Copyright (c) 1999 Markus Friedl. All rights reserved.
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OpenSSH Channel Close Protocol 1.5 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 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 arrow from S2.ne to S4.sw box invis "rcvd OCLOSE/ " with .e at last arrow.c box invis " send IEOF" with .w at last arrow.c
E
Channel Output State DiagramS 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
E
NotesThe 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 IEOF message to the peer. If the peer receives the IEOF and has consumed 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.
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 consume the received data, he is permitted to send an OCLOSE before the matching IEOF is received.