B4X

Send EOF on an SSH Channel

Demonstrates the Chilkat Ssh.ChannelSendEof method, which sends an SSH EOF message on a channel. The only argument is the channel number. EOF closes only the client-to-server direction; the application may still receive stdout, stderr, exit status, EOF, and CLOSE from the server.

Background: Many remote commands read standard input until it ends — wc, sort, cat and friends. Sending EOF is the SSH equivalent of pressing Ctrl+D: it tells the remote process no more input is coming so it can finish and emit results. After sending EOF, do not send more data on that channel; a later send may return true even though nothing is delivered.

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Dim success As Boolean = False

'  Demonstrates the Ssh.ChannelSendEof method, which sends an SSH EOF message on a channel.  The
'  only argument is the channel number.  EOF closes only the client-to-server direction; output
'  may still be received from the server.

Dim ssh As ChilkatSsh
ssh.Initialize("ssh")

Dim sshPort As Int = 22
success = ssh.Connect("ssh.example.com", sshPort)
If success = False Then
    Log(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 = "mySshPassword"

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


Dim channelNum As Int = ssh.OpenSessionChannel
If channelNum < 0 Then
    Log(ssh.LastErrorText)
    Return
End If


success = ssh.SendReqExec(channelNum, "wc -l")
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


'  Send input to the remote command.
success = ssh.ChannelSendString(channelNum, "line one" & Chr(10) & "line two" & Chr(10) & "line three" & Chr(10), "utf-8")
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


'  Signal that no more input will be sent.  Do not send more data on this channel afterward.
success = ssh.ChannelSendEof(channelNum)
If success = False Then
    Log(ssh.LastErrorText)
    Return
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

'  Output can still be received after EOF is sent.
success = ssh.ChannelReceiveToClose(channelNum)
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


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

Log(output)

ssh.Disconnect