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).

Dim success As Boolean
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.

Dim ssh As New Chilkat.Ssh

Dim sshPort As Int32
sshPort = 22
success = ssh.Connect("ssh.example.com",sshPort)
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

//  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.
Dim password As String
password = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

Dim channelNum As Int32
channelNum = ssh.OpenSessionChannel()
If (channelNum < 0) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

//  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 = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

success = ssh.ChannelSendString(channelNum,"cat /var/log/syslog" + EndOfLine.Unix,"utf-8")
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

//  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.
Dim pollTimeoutMs As Int32
pollTimeoutMs = 500
Dim maxNumBytes As Int32
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.
Dim result As Int32
result = ssh.ChannelReadAndPoll2(channelNum,pollTimeoutMs,maxNumBytes)
If (result = -1) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

If (result = -2) Then
    System.DebugLog("No channel data arrived before the timeout.")
End If

If (result = 0) Then
    System.DebugLog("EOF or channel close was processed.  Buffered data may still remain.")
End If

If (result > 0) Then
    System.DebugLog("Total bytes buffered: " + Str(result))
End If

Dim output As String
output = ssh.GetReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

System.DebugLog(output)

ssh.Disconnect