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.\" $OpenBSD: nchan.ms,v 1.8 2003/11/21 11:57:03 djm Exp $
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.\" Copyright (c) 1999 Markus Friedl. All rights reserved.
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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OpenSSH Channel Close Protocol 1.5 Implementation
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Channel Input State Diagram
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ellipsewid=s*ellipsewid
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S1: ellipse "INPUT" "OPEN"
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move right 2*l from last ellipse.e
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S4: ellipse "INPUT" "CLOSED"
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move down l from last ellipse.s
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S3: ellipse "INPUT" "WAIT" "OCLOSED"
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move down l from 1st ellipse.s
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S2: ellipse "INPUT" "WAIT" "DRAIN"
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arrow "" "rcvd OCLOSE/" "shutdown_read" "send IEOF" from S1.e to S4.w
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arrow "ibuf_empty/" "send IEOF" from S2.e to S3.w
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arrow from S1.s to S2.n
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box invis "read_failed/" "shutdown_read" with .e at last arrow.c
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arrow from S3.n to S4.s
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box invis "rcvd OCLOSE/" "-" with .w at last arrow.c
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ellipse wid .9*ellipsewid ht .9*ellipseht at S4
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arrow "start" "" from S1.w+(-0.5,0) to S1.w
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arrow from S2.ne to S4.sw
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box invis "rcvd OCLOSE/ " with .e at last arrow.c
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box invis " send IEOF" with .w at last arrow.c
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Channel Output State Diagram
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S1: ellipse "OUTPUT" "OPEN"
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move right 2*l from last ellipse.e
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S3: ellipse "OUTPUT" "WAIT" "IEOF"
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move down l from last ellipse.s
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S4: ellipse "OUTPUT" "CLOSED"
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move down l from 1st ellipse.s
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S2: ellipse "OUTPUT" "WAIT" "DRAIN"
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arrow "" "write_failed/" "shutdown_write" "send OCLOSE" from S1.e to S3.w
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arrow "obuf_empty ||" "write_failed/" "shutdown_write" "send OCLOSE" from S2.e to S4.w
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arrow from S1.s to S2.n
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box invis "rcvd IEOF/" "-" with .e at last arrow.c
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arrow from S3.s to S4.n
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box invis "rcvd IEOF/" "-" with .w at last arrow.c
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ellipse wid .9*ellipsewid ht .9*ellipseht at S4
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arrow "start" "" from S1.w+(-0.5,0) to S1.w
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The input buffer is filled with data from the socket
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(the socket represents the local consumer/producer of the
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The data is then sent over the INPUT-end (transmit-end) of the channel to the
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Data sent by the peer is received on the OUTPUT-end (receive-end),
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saved in the output buffer and written to the socket.
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If the local protocol instance has forwarded all data on the
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INPUT-end of the channel, it sends an IEOF message to the peer.
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If the peer receives the IEOF and has consumed all
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data he replies with an OCLOSE.
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When the local instance receives the OCLOSE
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he considers the INPUT-half of the channel closed.
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The peer has his OUTOUT-half closed.
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A channel can be deallocated by a protocol instance
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if both the INPUT- and the OUTOUT-half on his
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side of the channel are closed.
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Note that when an instance is unable to consume the
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received data, he is permitted to send an OCLOSE
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before the matching IEOF is received.
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nchan.ms
