pseudotcp: Add optional FIN–ACK and RST support

In order to detect cases where the peer closes its connection without an
explicit in-band close message (e.g. in protocols such as Telnet where
there is none), pseudo-TCP needs to grow support for a shutdown
handshake, following the TCP FIN–ACK specification. Arguably it should
have had this all along, but Jingle apparently doesn’t need it.

This adds support for FIN–ACK to the pseudo-TCP implementation. It is
backwards-compatible, only being used if the TCP_OPT_FIN_ACK option is
specified in the SYN segment.

If enabled, full-duplex closes are supported, and the standard method
for notifying a peer of the other end closing its connection (returning
0 from recv()) is used.

Also allow rapidly tearing down a connection, discarding unsent and
unreceived data, by sending an RST segment. This preserves the ability to
do a forced socket closure with pseudo_tcp_socket_close(sock, TRUE).

It also permits graceful socket shutdown in the case where the final ACK
is lost, and one peer gets stuck in the LAST-ACK state: that peer will
eventually re-transmit its FIN segment. The other peer, in the CLOSED
state, will respond with a RST segment, and the first peer will then
reach CLOSED.

References (most useful first):
 • http://tools.ietf.org/html/rfc793#section-3.5
 • http://tools.ietf.org/html/rfc1122#page-87
 • http://vincent.bernat.im/en/blog/2014-tcp-time-wait-state-linux.html
 • http://tools.ietf.org/html/rfc675
Diagram:
 •
http://en.wikipedia.org/wiki/Transmission_Control_Protocol#mediaviewer/File:TCP_CLOSE.svg

1 files changed, 2 insertions, 0 deletions

diff --git a/tests/test-pseudotcp.c b/tests/test-pseudotcp.c
index 1044a08..e4dd613 100644
--- a/tests/test-pseudotcp.c
+++ b/tests/test-pseudotcp.c
@@ -138,6 +138,8 @@ static void readable (PseudoTcpSocket *sock, gpointer data)
           exit (-1);
         }
       }
+    } else if (len == 0) {
+      pseudo_tcp_socket_close (sock, FALSE);
     }
   } while (len > 0);