SSH Tunnel Static (Fixed-Destination) Port Forwarding

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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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#include <C_CkSshTunnel.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkSshTunnel tunnel;
    int sshPort;
    const char *password;
    BOOL waitForThreadExit;

    success = FALSE;

    //  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.

    tunnel = CkSshTunnel_Create();

    //  The fixed destination that accepted connections are forwarded to.
    CkSshTunnel_putDestHostname(tunnel,"db.internal.example.com");
    CkSshTunnel_putDestPort(tunnel,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).
    CkSshTunnel_putListenBindIpAddress(tunnel,"127.0.0.1");

    sshPort = 22;
    success = CkSshTunnel_Connect(tunnel,"ssh.example.com",sshPort);
    if (success == FALSE) {
        printf("%s\n",CkSshTunnel_lastErrorText(tunnel));
        CkSshTunnel_Dispose(tunnel);
        return;
    }

    //  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.
    password = "mySshPassword";

    success = CkSshTunnel_AuthenticatePw(tunnel,"mySshLogin",password);
    if (success == FALSE) {
        printf("%s\n",CkSshTunnel_lastErrorText(tunnel));
        CkSshTunnel_Dispose(tunnel);
        return;
    }

    //  Pass 0 to let the operating system choose an available port.  After BeginAccepting succeeds,
    //  ListenPort contains the actual port that was bound.
    success = CkSshTunnel_BeginAccepting(tunnel,0);
    if (success == FALSE) {
        printf("%s\n",CkSshTunnel_lastErrorText(tunnel));
        CkSshTunnel_Dispose(tunnel);
        return;
    }

    printf("Listening on 127.0.0.1 port %d\n",CkSshTunnel_getListenPort(tunnel));

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

    waitForThreadExit = TRUE;
    success = CkSshTunnel_CloseTunnel(tunnel,waitForThreadExit);
    if (success == FALSE) {
        printf("%s\n",CkSshTunnel_lastErrorText(tunnel));
        CkSshTunnel_Dispose(tunnel);
        return;
    }



    CkSshTunnel_Dispose(tunnel);

    }