From af9376300907dd187e0fdca793ccda2fa62de5ec Mon Sep 17 00:00:00 2001
From: Minh Vu <vuhoangminh97@gmail.com>
Date: Mon, 10 Aug 2026 12:19:30 +0200
Subject: [PATCH] io: handle empty vectored writes in simplex (#8353)

---
 tokio-util/src/io/simplex.rs   |  4 ++++
 tokio-util/tests/io_simplex.rs | 13 +++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/tokio-util/src/io/simplex.rs b/tokio-util/src/io/simplex.rs
index 5aaf44e0d..39f4222de 100644
--- a/tokio-util/src/io/simplex.rs
+++ b/tokio-util/src/io/simplex.rs
@@ -291,6 +291,10 @@ impl AsyncWrite for Sender {
             return Poll::Ready(Err(IoError::new(IoErrorKind::BrokenPipe, CLOSED_ERROR_MSG)));
         }
 
+        if bufs.iter().all(|buf| buf.is_empty()) {
+            return Poll::Ready(Ok(0));
+        }
+
         let free = inner
             .backpressure_boundary
             .checked_sub(inner.buf.len())
diff --git a/tokio-util/tests/io_simplex.rs b/tokio-util/tests/io_simplex.rs
index 0b54b7986..f541a7133 100644
--- a/tokio-util/tests/io_simplex.rs
+++ b/tokio-util/tests/io_simplex.rs
@@ -354,3 +354,16 @@ async fn poll_write_vectored_3() {
     let n = assert_ready!(tx.poll_write_vectored(&mut noop_context(), io_slices)).unwrap();
     assert_eq!(n, 0);
 }
+
+/// The `Sender::poll_write_vectored` should return `Poll::Ready(Ok(0))`
+/// if all the input buffers have zero length, even when the channel is full.
+#[tokio::test]
+async fn poll_write_vectored_4() {
+    let (mut tx, _rx) = simplex::new(1);
+    tx.write_all(&[1]).await.unwrap();
+
+    let io_slices = &[IoSlice::new(&[]), IoSlice::new(&[])];
+    tokio::pin!(tx);
+    let n = assert_ready!(tx.poll_write_vectored(&mut noop_context(), io_slices)).unwrap();
+    assert_eq!(n, 0);
+}