From dd496c2878318ebc9b130b07af29b26b03df02e0 Mon Sep 17 00:00:00 2001
From: Mattias Buelens <mattias@buelens.com>
Date: Sun, 1 Mar 2026 13:33:20 +0100
Subject: [PATCH 1/5] stream: optimize webstreams pipeTo

---
 lib/internal/webstreams/readablestream.js | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/lib/internal/webstreams/readablestream.js b/lib/internal/webstreams/readablestream.js
index 43cfcded03def4..b6a420ca4b214b 100644
--- a/lib/internal/webstreams/readablestream.js
+++ b/lib/internal/webstreams/readablestream.js
@@ -1573,10 +1573,7 @@ function readableStreamPipeTo(
       }
 
       // Trigger pull if needed after batch
-      if (source[kState].state === 'readable' &&
-          !controller[kState].closeRequested) {
-        readableStreamDefaultControllerCallPullIfNeeded(controller);
-      }
+      readableStreamDefaultControllerCallPullIfNeeded(controller);
 
       // Check if stream closed during batch
       if (source[kState].state === 'closed') {

From 3479d397f708d9c51251a839aab50cc993d4b03f Mon Sep 17 00:00:00 2001
From: Mattias Buelens <mattias@buelens.com>
Date: Sun, 1 Mar 2026 13:35:28 +0100
Subject: [PATCH 2/5] fixup! do not use writer public API

---
 lib/internal/webstreams/readablestream.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/internal/webstreams/readablestream.js b/lib/internal/webstreams/readablestream.js
index b6a420ca4b214b..2456d1798f158a 100644
--- a/lib/internal/webstreams/readablestream.js
+++ b/lib/internal/webstreams/readablestream.js
@@ -127,6 +127,7 @@ const {
   writableStreamAbort,
   writableStreamCloseQueuedOrInFlight,
   writableStreamDefaultWriterCloseWithErrorPropagation,
+  writableStreamDefaultWriterGetDesiredSize,
   writableStreamDefaultWriterRelease,
   writableStreamDefaultWriterWrite,
 } = require('internal/webstreams/writablestream');
@@ -1564,7 +1565,7 @@ function readableStreamPipeTo(
 
         // Check backpressure after each write
         if (dest[kState].state === 'writable') {
-          const desiredSize = writer.desiredSize;
+          const desiredSize = writableStreamDefaultWriterGetDesiredSize(writer);
           if (desiredSize !== null && desiredSize <= 0) {
             // Backpressure - stop batch and wait for ready
             break;

From b8f166ca5aed82e1c1d8b53059f638f79a8f7cf1 Mon Sep 17 00:00:00 2001
From: Mattias Buelens <mattias@buelens.com>
Date: Sun, 1 Mar 2026 13:56:04 +0100
Subject: [PATCH 3/5] fixup! optimize backpressure check

---
 lib/internal/webstreams/readablestream.js | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/lib/internal/webstreams/readablestream.js b/lib/internal/webstreams/readablestream.js
index 2456d1798f158a..f163a4e3b0642c 100644
--- a/lib/internal/webstreams/readablestream.js
+++ b/lib/internal/webstreams/readablestream.js
@@ -127,7 +127,6 @@ const {
   writableStreamAbort,
   writableStreamCloseQueuedOrInFlight,
   writableStreamDefaultWriterCloseWithErrorPropagation,
-  writableStreamDefaultWriterGetDesiredSize,
   writableStreamDefaultWriterRelease,
   writableStreamDefaultWriterWrite,
 } = require('internal/webstreams/writablestream');
@@ -1564,12 +1563,12 @@ function readableStreamPipeTo(
         setPromiseHandled(state.currentWrite);
 
         // Check backpressure after each write
-        if (dest[kState].state === 'writable') {
-          const desiredSize = writableStreamDefaultWriterGetDesiredSize(writer);
-          if (desiredSize !== null && desiredSize <= 0) {
-            // Backpressure - stop batch and wait for ready
-            break;
-          }
+        if (dest[kState].backpressure) {
+          // Backpressure - stop batch and wait for ready
+          break;
+        } else if (dest[kState].state !== 'writable' || writableStreamCloseQueuedOrInFlight(dest)) {
+          // Closing or erroring - stop batch and wait for shutdown
+          break;
         }
       }
 

From 911f8958952597fdd24684010cd0a4cd95c521c8 Mon Sep 17 00:00:00 2001
From: Mattias Buelens <mattias@buelens.com>
Date: Mon, 2 Mar 2026 20:58:14 +0100
Subject: [PATCH 4/5] fixup! wait for ready only if there is backpressure

---
 lib/internal/webstreams/readablestream.js | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/internal/webstreams/readablestream.js b/lib/internal/webstreams/readablestream.js
index f163a4e3b0642c..4cc457c130009c 100644
--- a/lib/internal/webstreams/readablestream.js
+++ b/lib/internal/webstreams/readablestream.js
@@ -1532,10 +1532,12 @@ function readableStreamPipeTo(
   }
 
   async function step() {
-    if (shuttingDown)
-      return true;
+    if (shuttingDown) return true;
 
-    await writer[kState].ready.promise;
+    if (dest[kState].backpressure) {
+      await writer[kState].ready.promise;
+      if (shuttingDown) return true;
+    }
 
     const controller = source[kState].controller;
 

From 7b31401e6d9ad9f48090334272943f3b21d29508 Mon Sep 17 00:00:00 2001
From: Mattias Buelens <mattias@buelens.com>
Date: Mon, 2 Mar 2026 21:04:06 +0100
Subject: [PATCH 5/5] fixup! disturbed is already true at start of pipeTo

---
 lib/internal/webstreams/readablestream.js | 1 -
 1 file changed, 1 deletion(-)

diff --git a/lib/internal/webstreams/readablestream.js b/lib/internal/webstreams/readablestream.js
index 4cc457c130009c..69a2cc65098089 100644
--- a/lib/internal/webstreams/readablestream.js
+++ b/lib/internal/webstreams/readablestream.js
@@ -1551,7 +1551,6 @@ function readableStreamPipeTo(
       while (controller[kState].queue.length > 0) {
         if (shuttingDown) return true;
 
-        source[kState].disturbed = true;
         const chunk = dequeueValue(controller);
 
         if (controller[kState].closeRequested && !controller[kState].queue.length) {