nodejs · martenrichter · Aug 16, 2026
diff --git a/doc/api/quic.md b/doc/api/quic.md
@@ -1300,6 +1300,11 @@ added: v23.8.0
     will buffer before `writeSync()` returns `false`. When the buffered
     data exceeds this limit, the caller should wait for drain before
     writing more. **Default:** `65536` (64 KB).
+  * `waitUntilAvailable` {boolean} When true the promise will wait until flow
+    control will allow to open the stream. If set to false, the function
+    will fail synchronously, if flow control will not allow to open the stream
+    immediately.
+    **Default:** `false`
   * `onheaders` {Function} Callback for received initial response headers.
     Called with `(headers)`.
   * `ontrailers` {Function} Callback for received trailing headers.
@@ -1341,6 +1346,11 @@ added: v23.8.0
     will buffer before `writeSync()` returns `false`. When the buffered
     data exceeds this limit, the caller should wait for drain before
     writing more. **Default:** `65536` (64 KB).
+  * `waitUntilAvailable` {boolean} When true the promise will wait until flow
+    control will allow to open the stream. If set to false, the function
+    will fail synchronously, if flow control will not allow to open the stream
+    immediately.
+    **Default:** `false`
   * `onheaders` {Function} Callback for received initial response headers.
     Called with `(headers)`.
   * `ontrailers` {Function} Callback for received trailing headers.

diff --git a/lib/internal/quic/quic.js b/lib/internal/quic/quic.js
@@ -3347,6 +3347,7 @@ class QuicSession {
       incremental = false,
       budget = kDefaultBudget,
       headers,
+      waitUntilAvailable = false,
       onheaders,
       ontrailers,
       oninfo,
@@ -3358,7 +3359,7 @@ class QuicSession {
 
     const validatedBody = validateBody(body);
 
-    const handle = this.#handle.openStream(direction, validatedBody);
+    const handle = this.#handle.openStream(direction, waitUntilAvailable, validatedBody);
     if (handle === undefined) {
       throw new ERR_QUIC_OPEN_STREAM_FAILED();
     }

diff --git a/src/quic/session.cc b/src/quic/session.cc
@@ -1167,17 +1167,24 @@ struct Session::Impl final : public MemoryRetainer {
     }
 
     DCHECK(args[0]->IsUint32());
+    DCHECK(args[1]->IsBoolean());
+
+    auto direction = FromV8Value<Direction>(args[0]);
+    if (!args[1].As<v8::Boolean>()->Value() && false) { // This is waitUntilAvailable
+      if (!session->CanImmediatelyOpenStream(direction)) {
+        return THROW_ERR_INVALID_STATE(env, "No new stream available within flow control");
+      }
+    }
 
     // GetDataQueueFromSource handles type validation.
     std::shared_ptr<DataQueue> data_source;
-    if (!Stream::GetDataQueueFromSource(env, args[1]).To(&data_source))
+    if (!Stream::GetDataQueueFromSource(env, args[2]).To(&data_source))
         [[unlikely]] {
       return THROW_ERR_INVALID_ARG_VALUE(env, "Invalid data source");
     }
 
     session->impl_->handshake_deferred_ = false;
     SendPendingDataScope send_scope(session);
-    auto direction = FromV8Value<Direction>(args[0]);
     Local<Object> stream;
     if (session->OpenStream(direction, std::move(data_source)).ToLocal(&stream))
         [[likely]] {
@@ -3166,6 +3173,14 @@ BaseObjectPtr<Stream> Session::CreateStream(
   return {};
 }
 
+bool Session::CanImmediatelyOpenStream(Direction direction) {
+  if (direction == Direction::BIDIRECTIONAL) {
+    return max_local_streams_bidi() > 0;
+  } else {
+    return max_local_streams_uni() > 0;
+  }
+}
+
 MaybeLocal<Object> Session::OpenStream(Direction direction,
                                        std::shared_ptr<DataQueue> data_source) {
   // If can_create_streams() returns false, we are not able to open a stream
@@ -3507,13 +3522,12 @@ void Session::SetApplicationError(error_code app_error_code) {
 
 uint64_t Session::max_local_streams_uni() const {
   DCHECK(!is_destroyed());
-  return ngtcp2_conn_get_streams_uni_left(*this);
+  return ngtcp2_conn_get_streams_uni_left2(*this);
 }
 
 uint64_t Session::max_local_streams_bidi() const {
   DCHECK(!is_destroyed());
-  return ngtcp2_conn_get_local_transport_params(*this)
-      ->initial_max_streams_bidi;
+  return  ngtcp2_conn_get_streams_bidi_left2(*this);
 }
 
 void Session::set_wrapped() {

diff --git a/src/quic/session.h b/src/quic/session.h
@@ -522,6 +522,9 @@ class Session final : public AsyncWrap, private SessionTicket::AppData::Source {
   size_t max_packet_size() const;
   void set_priority_supported(bool on = true);
 
+  // Check whether flow control permits opening another stream
+  bool CanImmediatelyOpenStream(Direction direction);
+
   // Open a new locally-initialized stream with the specified directionality.
   // If the session is not yet in a state where the stream can be openen --
   // such as when the handshake is not yet sufficiently far along and ORTT

diff --git a/test/parallel/test-quic-stream-limits-pending.mjs b/test/parallel/test-quic-stream-limits-pending.mjs
@@ -15,22 +15,30 @@
 
 const { listen, connect } = await import('../common/quic.mjs');
 const { bytes } = await import('stream/iter');
+const { setTimeout: sleep } = await import('timers/promises');
 
 const encoder = new TextEncoder();
 const allDone = Promise.withResolvers();
+const twoDone = Promise.withResolvers();
 let serverStreamCount = 0;
 
 // Server allows only 1 bidi stream at a time.
 const serverEndpoint = await listen(mustCall((serverSession) => {
   serverSession.onstream = mustCall(async (stream) => {
-    await bytes(stream);
+    const streambytes = await bytes(stream);
     stream.writer.endSync();
     await stream.closed;
-    if (++serverStreamCount === 2) {
-      serverSession.close();
+    ++serverStreamCount;
+    if (serverStreamCount === 2) {
+      twoDone.resolve();
+    }
+    if (serverStreamCount === 3) {
       allDone.resolve();
     }
-  }, 2);
+    if (serverStreamCount === 4) {
+      serverSession.close();
+    }
+  }, 4);
 }), {
   transportParams: { initialMaxStreamsBidi: 1 },
 });
@@ -41,29 +49,50 @@
 // First stream opens immediately (within the limit).
 const s1 = await clientSession.createBidirectionalStream({
   body: encoder.encode('stream 1'),
+  waitUntilAvailable: true
 });
 
-// Second stream is created but queued as pending because the
+try {
+  // Second stream should not open, but throw.
+  const s2 = await clientSession.createBidirectionalStream({
+    body: encoder.encode('stream 2'),
+    waitUntilAvailable: false
+  });
+} catch (error) {
+  assert.strictEqual(error.code, 'ERR_INVALID_STATE');
+}
+
+// Third stream is created but queued as pending because the
 // server only allows 1 concurrent bidi stream.
-const s2 = await clientSession.createBidirectionalStream({
-  body: encoder.encode('stream 2'),
+const s3 = await clientSession.createBidirectionalStream({
+  body: encoder.encode('stream 3'),
+  waitUntilAvailable: true
 });
 
-// s2 should be pending until s1 closes and the server grants
+// s3 should be pending until s1 closes and the server grants
 // more stream credits.
-assert.strictEqual(s2.pending, true);
+assert.strictEqual(s3.pending, true);
 
 // Drain and close the first stream.
 for await (const _ of s1) { /* drain */ } // eslint-disable-line no-unused-vars
 await s1.closed;
 
-// After s1 closes, the server sends MAX_STREAMS which opens s2.
+// After s1 closes, the server sends MAX_STREAMS which opens s3.
 // Wait for the server to receive both streams.
-await allDone.promise;
+await twoDone.promise;
+// s3 should no longer be pending.
+for await (const _ of s3) { /* drain */ } // eslint-disable-line no-unused-vars
+await s3.closed;
 
-// s2 should no longer be pending.
-for await (const _ of s2) { /* drain */ } // eslint-disable-line no-unused-vars
-await s2.closed;
+await sleep(10); // we wait a bit, as we do not have a callback exposed to js
+// fourth stream should open immediately and not throw
+console.log('before last stream')
+const s4 = await clientSession.createBidirectionalStream({
+  body: encoder.encode('stream 4'),
+  waitUntilAvailable: false
+});
+await s4.closed;
+await allDone.promise;
 
 await clientSession.close();
 await serverEndpoint.close();