From f1a4db44c4c3f591df378190a6604d4547a37c25 Mon Sep 17 00:00:00 2001
From: kbleeke <pluth@0t.re>
Date: Wed, 22 Feb 2023 13:57:40 +0100
Subject: [PATCH 1/2] Implement flush for TcpSocket

---
 embassy-net/src/tcp.rs | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/embassy-net/src/tcp.rs b/embassy-net/src/tcp.rs
index d46bd4dbf..b9e494fc4 100644
--- a/embassy-net/src/tcp.rs
+++ b/embassy-net/src/tcp.rs
@@ -254,10 +254,19 @@ impl<'d> TcpIo<'d> {
         .await
     }
 
-    #[allow(unused)]
     async fn flush(&mut self) -> Result<(), Error> {
-        poll_fn(move |_| {
-            Poll::Ready(Ok(())) // TODO: Is there a better implementation for this?
+        poll_fn(move |cx| {
+            self.with_mut(|s, _| {
+                // If there are outstanding send operations, register for wake up and wait
+                // smoltcp issues wake-ups when octets are dequeued from the send buffer
+                if s.send_queue() > 0 {
+                    s.register_send_waker(cx.waker());
+                    Poll::Pending
+                // No outstanding sends, socket is flushed
+                } else {
+                    Poll::Ready(Ok(()))
+                }
+            })
         })
         .await
     }

From 035de6f3ff7bae31dce25b55e822f75b46ebe047 Mon Sep 17 00:00:00 2001
From: kbleeke <pluth@0t.re>
Date: Wed, 22 Feb 2023 14:45:17 +0100
Subject: [PATCH 2/2] embassy-net: add flush to TcpSocket and TcpWriter as an
 inherent method

---
 embassy-net/src/tcp.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/embassy-net/src/tcp.rs b/embassy-net/src/tcp.rs
index b9e494fc4..c3d8764b0 100644
--- a/embassy-net/src/tcp.rs
+++ b/embassy-net/src/tcp.rs
@@ -63,6 +63,10 @@ impl<'a> TcpWriter<'a> {
     pub async fn write(&mut self, buf: &[u8]) -> Result<usize, Error> {
         self.io.write(buf).await
     }
+
+    pub async fn flush(&mut self) -> Result<(), Error> {
+        self.io.flush().await
+    }
 }
 
 impl<'a> TcpSocket<'a> {
@@ -146,6 +150,10 @@ impl<'a> TcpSocket<'a> {
         self.io.write(buf).await
     }
 
+    pub async fn flush(&mut self) -> Result<(), Error> {
+        self.io.flush().await
+    }
+
     pub fn set_timeout(&mut self, duration: Option<Duration>) {
         self.io.with_mut(|s, _| s.set_timeout(duration))
     }