stream: fix Writable.toWeb() hang on synchronous drain

A race condition in the Writable.toWeb() adapter caused the stream
to hang if the underlying Node.js Writable emitted a 'drain' event
synchronously during a write() call. This often happened when
highWaterMark was set to 0.
By checking writableNeedDrain immediately after a backpressured write,
the adapter now correctly detects if the stream has already drained,
resolving the backpressure promise instead of waiting indefinitely
for an event that has already occurred.
Fixes: #61145
Signed-off-by: sangwook <rewq5991@gmail.com>
PR-URL: #61197
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: Han5991

lib/internal/webstreams/adapters.js

@@ -232,6 +232,9 @@ function newWritableStreamFromStreamWritable(streamWritable, options = kEmptyObj
 }
 if(streamWritable.writableNeedDrain||!streamWritable.write(chunk)){
 backpressurePromise=PromiseWithResolvers();
+if(!streamWritable.writableNeedDrain){
+backpressurePromise.resolve();
+}
 returnSafePromisePrototypeFinally(
 backpressurePromise.promise,()=>{
 backpressurePromise=undefined;

test/parallel/test-whatwg-webstreams-adapters-to-writablestream.js

@@ -197,3 +197,26 @@ class TestWritable extends Writable {
 assert.strictEqual(chunk,arrayBuffer);
 }));
 }
+
+{
+// Test that the stream doesn't hang when the underlying Writable
+// emits 'drain' synchronously during write().
+// Fixes: https://github.com/nodejs/node/issues/61145
+constwritable=newWritable({
+write(chunk,encoding,callback){
+callback();
+},
+});
+
+// Force synchronous 'drain' emission during write()
+// to simulate a stream that doesn't have Node.js's built-in kSync protection.
+writable.write=function(chunk){
+this.emit('drain');
+returnfalse;
+};
+
+constwritableStream=newWritableStreamFromStreamWritable(writable);
+constwriter=writableStream.getWriter();
+writer.write(newUint8Array([1,2,3])).then(common.mustCall());
+writer.write(newUint8Array([4,5,6])).then(common.mustCall());
+}