAsyncId();
+});
+
+assert.strictEqual(fn2.asyncResource, asyncResource);
+assert.strictEqual(fn2.length, 2);
+
+setImmediate(() => {
+  const asyncId = executionAsyncId();
+  assert.strictEqual(asyncResource.asyncId(), fn2());
+  assert.notStrictEqual(asyncId, fn2());
+});