From a13ff0a56313b23ab45e077ffa941527773d6eed Mon Sep 17 00:00:00 2001
From: Andrey Pechkurov <apechkurov@gmail.com>
Date: Fri, 5 Jun 2020 11:47:43 +0300
Subject: [PATCH] async_hooks: add bindToAsyncScope method to AsyncResource

---
 doc/api/async_hooks.md                        | 32 +++++++++++++++++++
 lib/async_hooks.js                            |  7 ++++
 ...der.api.async-resource.bindToAsyncScope.js | 14 ++++++++
 3 files changed, 53 insertions(+)
 create mode 100644 test/async-hooks/test-embedder.api.async-resource.bindToAsyncScope.js

diff --git a/doc/api/async_hooks.md b/doc/api/async_hooks.md
index 7d6bd72e7de1fa..b74b1af9117590 100644
--- a/doc/api/async_hooks.md
+++ b/doc/api/async_hooks.md
@@ -662,6 +662,10 @@ const asyncResource = new AsyncResource(
 // * restore the original execution context
 asyncResource.runInAsyncScope(fn, thisArg, ...args);
 
+// Return a wrapper function that always runs in the execution context
+// of the resource.
+asyncResource.bindToAsyncScope(fn);
+
 // Call AsyncHooks destroy callbacks.
 asyncResource.emitDestroy();
 
@@ -723,6 +727,34 @@ of the async resource. This will establish the context, trigger the AsyncHooks
 before callbacks, call the function, trigger the AsyncHooks after callbacks, and
 then restore the original execution context.
 
+#### `asyncResource.bindToAsyncScope(fn)`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `fn` {Function} The function to be wrapped.
+
+Return a wrapper function for the supplied function. The returned funtion, when
+it is run, will have the same context as if it was run with
+`asyncResource.runInAsyncScope()`.
+
+The following is a simple demonstration of `asyncResource.bindToAsyncScope()`:
+
+```js
+const { createServer } = require('http');
+const { AsyncResource, executionAsyncId } = require('async_hooks');
+
+const server = createServer(function(req, res) {
+  const asyncResource = new AsyncResource('request');
+  const asyncId = asyncResource.asyncId();
+  // The listener will always run in the execution context of `asyncResource`.
+  req.on('close', asyncResource.bindToAsyncScope(() => {
+    console.log(executionAsyncId()); // Prints the value of `asyncId`.
+  }));
+  res.end();
+}).listen(3000);
+```
+
 #### `asyncResource.emitDestroy()`
 
 * Returns: {AsyncResource} A reference to `asyncResource`.
diff --git a/lib/async_hooks.js b/lib/async_hooks.js
index 9e287405f8af0b..24a92198582f2c 100644
--- a/lib/async_hooks.js
+++ b/lib/async_hooks.js
@@ -196,6 +196,13 @@ class AsyncResource {
     }
   }
 
+  bindToAsyncScope(fn) {
+    const self = this;
+    return function() {
+      return self.runInAsyncScope(fn, this, ...arguments);
+    };
+  }
+
   emitDestroy() {
     if (this[destroyedSymbol] !== undefined) {
       this[destroyedSymbol].destroyed = true;
diff --git a/test/async-hooks/test-embedder.api.async-resource.bindToAsyncScope.js b/test/async-hooks/test-embedder.api.async-resource.bindToAsyncScope.js
new file mode 100644
index 00000000000000..b0295958e5a873
--- /dev/null
+++ b/test/async-hooks/test-embedder.api.async-resource.bindToAsyncScope.js
@@ -0,0 +1,14 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+const { AsyncResource, executionAsyncId } = require('async_hooks');
+
+const a = new AsyncResource('foobar');
+
+function foo(bar) {
+  assert.strictEqual(executionAsyncId(), a.asyncId());
+  return bar;
+}
+
+const ret = a.bindToAsyncScope(foo)('baz');
+assert.strictEqual(ret, 'baz');