From d7751085d4061937a7bbbc0a853bb3685e5a6d4a Mon Sep 17 00:00:00 2001
From: Erick Cestari <erickcestari03@gmail.com>
Date: Sat, 3 Oct 2026 00:02:57 -0300
Subject: [PATCH] smite: re-arm TCP_QUICKACK after each send

LDK doesn't set TCP_NODELAY, so it holds a small reply until we ACK its
last segment, and Linux delays that ACK ~40 ms. This stalled the final
pong of every LDK funding execution; fixing it takes LDK from 13.3 to
42.9 execs/s under Nyx.
---
 smite/src/noise/connection.rs | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/smite/src/noise/connection.rs b/smite/src/noise/connection.rs
index 2dd89285..7be754c0 100644
--- a/smite/src/noise/connection.rs
+++ b/smite/src/noise/connection.rs
@@ -2,6 +2,7 @@
 
 use std::io::{Read, Write};
 use std::net::{SocketAddr, TcpStream};
+use std::os::linux::net::TcpStreamExt;
 use std::time::Duration;
 
 use bitcoin::secp256k1::{PublicKey, SecretKey};
@@ -84,6 +85,7 @@ impl NoiseConnection {
         }
         let encrypted = self.cipher.encrypt(msg);
         self.stream.write_all(&encrypted)?;
+        self.stream.set_quickack(true)?;
         Ok(())
     }
 
@@ -141,3 +143,30 @@ pub enum ConnectionError {
     #[error("message too large: {0} bytes (max {max})", max = MAX_MESSAGE_SIZE)]
     MessageTooLarge(usize),
 }
+
+#[cfg(test)]
+mod tests {
+    use std::io::{Read, Write};
+    use std::net::{TcpListener, TcpStream};
+    use std::os::linux::net::TcpStreamExt;
+
+    use super::{NoiseCipher, NoiseConnection};
+
+    #[test]
+    fn send_after_read_keeps_quickack() {
+        let listener = TcpListener::bind("127.0.0.1:0").unwrap();
+        let stream = TcpStream::connect(listener.local_addr().unwrap()).unwrap();
+        let (mut peer, _) = listener.accept().unwrap();
+        let mut conn = NoiseConnection {
+            stream,
+            cipher: NoiseCipher::new([1; 32], [2; 32], [3; 32]),
+        };
+
+        // Sending right after a read is what makes Linux delay its ACKs.
+        peer.write_all(&[0]).unwrap();
+        conn.stream.read_exact(&mut [0]).unwrap();
+        conn.send_message(b"ping").unwrap();
+
+        assert!(conn.stream.quickack().unwrap());
+    }
+}