.TL
OpenSSH Channel Close Protocol 1.5 Implementation
.SH
Channel Input State Diagram
.PS
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
S4: ellipse "INPUT" "CLOSED"
move down l from last ellipse.s
S3: ellipse "INPUT" "WAIT" "OCLOSED"
move down l from 1st ellipse.s
S2: ellipse "INPUT" "WAIT" "DRAIN"
arrow "" "rcvd OCLOSE/" "shutdown_read" "send IEOF" from S1.e to S4.w
arrow "ibuf_empty/" "send IEOF" from S2.e to S3.w
arrow from S1.s to S2.n
box invis "read_failed/" "shutdown_read" with .e at last arrow.c
arrow  from S3.n to S4.s
box invis "rcvd OCLOSE/" "-" with .w at last arrow.c
ellipse wid .9*ellipsewid ht .9*ellipseht at S4
arrow "start" "" from S1.w+(-0.5,0) to S1.w
.PE
.SH
Channel Output State Diagram
.PS
S1: ellipse "OUTPUT" "OPEN"
move right 2*l from last ellipse.e
S3: ellipse "OUTPUT" "WAIT" "IEOF"
move down l from last ellipse.s
S4: ellipse "OUTPUT" "CLOSED"
move down l from 1st ellipse.s
S2: ellipse "OUTPUT" "WAIT" "DRAIN"
arrow "" "write_failed/" "shutdown_write" "send OCLOSE" from S1.e to S3.w
arrow "obuf_empty ||" "write_failed/" "shutdown_write" "send OCLOSE" from S2.e to S4.w
arrow from S1.s to S2.n
box invis "rcvd IEOF/" "-" with .e at last arrow.c
arrow from S3.s to S4.n
box invis "rcvd IEOF/" "-" with .w at last arrow.c
ellipse wid .9*ellipsewid ht .9*ellipseht at S4
arrow "start" "" from S1.w+(-0.5,0) to S1.w
.PE
.SH
Notes
.PP
The input buffer is filled with data from the socket
(the socket represents the local comsumer/producer of the
forwarded channel).
The data is then sent over the INPUT-end of the channel to the
remote peer.
Data sent by the peer is received on the OUTPUT-end,
saved in the output buffer and written to the socket.
.PP
If the local protocol instance has forwarded all data on the
INPUT-end of the channel, it sends an IEOF message to the peer.
If the peer receives the IEOF and has comsumed all
data he replies with an OCLOSE.
When the local instance receives the OCLOSE
he considers the INPUT-half of the channel closed.
The peer has his OUTOUT-half closed.
.PP
A channel can be deallocated by a protocol instance
if both the INPUT- and the OUTOUT-half on his
side of the channel are closed.
Note that when an instance is unable to comsume the
received data, he is permitted to send an OCLOSE
before the matching IEOF is received.