Delphi DLL

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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var
success: Boolean;
tunnel: HCkSshTunnel;
sshPort: Integer;
password: PWideChar;
waitForThreadExit: Boolean;

begin
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) then
  begin
    Memo1.Lines.Add(CkSshTunnel__lastErrorText(tunnel));
    Exit;
  end;

//  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) then
  begin
    Memo1.Lines.Add(CkSshTunnel__lastErrorText(tunnel));
    Exit;
  end;

//  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) then
  begin
    Memo1.Lines.Add(CkSshTunnel__lastErrorText(tunnel));
    Exit;
  end;
Memo1.Lines.Add('Listening on 127.0.0.1 port ' + IntToStr(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) then
  begin
    Memo1.Lines.Add(CkSshTunnel__lastErrorText(tunnel));
    Exit;
  end;

CkSshTunnel_Dispose(tunnel);