tunnel

tunnel is a very simple library that allows you to create multi-hop SSH tunnels. From the endpointof the tunnel you can then Dial() to create network connections, or you can Listen() for incoming connections.

This library supports both using the SSH Agent to load any keys you might need as well as loading keys from files or from []byte slices in PEM format.

Per default the implementation will keep track of any connections or listeners you make. If you shut this off you have to manage the connections yourself. I recommend using the default behavior (library tracks connections).

You can create multiple connections through the same tunnel.

Usage Examples

Please have a look in the examples directory for some usage examples.

Typical use

Import

Add the following import and run go mod tidy to add tunnel to your project.

import "github.com/borud/tunnel"

Creating the tunnel

This example just creates a tunnel with two hops

tun, err := tunnel.Create(
  tunnel.WithHop("user@first.example.com"), 
  tunnel.WithHop("user@second.example.com"), 
  tunnel.WithAgent(), 
  tunnel.WithHostKeyCallback(ssh.InsecureIgnoreHostKey()),
)

Dial

You can Dial to create a new connection over the tunnel like so:

  conn, err := tun.Dial("tcp", "service.example.com:4711")

If everything went according to plan you now have a tunnel that terminates at second.example.com (since it is the last hop) and connects from there to port 4711 on service.example.com

Listen

You can also listen on the remote endpoint.

listener, err := tunnel.Listen("tcp", ":80")

A note on Listen ports

When you want to Listen to remote ports that should be externally available, you have to make sure that the SSH daemon is configured to allow this. Please review the GatewayPorts and AllowTcpForwarding configuration options in sshd_config. If you were too lazy to read this paragraph and are just looking for a cut and paste, the config is:

GatewayPorts yes
AllowTcpForwarding yes