B4X

Multiple SendReqExec on the Same Connection

Demonstrates running a series of commands on one SSH connection using SendReqExec. Each exec request requires its own logical channel — this is not a separate SSH connection, just a new session channel on the existing one.

Background: An SSH session channel is single-use for an exec request: once the command runs and the server closes the channel, that channel cannot be reused. Opening a fresh channel per command is cheap, since the expensive work — the TCP connection, key exchange, and authentication — is done once and shared. This is why running ten commands over one connection is far faster than connecting ten times.

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Dim success As Boolean = False

'  This example requires the Chilkat API to have been previously unlocked.
'  See Global Unlock Sample for sample code.

'  Demonstrates running a series of commands on one SSH connection using SendReqExec.  Each exec
'  request requires its own logical channel.  This is not a new SSH connection -- it is simply a
'  new session channel on the existing one.

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

Dim hostname As String = "ssh.example.com"
Dim port As Int = 22
success = ssh.Connect(hostname, port)
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


'  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

'  ---- 1st command, on its own session channel ----
Dim channelNum As Int = ssh.OpenSessionChannel
If channelNum < 0 Then
    Log(ssh.LastErrorText)
    Return
End If


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


success = ssh.ChannelReceiveToClose(channelNum)
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


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

Log(cmdOutput)
Log("----")

'  ---- 2nd command, on a NEW session channel over the same connection ----
channelNum = ssh.OpenSessionChannel
If channelNum < 0 Then
    Log(ssh.LastErrorText)
    Return
End If


success = ssh.SendReqExec(channelNum, "nslookup chilkatsoft.com")
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


success = ssh.ChannelReceiveToClose(channelNum)
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


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

Log(cmdOutput)

ssh.Disconnect