stream: reject strings in ReadableStream.from

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') {

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
   }],

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 },