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).

Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

$success = $false

#  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.

$ssh = New-Object Chilkat.Ssh

$sshPort = 22
$success = $ssh.Connect("ssh.example.com",$sshPort)
if ($success -eq $false) {
    $($ssh.LastErrorText)
    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.
$password = "mySshPassword"

$success = $ssh.AuthenticatePw("mySshLogin",$password)
if ($success -eq $false) {
    $($ssh.LastErrorText)
    exit
}

$channelNum = $ssh.OpenSessionChannel()
if ($channelNum -lt 0) {
    $($ssh.LastErrorText)
    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.
$success = $ssh.SendReqShell($channelNum)
if ($success -eq $false) {
    $($ssh.LastErrorText)
    exit
}

$success = $ssh.ChannelSendString($channelNum,"cat /var/log/syslog`n","utf-8")
if ($success -eq $false) {
    $($ssh.LastErrorText)
    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.
$pollTimeoutMs = 500
$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.
$result = $ssh.ChannelReadAndPoll2($channelNum,$pollTimeoutMs,$maxNumBytes)
if ($result -eq -1) {
    $($ssh.LastErrorText)
    exit
}

if ($result -eq -2) {
    $("No channel data arrived before the timeout.")
}

if ($result -eq 0) {
    $("EOF or channel close was processed.  Buffered data may still remain.")
}

if ($result -gt 0) {
    $("Total bytes buffered: " + $result)
}

$output = $ssh.GetReceivedText($channelNum,"utf-8")
if ($ssh.LastMethodSuccess -eq $false) {
    $($ssh.LastErrorText)
    exit
}

$($output)

$ssh.Disconnect()