B4X

Open a direct-tcpip Channel (SSH Port Forwarding)

Demonstrates the Chilkat Ssh.OpenDirectTcpIpChannel method, which opens a direct-tcpip channel through the SSH server to a target host and port. The first argument is the target hostname and the second is the target port. It returns the channel number, or -1 on failure.

Background: This is SSH local port forwarding at the API level: the channel carries ordinary TCP traffic to a service that may be reachable only from the SSH server's network — a database, an internal web app, a message broker. The key detail is that the server resolves the target name, not your machine, so it must resolve and be reachable there. Supplying a numeric IPv4 address avoids remote DNS resolution entirely.

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Dim success As Boolean = False

'  Demonstrates the Ssh.OpenDirectTcpIpChannel method, which opens a direct-tcpip channel
'  through the SSH server to a target host and port.  The 1st argument is the target hostname
'  and the 2nd is the target port.  It returns the channel number, or -1 on failure.

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


'  The target name is resolved by the SSH server, not by this computer, so it must be
'  reachable from the server's network.
Dim targetHostname As String = "db.internal.example.com"
Dim targetPort As Int = 5432
Dim channelNum As Int = ssh.OpenDirectTcpIpChannel(targetHostname, targetPort)
If channelNum < 0 Then
    Log(ssh.LastErrorText)
    Return
End If


Log("Opened direct-tcpip channel: " & channelNum)

'  The channel now carries ordinary TCP data to the target, tunneled over SSH.

ssh.Disconnect