[inetstack] Bug Fix: Simultaneous close misses FIN resend

network_simulator/input/tcp/close/close-local.pkt

@@ -25,10 +25,11 @@
 
 // Receive FIN segment.
 +.1 TCP < F. seq 2001(0) ack 65537 win 65535 <nop>
+// Send ACK on FIN segment.
++.0 TCP > . seq 65537(0) ack 2002 win 65534 <nop>
+
 
 // Succeed to close connection immediately because we have linger set to 0.
 +0 wait(500, ...) = 0
 
-// Send ACK on FIN segment.
-+.0 TCP > . seq 65537(0) ack 2002 win 65534 <nop>
 

network_simulator/input/tcp/close/close-simultaneous.pkt

@@ -1,4 +1,4 @@
-// Tests for simultaneous close.
+// Tests for simultaneous close. This is Figure 14 of RFC 793.
 
 // Establish a connection.
 +.0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 500
@@ -18,14 +18,17 @@
 // Close connection.
 +.2 close(500) = 0
 
-// Send FIN segment.
+// Send FIN segment. Should move to FINWAIT-1
 +.0 TCP > F. seq 65536(0) ack 101 win 65535 <nop>
-// Receive ACK on FIN segment.
-+.1 TCP < F. seq 101(0) ack 65537 win 65535 <nop>
 
-// Succeed to close connection immediately because we have linger set to 0.
-+0 wait(500, ...) = 0
+// Receive FIN but no ack on FIN. Should move to Closing.
++.1 TCP < F. seq 101(0) ack 65536 win 65535 <nop>
+
+// Resend FIN on simultaneous FIN segment with FIN ack.
++.0 TCP > F. seq 65536(0) ack 102 win 65534 <nop>
 
-// Send ACK on FIN segment.
-+.0 TCP > . seq 65537(0) ack 102 win 65534 <nop>
+// Receive ACK on FIN segment. Should move to TIME WAIT
++.1 TCP < . seq 102(0) ack 65537 win 65534 <nop>
 
+// Succeed to close connection immediately because we have linger set to 0.
++0 wait(500, ...) = 0

src/rust/inetstack/protocols/layer4/tcp/established/mod.rs

@@ -35,13 +35,12 @@ use crate::{
         SharedDemiRuntime, SharedObject,
     },
 };
-use ::futures::pin_mut;
-use ::futures::FutureExt;
+use ::futures::{join, pin_mut, FutureExt};
 use ::std::{
     net::SocketAddrV4,
     ops::{Deref, DerefMut},
-    time::Duration,
-    time::Instant,
+    pin::pin,
+    time::{Duration, Instant},
 };
 
 //======================================================================================================================
@@ -206,19 +205,17 @@ impl SharedEstablishedSocket {
     async fn local_close(&mut self) -> Result<(), Fail> {
         // 1. Start close protocol by setting state and sending FIN.
         self.cb.state = State::FinWait1;
-        Sender::push_fin_and_wait_for_ack(&mut self.cb).await?;
-
-        // 2. Got ACK to our FIN. Check if we also received a FIN from remote in the meantime.
-        let state: State = self.cb.state;
-        match state {
-            State::FinWait1 => {
-                self.cb.state = State::FinWait2;
-                // Haven't received a FIN yet from remote, so wait.
-                self.cb.receiver.wait_for_fin().await?;
-            },
-            State::Closing => self.cb.state = State::TimeWait,
-            state => unreachable!("Cannot be in any other state at this point: {:?}", state),
-        };
+        Sender::push_fin(&mut self.cb)?;
+
+        // 2. Wait for FIN and FIN ack.
+        let mut me2: SharedEstablishedSocket = self.clone();
+        let mut me3: SharedEstablishedSocket = self.clone();
+        let wait_for_fin = pin!(me3.cb.receiver.wait_for_fin().fuse());
+        let wait_for_fin_ack = pin!(Sender::wait_for_fin_ack(&mut me2.cb).fuse());
+        let (result1, result2) = join!(wait_for_fin, wait_for_fin_ack);
+        result1?;
+        result2?;
+
         // 3. TIMED_WAIT
         debug_assert_eq!(self.cb.state, State::TimeWait);
         trace!("socket options: {:?}", self.cb.socket_options.get_linger());
@@ -232,8 +229,10 @@ impl SharedEstablishedSocket {
         // 0. Move state forward
         self.cb.state = State::LastAck;
         // 1. Send FIN and wait for ack before closing.
-        Sender::push_fin_and_wait_for_ack(&mut self.cb).await?;
-        self.cb.state = State::Closed;
+        Sender::push_fin(&mut self.cb)?;
+        Sender::wait_for_fin_ack(&mut self.cb).await?;
+        debug_assert_eq!(self.cb.state, State::Closed);
+
         Ok(())
     }