Read an SSH Channel with a Byte Threshold

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Demonstrates the Chilkat Ssh.ChannelReadAndPoll2 method, which works like ChannelReadAndPoll but also returns once newly processed data brings the total buffered data to or above a byte threshold. The arguments are the channel number, the poll timeout, and the threshold.

The integer return value is -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or channel close was processed, or — when greater than 0 — the total bytes currently buffered for the channel (not the bytes newly received by this call).

load ./chilkat.dll

set success 0

#  Demonstrates the Ssh.ChannelReadAndPoll2 method, which works like ChannelReadAndPoll but also
#  returns once the total buffered data reaches or exceeds a byte threshold.  The 1st argument is
#  the channel number, the 2nd is the poll timeout, and the 3rd is the byte threshold.

set ssh [new_CkSsh]

set sshPort 22
set success [CkSsh_Connect $ssh "ssh.example.com" $sshPort]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

#  Normally you would not hard-code the password in source.  You should instead obtain it
#  from an interactive prompt, environment variable, or a secrets vault.
set password "mySshPassword"

set success [CkSsh_AuthenticatePw $ssh "mySshLogin" $password]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

set channelNum [CkSsh_OpenSessionChannel $ssh]
if {$channelNum < 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

#  Start a shell WITHOUT requesting a PTY.  Without a PTY the shell sees it is connected to a
#  raw data pipe and enters non-interactive mode: it suppresses the command prompt, does not
#  echo typed commands back, and skips interactive login scripts.  The output is therefore
#  clean and easily parseable -- but because no prompt is ever sent, code must not wait for
#  one.  Instead, have each command print a predictable marker, or wait for EOF / channel close.
set success [CkSsh_SendReqShell $ssh $channelNum]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

set success [CkSsh_ChannelSendString $ssh $channelNum "cat /var/log/syslog\n" "utf-8"]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

#  Return when output goes quiet for 500ms, or once about 64KB has been buffered.  The
#  threshold is not a hard buffer limit -- a whole SSH packet may push the total above it.
set pollTimeoutMs 500
set maxNumBytes 65536
#  The return value is: -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or
#  channel close was processed, or the total number of buffered bytes when greater than 0.
set result [CkSsh_ChannelReadAndPoll2 $ssh $channelNum $pollTimeoutMs $maxNumBytes]
if {$result == -1} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

if {$result == -2} then {
    puts "No channel data arrived before the timeout."
}

if {$result == 0} then {
    puts "EOF or channel close was processed.  Buffered data may still remain."
}

if {$result > 0} then {
    puts "Total bytes buffered: $result"
}

set output [CkSsh_getReceivedText $ssh $channelNum "utf-8"]
if {[CkSsh_get_LastMethodSuccess $ssh] == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

puts "$output"

CkSsh_Disconnect $ssh

delete_CkSsh $ssh