VB.NET

Peek at Buffered SSH Channel Text

Demonstrates the Chilkat Ssh.PeekReceivedText method, which returns the text currently buffered for a channel, decoded with the given charset, without removing any bytes. The first argument is the channel number and the second is the charset.

Background: Every other retrieval method consumes the buffer, which is awkward when you only want to know whether the output you are waiting for has arrived yet. Because peeking is nondestructive, you can inspect, decide, and still retrieve the data normally afterward — the basis of a poll-and-check loop. Note that StripColorCodes is not applied here, so terminal escape sequences appear exactly as buffered.

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Dim success As Boolean = False

'  Demonstrates the Ssh.PeekReceivedText method, which returns the text currently buffered for a
'  channel without removing any bytes.  The 1st argument is the channel number and the 2nd is
'  the charset.

Dim ssh As New Chilkat.Ssh

Dim sshPort As Integer = 22
success = ssh.Connect("ssh.example.com",sshPort)
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
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 = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


Dim channelNum As Integer = ssh.OpenSessionChannel()
If (channelNum < 0) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


success = ssh.SendReqExec(channelNum,"ls -l /tmp")
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  IMPORTANT: Set a read timeout.  ReadTimeoutMs defaults to 0, which means no limit -- without
'  it, this call waits forever if the server never sends channel close.
ssh.ReadTimeoutMs = 15000

success = ssh.ChannelReceiveToClose(channelNum)
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  Look at the buffered text without consuming it.  This is useful for checking whether the
'  expected output has arrived yet.
Dim peeked As String = ssh.PeekReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If

Debug.WriteLine("Peeked: " & peeked)

'  The bytes are still buffered, so retrieving them still returns the same text.
Dim output As String = ssh.GetReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If

Debug.WriteLine("Retrieved: " & output)

ssh.Disconnect()