SQL Server

SSH Tunnel Dynamic Port Forwarding (Local SOCKS Proxy)

Demonstrates dynamic port forwarding with the DynamicPortForwarding, InboundSocksUsername, and InboundSocksPassword properties. In dynamic mode the listener acts as a local SOCKS proxy, so each client chooses its own destination and one tunnel can reach many hosts on the SSH server's network.

Background: This is the ssh -D scenario: instead of pinning one local port to one destination, the tunnel speaks SOCKS and lets each client name where it wants to go. Any SOCKS-capable application — a browser, a mail client — can then reach the remote network through the single tunnel. Setting an inbound SOCKS username and password restricts who may use the local proxy, which matters because it would otherwise accept unauthenticated connections from any local process.

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-- Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @success int
    SELECT @success = 0

    --  Demonstrates dynamic port forwarding with the SshTunnel properties DynamicPortForwarding,
    --  InboundSocksUsername, and InboundSocksPassword.
    --  
    --  In dynamic mode the listener behaves as a local SOCKS proxy: each client chooses its own
    --  destination, so one tunnel can reach many hosts on the SSH server's network.

    DECLARE @tunnel int
    EXEC @hr = sp_OACreate 'Chilkat.SshTunnel', @tunnel OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    --  Enable dynamic (SOCKS) forwarding instead of a single fixed destination.  No DestHostname or
    --  DestPort is needed.
    EXEC sp_OASetProperty @tunnel, 'DynamicPortForwarding', 1

    --  Optionally require inbound SOCKS5 clients to authenticate with the local proxy.  If left unset,
    --  the local proxy accepts unauthenticated SOCKS4 and SOCKS5 connections.
    EXEC sp_OASetProperty @tunnel, 'InboundSocksUsername', 'myLocalSocksLogin'
    EXEC sp_OASetProperty @tunnel, 'InboundSocksPassword', 'myLocalSocksPassword'

    DECLARE @sshPort int
    SELECT @sshPort = 22
    EXEC sp_OAMethod @tunnel, 'Connect', @success OUT, 'ssh.example.com', @sshPort
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @tunnel, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @tunnel
        RETURN
      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.
    DECLARE @password nvarchar(4000)
    SELECT @password = 'mySshPassword'

    EXEC sp_OAMethod @tunnel, 'AuthenticatePw', @success OUT, 'mySshLogin', @password
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @tunnel, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @tunnel
        RETURN
      END

    --  Start the local SOCKS proxy on port 1080.  SOCKS-capable clients point at 127.0.0.1:1080.
    DECLARE @listenPort int
    SELECT @listenPort = 1080
    EXEC sp_OAMethod @tunnel, 'BeginAccepting', @success OUT, @listenPort
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @tunnel, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @tunnel
        RETURN
      END

    PRINT 'Local SOCKS proxy running on port ' + @listenPort

    DECLARE @waitForThreadExit int
    SELECT @waitForThreadExit = 1
    EXEC sp_OAMethod @tunnel, 'CloseTunnel', @success OUT, @waitForThreadExit
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @tunnel, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @tunnel
        RETURN
      END

    EXEC @hr = sp_OADestroy @tunnel


END
GO