From d75daf977608325d19a5745a42705ba3391d0b20 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Kr=C3=B6ning?=
 <martin.kroening@eonerc.rwth-aachen.de>
Date: Thu, 4 Sep 2025 10:44:24 +0200
Subject: [PATCH] feat(async-io): make async `Write::flush` a required method

---
 embedded-io-async/src/impls/slice_mut.rs | 5 +++++
 embedded-io-async/src/impls/vec.rs       | 5 +++++
 embedded-io-async/src/lib.rs             | 4 +---
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/embedded-io-async/src/impls/slice_mut.rs b/embedded-io-async/src/impls/slice_mut.rs
index fbbed187..a0800cd8 100644
--- a/embedded-io-async/src/impls/slice_mut.rs
+++ b/embedded-io-async/src/impls/slice_mut.rs
@@ -25,6 +25,11 @@ impl Write for &mut [u8] {
         Ok(amt)
     }
 
+    #[inline]
+    async fn flush(&mut self) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
     #[inline]
     async fn write_all(&mut self, buf: &[u8]) -> Result<(), Self::Error> {
         if self.len() < buf.len() {
diff --git a/embedded-io-async/src/impls/vec.rs b/embedded-io-async/src/impls/vec.rs
index a9741f1e..d8aba558 100644
--- a/embedded-io-async/src/impls/vec.rs
+++ b/embedded-io-async/src/impls/vec.rs
@@ -10,6 +10,11 @@ impl Write for Vec<u8> {
         Ok(buf.len())
     }
 
+    #[inline]
+    async fn flush(&mut self) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
     #[inline]
     async fn write_all(&mut self, buf: &[u8]) -> Result<(), Self::Error> {
         self.write(buf).await?;
diff --git a/embedded-io-async/src/lib.rs b/embedded-io-async/src/lib.rs
index 1a8dbf7e..a421e54c 100644
--- a/embedded-io-async/src/lib.rs
+++ b/embedded-io-async/src/lib.rs
@@ -127,9 +127,7 @@ pub trait Write: ErrorType {
     async fn write(&mut self, buf: &[u8]) -> Result<usize, Self::Error>;
 
     /// Flush this output stream, ensuring that all intermediately buffered contents reach their destination.
-    async fn flush(&mut self) -> Result<(), Self::Error> {
-        Ok(())
-    }
+    async fn flush(&mut self) -> Result<(), Self::Error>;
 
     /// Write an entire buffer into this writer.
     ///