PowerBuilder

SSH Tunnel Static (Fixed-Destination) Port Forwarding

Demonstrates fixed-destination port forwarding with the DestHostname, DestPort, ListenBindIpAddress, and ListenPort properties. Every local connection accepted by the listener is forwarded to the same fixed destination through the SSH server.

Background: This is the classic ssh -L scenario: expose a single remote service — a database, an internal web app — at a local port. Binding the listener to 127.0.0.1 keeps the tunnel private to the local machine, whereas 0.0.0.0 would let other hosts route through it. Passing 0 to BeginAccepting lets the OS pick a free port, which ListenPort then reports — handy when a fixed port might already be in use.

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integer li_rc
integer li_Success
oleobject loo_Tunnel
integer li_SshPort
string ls_Password
integer li_WaitForThreadExit

li_Success = 0

//  Demonstrates fixed-destination (static) port forwarding with the SshTunnel properties
//  DestHostname, DestPort, ListenBindIpAddress, and ListenPort.
//  
//  Every local connection accepted by the listener is forwarded to the same fixed destination
//  through the SSH server.

loo_Tunnel = create oleobject
li_rc = loo_Tunnel.ConnectToNewObject("Chilkat.SshTunnel")
if li_rc < 0 then
    destroy loo_Tunnel
    MessageBox("Error","Connecting to COM object failed")
    return
end if

//  The fixed destination that accepted connections are forwarded to.
loo_Tunnel.DestHostname = "db.internal.example.com"
loo_Tunnel.DestPort = 5432

//  Bind the listener to loopback so only local processes can use the tunnel.  Use "0.0.0.0" to
//  accept connections from other machines (less secure).
loo_Tunnel.ListenBindIpAddress = "127.0.0.1"

li_SshPort = 22
li_Success = loo_Tunnel.Connect("ssh.example.com",li_SshPort)
if li_Success = 0 then
    Write-Debug loo_Tunnel.LastErrorText
    destroy loo_Tunnel
    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.
ls_Password = "mySshPassword"

li_Success = loo_Tunnel.AuthenticatePw("mySshLogin",ls_Password)
if li_Success = 0 then
    Write-Debug loo_Tunnel.LastErrorText
    destroy loo_Tunnel
    return
end if

//  Pass 0 to let the operating system choose an available port.  After BeginAccepting succeeds,
//  ListenPort contains the actual port that was bound.
li_Success = loo_Tunnel.BeginAccepting(0)
if li_Success = 0 then
    Write-Debug loo_Tunnel.LastErrorText
    destroy loo_Tunnel
    return
end if

Write-Debug "Listening on 127.0.0.1 port " + string(loo_Tunnel.ListenPort)

//  Applications now connect to 127.0.0.1:ListenPort as if it were the database server.

li_WaitForThreadExit = 1
li_Success = loo_Tunnel.CloseTunnel(li_WaitForThreadExit)
if li_Success = 0 then
    Write-Debug loo_Tunnel.LastErrorText
    destroy loo_Tunnel
    return
end if



destroy loo_Tunnel