Lua

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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Lua

local chilkat = require("chilkat")

-- 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.

local tunnel = chilkat.SshTunnel.new()

-- The fixed destination that accepted connections are forwarded to.
tunnel.dest_hostname = "db.internal.example.com"
tunnel.dest_port = 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).
tunnel.listen_bind_ip_address = "127.0.0.1"

local sshPort = 22
local success = tunnel:connect("ssh.example.com", sshPort)
if not success then
    print(tunnel.last_error_text)
    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.
local password = "mySshPassword"

success = tunnel:authenticate_pw("mySshLogin", password)
if not success then
    print(tunnel.last_error_text)
    return
end

-- Pass 0 to let the operating system choose an available port.  After BeginAccepting succeeds,
-- ListenPort contains the actual port that was bound.
success = tunnel:begin_accepting(0)
if not success then
    print(tunnel.last_error_text)
    return
end

print("Listening on 127.0.0.1 port " .. tunnel.listen_port)

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

local waitForThreadExit = true
success = tunnel:close_tunnel(waitForThreadExit)
if not success then
    print(tunnel.last_error_text)
    return
end