Accept TCP FIN packets in SYN-RECEIVED state.

examples/loopback.rs

@@ -1,6 +1,8 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 #![allow(unused_mut)]
 
+#[cfg(feature = "std")]
+use std as core;
 #[macro_use]
 extern crate log;
 extern crate smoltcp;
@@ -13,6 +15,7 @@ extern crate getopts;
 #[allow(dead_code)]
 mod utils;
 
+use core::str;
 use smoltcp::Error;
 use smoltcp::phy::Loopback;
 use smoltcp::wire::{EthernetAddress, IpAddress};
@@ -126,13 +129,14 @@ fn main() {
             let socket: &mut TcpSocket = socket_set.get_mut(server_handle).as_socket();
             if !socket.is_active() && !socket.is_listening() {
                 if !did_listen {
+                    debug!("listening");
                     socket.listen(1234).unwrap();
                     did_listen = true;
                 }
             }
 
             if socket.can_recv() {
-                debug!("got {:?}", socket.recv(32).unwrap());
+                debug!("got {:?}", str::from_utf8(socket.recv(32).unwrap()).unwrap());
                 socket.close();
                 done = true;
             }
@@ -142,6 +146,7 @@ fn main() {
             let socket: &mut TcpSocket = socket_set.get_mut(client_handle).as_socket();
             if !socket.is_open() {
                 if !did_connect {
+                    debug!("connecting");
                     socket.connect((IpAddress::v4(127, 0, 0, 1), 1234),
                                    (IpAddress::Unspecified, 65000)).unwrap();
                     did_connect = true;
@@ -149,6 +154,7 @@ fn main() {
             }
 
             if socket.can_send() {
+                debug!("sending");
                 socket.send_slice(b"0123456789abcdef").unwrap();
                 socket.close();
             }
@@ -162,7 +168,9 @@ fn main() {
         clock.advance(1);
     }
 
-    if !done {
-        error!("this is taking too long, bailing out");
+    if done {
+        info!("done")
+    } else {
+        error!("this is taking too long, bailing out")
     }
 }

src/socket/tcp.rs

@@ -852,6 +852,15 @@ impl<'a> TcpSocket<'a> {
                 self.retransmit.reset();
             }
 
+            // FIN packets in the SYN-RECEIVED state change it to CLOSE-WAIT.
+            // It's not obvious from RFC 793 that this is permitted, but
+            // 7th and 8th steps in the "SEGMENT ARRIVES" event describe this behavior.
+            (State::SynReceived, TcpRepr { control: TcpControl::Fin, .. }) => {
+                self.remote_seq_no  += 1;
+                self.set_state(State::CloseWait);
+                self.retransmit.reset();
+            }
+
             // SYN|ACK packets in the SYN-SENT state change it to ESTABLISHED.
             (State::SynSent, TcpRepr {
                 control: TcpControl::Syn, seq_number, ack_number: Some(_),
@@ -1498,7 +1507,7 @@ mod test {
     }
 
     #[test]
-    fn test_syn_received_syn_ack() {
+    fn test_syn_received_ack() {
         let mut s = socket_syn_received();
         recv!(s, [TcpRepr {
             control: TcpControl::Syn,
@@ -1516,6 +1525,30 @@ mod test {
         sanity!(s, socket_established());
     }
 
+    #[test]
+    fn test_syn_received_fin() {
+        let mut s = socket_syn_received();
+        recv!(s, [TcpRepr {
+            control: TcpControl::Syn,
+            seq_number: LOCAL_SEQ,
+            ack_number: Some(REMOTE_SEQ + 1),
+            max_seg_size: Some(1480),
+            ..RECV_TEMPL
+        }]);
+        send!(s, TcpRepr {
+            control: TcpControl::Fin,
+            seq_number: REMOTE_SEQ + 1,
+            ack_number: Some(LOCAL_SEQ + 1),
+            payload: &b"abcdef"[..],
+            ..SEND_TEMPL
+        });
+        assert_eq!(s.state, State::CloseWait);
+        sanity!(s, TcpSocket {
+            remote_last_ack: REMOTE_SEQ + 1,
+            ..socket_close_wait()
+        });
+    }
+
     #[test]
     fn test_syn_received_rst() {
         let mut s = socket_syn_received();