tunnel

go-tunnel

Listen for connections made to a remote machine.

Your typical net.Listen() call lets you listen for new connections on a local port. go-tunnel provides an abstraction that lets your application listen for new connections on a port on a remote machine. It also has special support for HTTP listening which allows a client to ask to listen for connections just to a specific HTTP hostname (or on a random one).

The demo

We're going to serve a simple HTTP service on a public URL by just adding a single library call.

Here's a simple Go HTTP server that listens on port 9090 of your local machine.

package main

import (
	"net/http"
	"io"
	"fmt"
)

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Printf("Serving hello world page!\n")
		io.WriteString(w, "Hello world!\n")
	})

	err = http.ServeAndListen(":9090")
	if err != nil {
		panic(err)
	}
}

Here's the same simple Go HTTP server that listens on a randomly-assigned public hostname assigned by the free service I provide on airlock.io:

package main

import (
	"net/http"
	"io"
	"fmt"
	"github.com/inconshreveable/go-tunnel"
)

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Printf("Serving hello world page!\n")
		io.WriteString(w, "Hello world!\n")
	})

	tun, err := tunnel.ListenHTTP()
	if err != nil {
		panic(err)
	}

	fmt.Printf("Serving at: %v\n", tun.Addr())

	err = http.Serve(tun, nil)
	if err != nil {
		panic(err)
	}
}

Instead of calling http.ListenAndServe, you call http.Serve and pass in the tunnel listener you create by a call to tunnel.ListenHTTP()

The Tunnel object

The coolest part of the library is that calls to Session.Listen(), Session.Listen*(), as well as the top level calls ListenHTTP() and ListenTCP() return a Tunnel object.

Tunnel objects implement net.Listener. This means you can pass them into http.Serve like in the example above. You can accept new connections from them. If you print the Tunnel.Addr(), you'll get the public address you can connect to the tunnel with.

The connections returned by the Tunnel.Accept() method even behave like they were accepted on the remote machine. If you print .RemoteAddr() on a connection accepted from a tunnel, you will get back the address of the remote address of the public connection.

.Close() a tunnel to return the port or virtual hostname to the server so it may be allocated to another client, just like you would with a TCP net.Listener.

Tunneling over a custom server

If you want to connect to a custom server instead of using the free public server, you'll need to first create a session to a different tunneling service.

sess, err := tunnel.Dial("example.com:1234")
if err != nil {
	panic(err)
}

// now bind for remote connections
tun, err := sess.ListenTCP(tcpOptions)

Customizing listen calls

The Listen calls on a Session are a little more flexible than the top-level calls. They let you listen with a set of options that can customize the tunnel you bind.

Binding a specific port

For TCP tunnels, you may request the server bind a specific port for you instead of a random one:

import (
	"github.com/inconshreveable/go-tunnel"
	"github.com/inconshreveable/go-tunnel/proto"
)

func main() {
	sess, err := tunnel.Dial("example.com:1234")
	if err != nil {
		panic(err)
	}

	// now bind for remote connections
	tun, err := sess.ListenTCP(&proto.TCPOptions{RemotePort: 12345})
}

Binding with a specific subdomain and authentication

import (
	"github.com/inconshreveable/go-tunnel"
	"github.com/inconshreveable/go-tunnel/proto"
)

func main() {
	sess, err := tunnel.Dial("example.com:1234")
	if err != nil {
		panic(err)
	}

	// now bind for remote connections
	tun, err := sess.ListenHTTP(&proto.HTTPPOptions{Auth: "user:secret", Subdomain: "example"})
}

Custom tunnel servers with the server library

The go-tunnel library also has code that lets you create custom tunneling servers. Typical server setup involves creating a set of binders, and then running the server. This setup would set up a tunnel server that listenson port 12345 for new TLS-encrypted tunnel sessions and allows binding http tunnels only:

import (
	"github.com/inconshreveable/go-tunnel/server"
	"github.com/inconshreveable/go-tunnel/server/binder"
)

func main() {
	binders := make(map[string] binders.Binder)

	if binders["http"], err = binder.NewHTTPBinder(":80", "example.com", 10 * time.Second); err != nil {
		panic(err)
	}

	server, err := server.ServeTLS("tcp", ":12345", exampleDotComTlsConfig, binders)
	if err != nil {
		panic(err)
	}

	server.Run()
}

You can inject custom behavior into the tunneling server by creating a custom set of server.SessionHooks and server.TunnelHooks and setting those properties on your Server object.

API Documentation

API documentation is available on godoc: https://godoc.org/github.com/inconshreveable/go-tunnel