VB.NET

Get the Number of Bytes Buffered on an SSH Channel

Demonstrates the Chilkat Ssh.GetReceivedNumBytes method, which returns how many bytes are currently available in a channel's normal receive buffer. The only argument is the channel number. It returns -1 when the channel number is invalid or its retained resources have been released.

Background: This is a non-consuming look at how much is waiting, useful for deciding whether to retrieve now or keep reading, and for reporting progress on a large transfer. It counts only the normal receive buffer — bytes in the separate stderr buffer are excluded when StderrToStdout is false. Note that data received earlier can remain available even after a disconnect, so a positive count does not imply the connection is still up.

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Dim success As Boolean = False

'  Demonstrates the Ssh.GetReceivedNumBytes method, which returns the number of bytes currently
'  available in a channel's normal receive buffer.  The only argument is the channel number.
'  It returns -1 for an invalid channel or one whose resources have been released.

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


'  Find out how much is waiting before retrieving it.
Dim numBytes As Integer = ssh.GetReceivedNumBytes(channelNum)
If (numBytes < 0) Then
    Debug.WriteLine("Invalid channel, or its resources were already released.")
    Exit Sub
End If


Debug.WriteLine("Bytes available: " & numBytes)

Dim output As String = ssh.GetReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If

Debug.WriteLine(output)

ssh.Disconnect()