From c38d883336c3e91912bb98f5afb27f8d164df744 Mon Sep 17 00:00:00 2001
From: Kosta <Kosta-Github@users.noreply.github.com>
Date: Mon, 22 Jun 2020 18:09:32 +0200
Subject: [PATCH] fix drain() function for "Piping to writable streams from
 async iterators"

The sample code for ["Piping to writable streams from async iterators"](https://nodejs.org/docs/latest-v14.x/api/stream.html#stream_piping_to_writable_streams_from_async_iterators) is containing an event listener leak, since it registers 2 event listeners, but don't remove them again.

The `drain()` function has been changed to remove all the listeners that have been registered within that function in any case again.
---
 doc/api/stream.md | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/doc/api/stream.md b/doc/api/stream.md
index b195458cec9b4f..25d8880430c176 100644
--- a/doc/api/stream.md
+++ b/doc/api/stream.md
@@ -2890,20 +2890,32 @@ In the scenario of writing to a writable stream from an async iterator, ensure
 the correct handling of backpressure and errors.
 
 ```js
-const { once } = require('events');
 const finished = util.promisify(stream.finished);
 
 const writable = fs.createWriteStream('./file');
 
 function drain(writable) {
+  const resolve = () => Promise.resolve();
+  const rejectError = (err) => Promise.reject(err);
+  const rejectPrematureClose = () => Promise.reject(new Error('premature close of writable stream'));
+
   if (writable.destroyed) {
-    return Promise.reject(new Error('premature close'));
+    return rejectPrematureClose();
+  }
+
+  try {
+    // register event listeners and wait for whatever event gets emitted first
+    await Promise.race([
+      writable.once('drain', resolve),
+      writable.once('error', rejectError),
+      writable.once('close', rejectPrematureClose),
+    ]);
+  } finally {
+    // ensure that all the registered event listeners get removed again
+    writable.removeListener('drain', resolve);
+    writable.removeListener('error', rejectError);
+    writable.removeListener('close', rejectPrematureClose);
   }
-  return Promise.race([
-    once(writable, 'drain'),
-    once(writable, 'close')
-      .then(() => Promise.reject(new Error('premature close')))
-  ]);
 }
 
 async function pump(iterable, writable) {