stream: flush each fused stateless transform

trivikr · aduh95 · commit 4f40a85a1a96 · 2026-05-27T11:35:45.000+02:00
Ensure consecutive stateless stream/iter transforms each receive a final null flush after upstream flush output has been processed. Fixes: #63467 Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: openai:gpt-5.5 PR-URL: #63468 Fixes: #63467 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>
diff --git a/lib/internal/streams/iter/pull.js b/lib/internal/streams/iter/pull.js
@@ -273,6 +273,17 @@ function* processTransformResultSync(result) {
     result);
 }
 
+/**
+ * Append normalized transform result batches to an array (sync).
+ * @param {Array<Uint8Array[]>} target
+ * @param {*} result
+ */
+function appendTransformResultSync(target, result) {
+  for (const batch of processTransformResultSync(result)) {
+    ArrayPrototypePush(target, batch);
+  }
+}
+
 /**
  * Process transform result (async).
  * @yields {Uint8Array[]}
@@ -356,6 +367,18 @@ async function* processTransformResultAsync(result) {
     result);
 }
 
+/**
+ * Append normalized transform result batches to an array (async).
+ * @param {Array<Uint8Array[]>} target
+ * @param {*} result
+ * @returns {Promise<void>}
+ */
+async function appendTransformResultAsync(target, result) {
+  for await (const batch of processTransformResultAsync(result)) {
+    ArrayPrototypePush(target, batch);
+  }
+}
+
 // =============================================================================
 // Sync Pipeline Implementation
 // =============================================================================
@@ -398,18 +421,19 @@ function* applyFusedStatelessSyncTransforms(source, run) {
       yield* processTransformResultSync(current);
     }
   }
-  // Flush
-  let current = null;
+  // Flush each transform after all upstream data, including data emitted by
+  // earlier flushes, has been processed by that transform.
+  let pending = [];
   for (let i = 0; i < run.length; i++) {
-    const result = run[i](current);
-    if (result === null) {
-      current = null;
-      continue;
+    const next = [];
+    for (let j = 0; j < pending.length; j++) {
+      appendTransformResultSync(next, run[i](pending[j]));
     }
-    current = result;
+    appendTransformResultSync(next, run[i](null));
+    pending = next;
   }
-  if (current != null) {
-    yield* processTransformResultSync(current);
+  for (let i = 0; i < pending.length; i++) {
+    yield pending[i];
   }
 }
 
@@ -522,30 +546,23 @@ async function* applyFusedStatelessAsyncTransforms(source, run, signal) {
       yield* processTransformResultAsync(current);
     }
   }
-  // Flush: send null through each transform in order
-  let current = null;
+  // Flush each transform after all upstream data, including data emitted by
+  // earlier flushes, has been processed by that transform.
+  let pending = [];
   for (let i = 0; i < run.length; i++) {
-    const result = run[i](current, { __proto__: null, signal });
-    if (result === null) {
-      current = null;
-      continue;
-    }
-    if (isPromise(result)) {
-      current = await result;
-    } else {
-      current = result;
+    const next = [];
+    for (let j = 0; j < pending.length; j++) {
+      await appendTransformResultAsync(
+        next,
+        run[i](pending[j], { __proto__: null, signal }));
     }
+    await appendTransformResultAsync(
+      next,
+      run[i](null, { __proto__: null, signal }));
+    pending = next;
   }
-  if (current !== null) {
-    if (isUint8ArrayBatch(current)) {
-      if (current.length > 0) yield current;
-    } else if (isUint8Array(current)) {
-      yield [current];
-    } else if (typeof current === 'string') {
-      yield [toUint8Array(current)];
-    } else {
-      yield* processTransformResultAsync(current);
-    }
+  for (let i = 0; i < pending.length; i++) {
+    yield pending[i];
   }
 }
 
diff --git a/test/parallel/test-stream-iter-pull-async.js b/test/parallel/test-stream-iter-pull-async.js
@@ -233,6 +233,19 @@ async function testPullStatelessTransformFlush() {
   assert.strictEqual(data, 'data-TRAILER');
 }
 
+// Consecutive stateless transforms each receive a final flush signal after
+// upstream flush output has been processed.
+async function testPullConsecutiveStatelessTransformFlush() {
+  const enc = new TextEncoder();
+  const addAOnFlush = (chunks) => (chunks === null ?
+    [enc.encode('-A')] : chunks);
+  const addBOnFlush = (chunks) => (chunks === null ?
+    [enc.encode('-B')] : chunks);
+
+  const data = await text(pull(from('x'), addAOnFlush, addBOnFlush));
+  assert.strictEqual(data, 'x-A-B');
+}
+
 // Stateless transform flush error propagates
 async function testPullStatelessTransformFlushError() {
   const badFlush = (chunks) => {
@@ -357,6 +370,7 @@ async function testTransformOptionsNotShared() {
     testPullStatelessTransformError(),
     testPullStatefulTransformError(),
     testPullStatelessTransformFlush(),
+    testPullConsecutiveStatelessTransformFlush(),
     testPullStatelessTransformFlushError(),
     testPullWithSyncSource(),
     testPullStringSource(),
diff --git a/test/parallel/test-stream-iter-pull-sync.js b/test/parallel/test-stream-iter-pull-sync.js
@@ -127,6 +127,20 @@ function testPullSyncStatelessTransformFlush() {
   assert.strictEqual(data, 'data-TRAILER');
 }
 
+// Consecutive stateless transforms each receive a final flush signal after
+// upstream flush output has been processed.
+function testPullSyncConsecutiveStatelessTransformFlush() {
+  const enc = new TextEncoder();
+  const addAOnFlush = (chunks) => (chunks === null ?
+    [enc.encode('-A')] : chunks);
+  const addBOnFlush = (chunks) => (chunks === null ?
+    [enc.encode('-B')] : chunks);
+
+  const data = new TextDecoder().decode(bytesSync(
+    pullSync(fromSync('x'), addAOnFlush, addBOnFlush)));
+  assert.strictEqual(data, 'x-A-B');
+}
+
 // Stateless transform flush error propagates
 function testPullSyncStatelessTransformFlushError() {
   const badFlush = (chunks) => {
@@ -173,6 +187,7 @@ Promise.all([
   testPullSyncStatelessTransformError(),
   testPullSyncStatefulTransformError(),
   testPullSyncStatelessTransformFlush(),
+  testPullSyncConsecutiveStatelessTransformFlush(),
   testPullSyncStatelessTransformFlushError(),
   testPullSyncInvalidTransform(),
 ]).then(common.mustCall());
