From b2aa380da10e073b1226a5c5999a8fd909b1bbbb Mon Sep 17 00:00:00 2001
From: "Kamat, Trivikram" <16024985+trivikr@users.noreply.github.com>
Date: Sun, 12 Jul 2026 17:29:53 -0700
Subject: [PATCH] stream: reject strings in ReadableStream.from

Use Web IDL async_sequence semantics for ReadableStream.from(), which
require the input to be an object. This causes primitive strings to
throw a TypeError instead of being iterated by code point.

Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com>
Assisted-by: openai:gpt-5.6-sol
---
 lib/internal/webstreams/readablestream.js              | 6 ++++++
 test/fixtures/wpt/streams/readable-streams/from.any.js | 6 +-----
 test/parallel/test-webstream-readable-from.js          | 5 +++++
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/lib/internal/webstreams/readablestream.js b/lib/internal/webstreams/readablestream.js
index d0e3bfafc19fcd..33a86b46ae430c 100644
--- a/lib/internal/webstreams/readablestream.js
+++ b/lib/internal/webstreams/readablestream.js
@@ -1448,6 +1448,12 @@ function createReadableStreamState() {
 }
 
 function readableStreamFromIterable(iterable) {
+  // Web IDL async_sequence conversion only accepts ECMAScript objects.
+  // In particular, strings must not be treated as iterable inputs here.
+  if ((typeof iterable !== 'object' || iterable === null) &&
+      typeof iterable !== 'function') {
+    throw new ERR_ARG_NOT_ITERABLE(iterable);
+  }
   let stream;
   const iteratorGetter = iterable[SymbolAsyncIterator] ?? iterable[SymbolIterator];
   if (iteratorGetter == null || typeof iteratorGetter !== 'function') {
diff --git a/test/fixtures/wpt/streams/readable-streams/from.any.js b/test/fixtures/wpt/streams/readable-streams/from.any.js
index 2b28a05fee398c..29f5472d8a69e3 100644
--- a/test/fixtures/wpt/streams/readable-streams/from.any.js
+++ b/test/fixtures/wpt/streams/readable-streams/from.any.js
@@ -18,11 +18,6 @@ const iterableFactories = [
     return ['a', 'b'][Symbol.iterator]();
   }],
 
-  ['a string', () => {
-    // This iterates over the code points of the string.
-    return 'ab';
-  }],
-
   ['a Set', () => {
     return new Set(['a', 'b']);
   }],
@@ -144,6 +139,7 @@ const badIterables = [
   ['Object.create(null)', Object.create(null)],
   ['a function', () => 42],
   ['a symbol', Symbol()],
+  ['a string', 'ab'],
   ['an object with a non-callable @@iterator method', {
     [Symbol.iterator]: 42
   }],
diff --git a/test/parallel/test-webstream-readable-from.js b/test/parallel/test-webstream-readable-from.js
index 0a0c6943c72556..599e10a8e6284e 100644
--- a/test/parallel/test-webstream-readable-from.js
+++ b/test/parallel/test-webstream-readable-from.js
@@ -8,6 +8,11 @@ assert.throws(
   { code: 'ERR_ARG_NOT_ITERABLE', name: 'TypeError' },
 );
 
+assert.throws(
+  () => ReadableStream.from('abc'),
+  { code: 'ERR_ARG_NOT_ITERABLE', name: 'TypeError' },
+);
+
 const invalidIterators = [
   { [Symbol.iterator]: () => 42 },
   { [Symbol.asyncIterator]: () => 42 },