stream: fix ERR_INVALID_STATE when cancelling Readable.toWeb()

When a web ReadableStream returned by Readable.toWeb() is cancelled
while the underlying Readable is actively producing data, a pending
onData callback can still fire after the controller has been closed
and attempt to enqueue a chunk, throwing ERR_INVALID_STATE.

Check wasCanceled in the onData handler and return early to avoid
calling controller.enqueue() on a closed controller.

Refs: #54205

Author: richardscarrott

lib/internal/webstreams/adapters.js

@@ -507,6 +507,7 @@ function newReadableStreamFromStreamReadable(streamReadable, options = kEmptyObj
   let wasCanceled = false;
 
   function onData(chunk) {
+    if (wasCanceled) return;
     // Copy the Buffer to detach it from the pool.
     if (Buffer.isBuffer(chunk) && !objectMode)
       chunk = new Uint8Array(chunk);

test/parallel/test-stream-readable-to-web-termination.js

@@ -10,3 +10,25 @@ const { Readable } = require('stream');
   const reader = Readable.toWeb(r).getReader();
   reader.read();
 }
+
+// Cancelling a web ReadableStream while the underlying Readable is actively
+// producing data should not throw ERR_INVALID_STATE. The onData handler in
+// newReadableStreamFromStreamReadable must check wasCanceled before calling
+// controller.enqueue(). See: https://github.com/nodejs/node/issues/54205
+{
+  const readable = new Readable({
+    read() {
+      this.push(Buffer.alloc(1024));
+    },
+  });
+
+  const webStream = Readable.toWeb(readable);
+  const reader = webStream.getReader();
+
+  (async () => {
+    await reader.read();
+    await reader.read();
+    reader.releaseLock();
+    await webStream.cancel();
+  })();
+}