VB.NET

Wait for a Message on Any SSH Channel

Demonstrates the Chilkat Ssh.WaitForChannelMessage method, which waits for the next SSH channel message on any channel. The only argument is the poll timeout: 0 for a nonblocking check, a positive value to wait that long, or a negative value to wait with no method-level timeout. It returns the channel number the message belongs to, -1 if nothing arrived before the timeout, or -2 on another error such as a lost connection.

Background: When several channels are active at once, waiting on one specific channel would block while others sit ready. This method is the multiplexed alternative — it returns as soon as any channel has activity and tells you which one, so a single loop can service them all. The explicit timeout argument governs the wait; shorter ReadTimeoutMs values do not cut it short.

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VB.NET

Dim success As Boolean = False

'  Demonstrates the Ssh.WaitForChannelMessage method, which waits for the next SSH channel
'  message on ANY channel.  The only argument is the poll timeout in milliseconds: 0 for a
'  nonblocking check, a positive value to wait that long, or a negative value to wait with no
'  method-level timeout.

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


'  Wait up to 5 seconds for the next channel message.  The return value is the channel number
'  the message belongs to, -1 if nothing arrived before the timeout, or -2 on another error.
Dim pollTimeoutMs As Integer = 5000
Dim result As Integer = ssh.WaitForChannelMessage(pollTimeoutMs)

If (result = -2) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


If (result = -1) Then
    Debug.WriteLine("No channel message arrived before the timeout.")
End If


If (result >= 0) Then
    Debug.WriteLine("Processed a message for channel " & result)
End If


ssh.Disconnect()