From 1ed237919bdafe89ec24c40df2d621035d5ae1a9 Mon Sep 17 00:00:00 2001
From: "Kamat, Trivikram" <16024985+trivikr@users.noreply.github.com>
Date: Sat, 11 Jul 2026 22:12:57 -0700
Subject: [PATCH 1/3] stream: abort pending single-source merge reads

Make the single-source merge path abort-aware so signal cancellation
rejects a pending read and closes the active source iterator.

Handle synchronous iterator return values when marking aborted cleanup
as handled.

Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com>
---
 lib/internal/streams/iter/consumers.js        |  6 ++--
 lib/internal/streams/iter/utils.js            |  2 +-
 .../test-stream-iter-consumers-merge.js       | 31 +++++++++++++++++++
 3 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/lib/internal/streams/iter/consumers.js b/lib/internal/streams/iter/consumers.js
index 8e18c1b5b930ea..3894b3fa24a8c4 100644
--- a/lib/internal/streams/iter/consumers.js
+++ b/lib/internal/streams/iter/consumers.js
@@ -426,8 +426,10 @@ function merge(...args) {
       if (normalized.length === 0) return;
 
       if (normalized.length === 1) {
-        for await (const batch of normalized[0]) {
-          signal?.throwIfAborted();
+        const source = signal !== undefined && isAsyncIterable(sources[0]) ?
+          from(yieldAbortable(sources[0], signal)) :
+          yieldAbortable(normalized[0], signal);
+        for await (const batch of source) {
           yield batch;
         }
         return;
diff --git a/lib/internal/streams/iter/utils.js b/lib/internal/streams/iter/utils.js
index ec02eca43f3385..e3ad2d0ca229b7 100644
--- a/lib/internal/streams/iter/utils.js
+++ b/lib/internal/streams/iter/utils.js
@@ -142,7 +142,7 @@ function yieldAbortable(source, signal) {
         if (!completed && typeof iterator.return === 'function') {
           const result = iterator.return();
           if (aborted) {
-            markPromiseAsHandled(result);
+            markPromiseAsHandled(PromiseResolve(result));
           } else {
             await result;
           }
diff --git a/test/parallel/test-stream-iter-consumers-merge.js b/test/parallel/test-stream-iter-consumers-merge.js
index 859fcf8c1580fa..f0be32c2e52a54 100644
--- a/test/parallel/test-stream-iter-consumers-merge.js
+++ b/test/parallel/test-stream-iter-consumers-merge.js
@@ -170,6 +170,36 @@ async function testMergeSignalDuringPendingMultiSourceRead() {
   await assert.rejects(next, { name: 'AbortError' });
 }
 
+async function testMergeSignalDuringPendingSingleSourceRead() {
+  const ac = new AbortController();
+  let returned = false;
+  const source = {
+    __proto__: null,
+    [Symbol.asyncIterator]() {
+      return this;
+    },
+    next() {
+      return new Promise(() => {});
+    },
+    return() {
+      returned = true;
+      return { __proto__: null, done: true };
+    },
+  };
+
+  const iter = merge(source, {
+    __proto__: null,
+    signal: ac.signal,
+  })[Symbol.asyncIterator]();
+
+  const next = iter.next();
+  await new Promise(setImmediate);
+  ac.abort();
+
+  await assert.rejects(next, { name: 'AbortError' });
+  assert.strictEqual(returned, true);
+}
+
 async function testMergeDoesNotDrainSourcesWhileIdle() {
   function source(n) {
     return {
@@ -332,6 +362,7 @@ Promise.all([
   testMergeConsumerBreak(),
   testMergeSignalMidIteration(),
   testMergeSignalDuringPendingMultiSourceRead(),
+  testMergeSignalDuringPendingSingleSourceRead(),
   testMergeDoesNotDrainSourcesWhileIdle(),
   testMergeStringSources(),
   testMergeObjectLikeSources(),

From 62c9f4f2a691b8e0c551571b61cf8271d883d790 Mon Sep 17 00:00:00 2001
From: "Kamat, Trivikram" <16024985+trivikr@users.noreply.github.com>
Date: Sun, 12 Jul 2026 09:26:37 -0700
Subject: [PATCH 2/3] fixup! stream: explain handling of rejecting iterator
 return thenables

---
 lib/internal/streams/iter/utils.js | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/internal/streams/iter/utils.js b/lib/internal/streams/iter/utils.js
index e3ad2d0ca229b7..c86f317f490015 100644
--- a/lib/internal/streams/iter/utils.js
+++ b/lib/internal/streams/iter/utils.js
@@ -142,6 +142,9 @@ function yieldAbortable(source, signal) {
         if (!completed && typeof iterator.return === 'function') {
           const result = iterator.return();
           if (aborted) {
+            // PromiseResolve(result) can reject if result is a thenable that
+            // rejects, so mark it as handled even though the abort takes
+            // precedence over the result of iterator.return().
             markPromiseAsHandled(PromiseResolve(result));
           } else {
             await result;

From 1ee6017dda72d4c6bcab0788fc5043ea2aa14d13 Mon Sep 17 00:00:00 2001
From: "Kamat, Trivikram" <16024985+trivikr@users.noreply.github.com>
Date: Sun, 12 Jul 2026 09:28:49 -0700
Subject: [PATCH 3/3] fixup! test: explain intentionally pending promise in
 stream merge test

---
 test/parallel/test-stream-iter-consumers-merge.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/test/parallel/test-stream-iter-consumers-merge.js b/test/parallel/test-stream-iter-consumers-merge.js
index f0be32c2e52a54..84aeb24b615915 100644
--- a/test/parallel/test-stream-iter-consumers-merge.js
+++ b/test/parallel/test-stream-iter-consumers-merge.js
@@ -179,6 +179,7 @@ async function testMergeSignalDuringPendingSingleSourceRead() {
       return this;
     },
     next() {
+      // Intentionally never settle to verify that aborting interrupts a pending read.
       return new Promise(() => {});
     },
     return() {