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Poll an SSH Channel for Incoming Data

Demonstrates the Chilkat Ssh.ChannelPoll method, which polls a channel for incoming messages, waiting at most the given number of milliseconds. The first argument is the channel number and the second is the poll timeout; pass 0 for a nonblocking poll.

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).

Background: ChannelPoll gives you an explicit, per-call wait, which is what an event loop or responsive UI needs — poll briefly, do other work, poll again. Importantly, the timeout you pass governs the wait: shorter ReadTimeoutMs or IdleTimeoutMs values do not cut it short. A -2 return simply means nothing new arrived, which is normal when polling.

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Local $bSuccess = False

;  Demonstrates the Ssh.ChannelPoll method, which polls a channel for incoming messages, waiting
;  at most the given number of milliseconds.  The 1st argument is the channel number and the 2nd
;  is the poll timeout.  Pass 0 for a nonblocking poll.

$oSsh = ObjCreate("Chilkat.Ssh")

Local $iSshPort = 22
$bSuccess = $oSsh.Connect("ssh.example.com",$iSshPort)
If ($bSuccess = False) Then
    ConsoleWrite($oSsh.LastErrorText & @CRLF)
    Exit
EndIf

;  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.
Local $sPassword = "mySshPassword"

$bSuccess = $oSsh.AuthenticatePw("mySshLogin",$sPassword)
If ($bSuccess = False) Then
    ConsoleWrite($oSsh.LastErrorText & @CRLF)
    Exit
EndIf

Local $iChannelNum = $oSsh.OpenSessionChannel()
If ($iChannelNum < 0) Then
    ConsoleWrite($oSsh.LastErrorText & @CRLF)
    Exit
EndIf

;  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.
$bSuccess = $oSsh.SendReqShell($iChannelNum)
If ($bSuccess = False) Then
    ConsoleWrite($oSsh.LastErrorText & @CRLF)
    Exit
EndIf

$bSuccess = $oSsh.ChannelSendString($iChannelNum,"date" & @LF,"utf-8")
If ($bSuccess = False) Then
    ConsoleWrite($oSsh.LastErrorText & @CRLF)
    Exit
EndIf

;  Wait up to 3 seconds for channel data.
Local $iPollTimeoutMs = 3000
;  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.
Local $iResult = $oSsh.ChannelPoll($iChannelNum,$iPollTimeoutMs)
If ($iResult = -1) Then
    ConsoleWrite($oSsh.LastErrorText & @CRLF)
    Exit
EndIf

If ($iResult = -2) Then
    ConsoleWrite("No channel data arrived before the timeout." & @CRLF)
EndIf

If ($iResult = 0) Then
    ConsoleWrite("EOF or channel close was processed.  Buffered data may still remain." & @CRLF)
EndIf

If ($iResult > 0) Then
    ConsoleWrite("Total bytes buffered: " & $iResult & @CRLF)
EndIf

Local $sOutput = $oSsh.GetReceivedText($iChannelNum,"utf-8")
If ($oSsh.LastMethodSuccess = False) Then
    ConsoleWrite($oSsh.LastErrorText & @CRLF)
    Exit
EndIf

ConsoleWrite($sOutput & @CRLF)

$oSsh.Disconnect