$OpenBSD: nchan2.ms,v 1.4 2008/05/15 23:52:24 djm Exp $

Copyright (c) 2000 Markus Friedl. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

OpenSSH Channel Close Protocol 2.0 Implementation Channel Input State Diagram

S reset l=1 s=1.2 ellipsewid=s*ellipsewid boxwid=s*boxwid ellipseht=s*ellipseht S1: ellipse "INPUT" "OPEN" move right 2*l from last ellipse.e S3: ellipse invis move down l from last ellipse.s S4: ellipse "INPUT" "CLOSED" move down l from 1st ellipse.s S2: ellipse "INPUT" "WAIT" "DRAIN" arrow from S1.e to S4.n box invis "rcvd CLOSE/" "shutdown_read" with .sw at last arrow.c arrow "ibuf_empty ||" "rcvd CLOSE/" "send EOF" "" from S2.e to S4.w arrow from S1.s to S2.n box invis "read_failed ||" "rcvd EOW/" "shutdown_read" with .e at last arrow.c ellipse wid .9*ellipsewid ht .9*ellipseht at S4 arrow "start" "" from S1.w+(-0.5,0) to S1.w

E

Channel Output State Diagram

S S1: ellipse "OUTPUT" "OPEN" move right 2*l from last ellipse.e S3: ellipse invis move down l from last ellipse.s S4: ellipse "OUTPUT" "CLOSED" move down l from 1st ellipse.s S2: ellipse "OUTPUT" "WAIT" "DRAIN" arrow from S1.e to S4.n box invis "write_failed/" "shutdown_write" "send EOW" with .sw at last arrow.c arrow "obuf_empty ||" "write_failed/" "shutdown_write" "" from S2.e to S4.w arrow from S1.s to S2.n box invis "rcvd EOF ||" "rcvd CLOSE/" "-" with .e at last arrow.c ellipse wid .9*ellipsewid ht .9*ellipseht at S4 arrow "start" "" from S1.w+(-0.5,0) to S1.w

E

Notes

The input buffer is filled with data from the socket (the socket represents the local consumer/producer of the forwarded channel). The data is then sent over the INPUT-end (transmit-end) of the channel to the remote peer. Data sent by the peer is received on the OUTPUT-end (receive-end), saved in the output buffer and written to the socket.

If the local protocol instance has forwarded all data on the INPUT-end of the channel, it sends an EOF message to the peer.

A CLOSE message is sent to the peer if both the INPUT- and the OUTOUT-half of the local end of the channel are closed.

The channel can be deallocated by a protocol instance if a CLOSE message he been both sent and received.