stream: fix readable stream as async iterator function

Since v19.2 it's not possible to use readableStreams
as async iterators (confirmed bug).
This patch fixes the problem by reading the Stream.Duplex property
from 'streams/duplex' instead of 'streams/legacy' module

Fixes: #46141

lib/internal/streams/readable.js

@@ -41,6 +41,7 @@ Readable.ReadableState = ReadableState;
 const EE = require('events');
 const { Stream, prependListener } = require('internal/streams/legacy');
 const { Buffer } = require('buffer');
+const Duplex = require('internal/streams/duplex');
 
 const {
   addAbortSignal,
@@ -87,7 +88,7 @@ function ReadableState(options, stream, isDuplex) {
   // values for the readable and the writable sides of the duplex stream.
   // These options can be provided separately as readableXXX and writableXXX.
   if (typeof isDuplex !== 'boolean')
-    isDuplex = stream instanceof Stream.Duplex;
+    isDuplex = stream instanceof Duplex;
 
   // Object stream flag. Used to make read(n) ignore n and to
   // make all the buffer merging and length checks go away.
@@ -189,7 +190,7 @@ function Readable(options) {
 
   // Checking for a Stream.Duplex instance is faster here instead of inside
   // the ReadableState constructor, at least with V8 6.5.
-  const isDuplex = this instanceof Stream.Duplex;
+  const isDuplex = this instanceof Duplex;
 
   this._readableState = new ReadableState(options, this, isDuplex);
 

lib/internal/streams/writable.js

@@ -42,6 +42,7 @@ Writable.WritableState = WritableState;
 
 const EE = require('events');
 const Stream = require('internal/streams/legacy').Stream;
+const Duplex = require('internal/streams/duplex');
 const { Buffer } = require('buffer');
 const destroyImpl = require('internal/streams/destroy');
 
@@ -81,7 +82,7 @@ function WritableState(options, stream, isDuplex) {
   // values for the readable and the writable sides of the duplex stream,
   // e.g. options.readableObjectMode vs. options.writableObjectMode, etc.
   if (typeof isDuplex !== 'boolean')
-    isDuplex = stream instanceof Stream.Duplex;
+    isDuplex = stream instanceof Duplex;
 
   // Object stream flag to indicate whether or not this stream
   // contains buffers or objects.
@@ -228,7 +229,7 @@ function Writable(options) {
 
   // Checking for a Stream.Duplex instance is faster here instead of inside
   // the WritableState constructor, at least with V8 6.5.
-  const isDuplex = (this instanceof Stream.Duplex);
+  const isDuplex = (this instanceof Duplex);
 
   if (!isDuplex && !FunctionPrototypeSymbolHasInstance(Writable, this))
     return new Writable(options);

test/parallel/test-stream3-pipeline-async-iterator.js

@@ -0,0 +1,27 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const { pipeline } = require('node:stream/promises');
+
+{
+  // Ensure that async iterators can act as readable and writable streams
+  async function* myCustomReadable() {
+    yield 'Hello';
+    yield 'World';
+  }
+
+  // eslint-disable-next-line require-yield
+  async function* myCustomWritable(stream) {
+    const messages = [];
+    for await (const chunk of stream) {
+      messages.push(chunk);
+    }
+    assert.deepStrictEqual(messages, ['Hello', 'World']);
+  }
+
+  pipeline(
+    myCustomReadable,
+    myCustomWritable,
+  )
+  .then(common.mustCall());
+}