From f7e2c546b37161b1d3891f4e44a55ed26e1a5012 Mon Sep 17 00:00:00 2001
From: Robert Nagy <ronagy@icloud.com>
Date: Mon, 2 Oct 2023 14:25:51 +0200
Subject: [PATCH] stream: avoid unnecessary drain for sync stream

PR-URL: https://github.com/nodejs/node/pull/50014
---
 lib/internal/streams/writable.js | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/lib/internal/streams/writable.js b/lib/internal/streams/writable.js
index 5800c9df171ff2..955b6283e6a105 100644
--- a/lib/internal/streams/writable.js
+++ b/lib/internal/streams/writable.js
@@ -108,6 +108,7 @@ const kWriteCb = 1 << 26;
 const kExpectWriteCb = 1 << 27;
 const kAfterWriteTickInfo = 1 << 28;
 const kAfterWritePending = 1 << 29;
+const kIsDuplex = 1 << 30;
 
 // TODO(benjamingr) it is likely slower to do it this way than with free functions
 function makeBitMapDescriptor(bit) {
@@ -286,6 +287,7 @@ function WritableState(options, stream, isDuplex) {
 
   if (options && options.objectMode) this.state |= kObjectMode;
   if (isDuplex && options && options.writableObjectMode) this.state |= kObjectMode;
+  if (isDuplex) this.state |= kIsDuplex;
 
   // The point at which write() starts returning false
   // Note: 0 is a valid value, means that we always return false if
@@ -513,13 +515,7 @@ function writeOrBuffer(stream, state, chunk, encoding, callback) {
 
   state.length += len;
 
-  // stream._write resets state.length
-  const ret = state.length < state.highWaterMark;
-
-  // We must ensure that previous needDrain will not be reset to false.
-  if (!ret) {
-    state.state |= kNeedDrain;
-  }
+  const prevLen = state.length;
 
   if ((state.state & (kWriting | kErrored | kCorked | kConstructed)) !== kConstructed) {
     state.buffered.push({ chunk, encoding, callback });
@@ -539,6 +535,16 @@ function writeOrBuffer(stream, state, chunk, encoding, callback) {
     state.state &= ~kSync;
   }
 
+  const ret = (
+    ((state.state & kIsDuplex) === 0 || stream._readableState.ended !== true) ?
+      state.length < state.highWaterMark :
+      prevLen < state.highWaterMark
+  );
+
+  if (!ret) {
+    state.state |= kNeedDrain;
+  }
+
   // Return false if errored or destroyed in order to break
   // any synchronous while(stream.write(data)) loops.
   return ret && (state.state & (kDestroyed | kErrored)) === 0;