Visual FoxPro

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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LOCAL lnSuccess
LOCAL loTunnel
LOCAL lnSshPort
LOCAL lcPassword
LOCAL lnWaitForThreadExit

lnSuccess = 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.

loTunnel = CreateObject('Chilkat.SshTunnel')

*  The fixed destination that accepted connections are forwarded to.
loTunnel.DestHostname = "db.internal.example.com"
loTunnel.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).
loTunnel.ListenBindIpAddress = "127.0.0.1"

lnSshPort = 22
lnSuccess = loTunnel.Connect("ssh.example.com",lnSshPort)
IF (lnSuccess = 0) THEN
    ? loTunnel.LastErrorText
    RELEASE loTunnel
    CANCEL
ENDIF

*  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.
lcPassword = "mySshPassword"

lnSuccess = loTunnel.AuthenticatePw("mySshLogin",lcPassword)
IF (lnSuccess = 0) THEN
    ? loTunnel.LastErrorText
    RELEASE loTunnel
    CANCEL
ENDIF

*  Pass 0 to let the operating system choose an available port.  After BeginAccepting succeeds,
*  ListenPort contains the actual port that was bound.
lnSuccess = loTunnel.BeginAccepting(0)
IF (lnSuccess = 0) THEN
    ? loTunnel.LastErrorText
    RELEASE loTunnel
    CANCEL
ENDIF

? "Listening on 127.0.0.1 port " + STR(loTunnel.ListenPort)

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

lnWaitForThreadExit = 1
lnSuccess = loTunnel.CloseTunnel(lnWaitForThreadExit)
IF (lnSuccess = 0) THEN
    ? loTunnel.LastErrorText
    RELEASE loTunnel
    CANCEL
ENDIF

RELEASE loTunnel