Merge #662

662: Only clear retransmit timer when all packets are acked r=Dirbaio a=SquidDev

Fixes #660.

While I've tested this on several physical devices, and can confirm they behave as expected, I'm definitely not familiar with the intricacies of smoltcp (or TCP in general!), so not sure what potential regressions there might be here. Happy to make any and all changes needed!

Co-authored-by: Jonathan Coates <jonathan.coates@oxionics.com>

src/socket/tcp.rs

@@ -1460,6 +1460,7 @@ impl<'a> Socket<'a> {
         // from the sequence space.
         let mut ack_len = 0;
         let mut ack_of_fin = false;
+        let mut ack_all = false;
         if repr.control != TcpControl::Rst {
             if let Some(ack_number) = repr.ack_number {
                 // Sequence number corresponding to the first byte in `tx_buffer`.
@@ -1477,6 +1478,8 @@ impl<'a> Socket<'a> {
                         tcp_trace!("received ACK of FIN");
                         ack_of_fin = true;
                     }
+
+                    ack_all = self.remote_last_seq == ack_number
                 }
 
                 self.rtte.on_ack(cx.now(), ack_number);
@@ -1585,7 +1588,7 @@ impl<'a> Socket<'a> {
             // ACK packets in ESTABLISHED state reset the retransmit timer,
             // except for duplicate ACK packets which preserve it.
             (State::Established, TcpControl::None) => {
-                if !self.timer.is_retransmit() || ack_len != 0 {
+                if !self.timer.is_retransmit() || ack_all {
                     self.timer.set_for_idle(cx.now(), self.keep_alive);
                 }
             }
@@ -1604,7 +1607,9 @@ impl<'a> Socket<'a> {
                 if ack_of_fin {
                     self.set_state(State::FinWait2);
                 }
-                self.timer.set_for_idle(cx.now(), self.keep_alive);
+                if ack_all {
+                    self.timer.set_for_idle(cx.now(), self.keep_alive);
+                }
             }
 
             // FIN packets in FIN-WAIT-1 state change it to CLOSING, or to TIME-WAIT
@@ -4979,6 +4984,85 @@ mod test {
         recv_nothing!(s, time 1550);
     }
 
+    #[test]
+    fn test_data_retransmit_bursts_half_ack() {
+        let mut s = socket_established();
+        s.remote_mss = 6;
+        s.send_slice(b"abcdef012345").unwrap();
+
+        recv!(s, time 0, Ok(TcpRepr {
+            control:    TcpControl::None,
+            seq_number: LOCAL_SEQ + 1,
+            ack_number: Some(REMOTE_SEQ + 1),
+            payload:    &b"abcdef"[..],
+            ..RECV_TEMPL
+        }), exact);
+        recv!(s, time 0, Ok(TcpRepr {
+            control:    TcpControl::Psh,
+            seq_number: LOCAL_SEQ + 1 + 6,
+            ack_number: Some(REMOTE_SEQ + 1),
+            payload:    &b"012345"[..],
+            ..RECV_TEMPL
+        }), exact);
+        // Acknowledge the first packet
+        send!(s, time 5, TcpRepr {
+            seq_number: REMOTE_SEQ + 1,
+            ack_number: Some(LOCAL_SEQ + 1 + 6),
+            window_len: 6,
+            ..SEND_TEMPL
+        });
+        // The second packet should be re-sent.
+        recv!(s, time 1500, Ok(TcpRepr {
+            control:    TcpControl::Psh,
+            seq_number: LOCAL_SEQ + 1 + 6,
+            ack_number: Some(REMOTE_SEQ + 1),
+            payload:    &b"012345"[..],
+            ..RECV_TEMPL
+        }), exact);
+
+        recv_nothing!(s, time 1550);
+    }
+
+    #[test]
+    fn test_data_retransmit_bursts_half_ack_close() {
+        let mut s = socket_established();
+        s.remote_mss = 6;
+        s.send_slice(b"abcdef012345").unwrap();
+        s.close();
+
+        recv!(s, time 0, Ok(TcpRepr {
+            control:    TcpControl::None,
+            seq_number: LOCAL_SEQ + 1,
+            ack_number: Some(REMOTE_SEQ + 1),
+            payload:    &b"abcdef"[..],
+            ..RECV_TEMPL
+        }), exact);
+        recv!(s, time 0, Ok(TcpRepr {
+            control:    TcpControl::Fin,
+            seq_number: LOCAL_SEQ + 1 + 6,
+            ack_number: Some(REMOTE_SEQ + 1),
+            payload:    &b"012345"[..],
+            ..RECV_TEMPL
+        }), exact);
+        // Acknowledge the first packet
+        send!(s, time 5, TcpRepr {
+            seq_number: REMOTE_SEQ + 1,
+            ack_number: Some(LOCAL_SEQ + 1 + 6),
+            window_len: 6,
+            ..SEND_TEMPL
+        });
+        // The second packet should be re-sent.
+        recv!(s, time 1500, Ok(TcpRepr {
+            control:    TcpControl::Fin,
+            seq_number: LOCAL_SEQ + 1 + 6,
+            ack_number: Some(REMOTE_SEQ + 1),
+            payload:    &b"012345"[..],
+            ..RECV_TEMPL
+        }), exact);
+
+        recv_nothing!(s, time 1550);
+    }
+
     #[test]
     fn test_send_data_after_syn_ack_retransmit() {
         let mut s = socket_syn_received();