stream: check done before backpressure in stream reader

watilde · aduh95 · commit 10272a94b627 · 2026-06-18T10:10:47.000+02:00
Signed-off-by: Daijiro Wachi <daijiro.wachi@gmail.com> PR-URL: #63699 Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
diff --git a/lib/internal/streams/compose.js b/lib/internal/streams/compose.js
@@ -204,12 +204,12 @@ module.exports = function compose(...streams) {
           try {
             const { value, done } = await reader.read();
 
-            if (!d.push(value)) {
+            if (done) {
+              d.push(null);
               return;
             }
 
-            if (done) {
-              d.push(null);
+            if (!d.push(value)) {
               return;
             }
           } catch {
diff --git a/test/parallel/test-stream-compose.js b/test/parallel/test-stream-compose.js
@@ -537,3 +537,24 @@ const assert = require('assert');
   assert.strictEqual(duplex.destroyed, true);
 
 }
+
+// Regression test: compose with a web TransformStream tail must always emit
+// null (EOF) when the source finishes. The done check must precede the
+// backpressure check in the reader.read() loop; otherwise push(null) can be
+// skipped if canPushMore() returns false on the final done:true read.
+{
+  const { TransformStream } = globalThis;
+  const { Readable } = require('stream');
+
+  // A web TransformStream as the tail exercises the isWebStream code path
+  // in compose that loops over reader.read() results.
+  const ts = new TransformStream();
+  const src = Readable.from(['hello', ' ', 'world']);
+  const composed = compose(src, ts);
+
+  let result = '';
+  composed.on('data', (chunk) => { result += Buffer.from(chunk).toString(); });
+  composed.on('end', common.mustCall(() => {
+    assert.strictEqual(result, 'hello world');
+  }));
+}

Original file line number	Diff line number	Diff line change
`@@ -204,12 +204,12 @@ module.exports = function compose(...streams) {`
`204`	`204`	`try {`
`205`	`205`	`const { value, done } = await reader.read();`
`206`	`206`
`207`		`- if (!d.push(value)) {`
	`207`	`+ if (done) {`
	`208`	`+ d.push(null);`
`208`	`209`	`return;`
`209`	`210`	`}`
`210`	`211`
`211`		`- if (done) {`
`212`		`- d.push(null);`
	`212`	`+ if (!d.push(value)) {`
`213`	`213`	`return;`
`214`	`214`	`}`
`215`	`215`	`} catch {`