github.com/jgivc/go-telnet

go-telnet

Package telnet provides TELNET and TELNETS client and server implementations, for the Go programming language.

The telnet package provides an API in a style similar to the "net/http" library that is part of the Go standard library, including support for "middleware".

(TELNETS is secure TELNET, with the TELNET protocol over a secured TLS (or SSL) connection.)

Documention

Online documentation, which includes examples, can be found at: http://godoc.org/github.com/reiver/go-telnet

Very Simple TELNET Server Example

A very very simple TELNET server is shown in the following code.

This particular TELNET server just echos back to the user anything they "submit" to the server.

(By default, a TELNET client does not send anything to the server until the [Enter] key is pressed. "Submit" means typing something and then pressing the [Enter] key.)

package main

import (
	"github.com/reiver/go-telnet"
)

func main() {

	var handler telnet.Handler = telnet.EchoHandler
	
	err := telnet.ListenAndServe(":5555", handler)
	if nil != err {
		//@TODO: Handle this error better.
		panic(err)
	}
}

If you wanted to test out this very very simple TELNET server, if you were on the same computer it was running, you could connect to it using the bash command:

telnet localhost 5555

(Note that we use the same TCP port number -- "5555" -- as we had in our code. That is important, as the value used by your TELNET server and the value used by your TELNET client must match.)

Very Simple (Secure) TELNETS Server Example

TELNETS is the secure version of TELNET.

The code to make a TELNETS server is very similar to the code to make a TELNET server. (The difference between we use the telnet.ListenAndServeTLS func instead of the telnet.ListenAndServe func.)

package main

import (
	"github.com/reiver/go-telnet"
)

func main() {

	var handler telnet.Handler = telnet.EchoHandler
	
	err := telnet.ListenAndServeTLS(":5555", "cert.pem", "key.pem", handler)
	if nil != err {
		//@TODO: Handle this error better.
		panic(err)
	}
}

If you wanted to test out this very very simple TELNETS server, get the telnets client program from here: https://github.com/reiver/telnets

TELNET Client Example:

package main

import (
	"github.com/reiver/go-telnet"
)

func main() {
	var caller telnet.Caller = telnet.StandardCaller

	//@TOOD: replace "example.net:5555" with address you want to connect to.
	telnet.DialToAndCall("example.net:5555", caller)
}

TELNETS Client Example:

package main

import (
	"github.com/reiver/go-telnet"

	"crypto/tls"
)

func main() {
	//@TODO: Configure the TLS connection here, if you need to.
	tlsConfig := &tls.Config{}

	var caller telnet.Caller = telnet.StandardCaller

	//@TOOD: replace "example.net:5555" with address you want to connect to.
	telnet.DialToAndCallTLS("example.net:5555", caller, tlsConfig)
}

TELNET Shell Server Example

A more useful TELNET servers can be made using the "github.com/reiver/go-telnet/telsh" sub-package.

For example:

package main


import (
	"github.com/reiver/go-oi"
	"github.com/reiver/go-telnet"
	"github.com/reiver/go-telnet/telsh"

	"io"
	"time"
)



func fiveHandler(stdin io.ReadCloser, stdout io.WriteCloser, stderr io.WriteCloser, args ...string) error {
	oi.LongWriteString(stdout, "The number FIVE looks like this: 5\r\n")

	return nil
}

func fiveProducer(ctx telnet.Context, name string, args ...string) telsh.Handler{
	return telsh.PromoteHandlerFunc(fiveHandler)
}



func danceHandler(stdin io.ReadCloser, stdout io.WriteCloser, stderr io.WriteCloser, args ...string) error {
	for i:=0; i<20; i++ {
		oi.LongWriteString(stdout, "\r⠋")
		time.Sleep(50*time.Millisecond)

		oi.LongWriteString(stdout, "\r⠙")
		time.Sleep(50*time.Millisecond)

		oi.LongWriteString(stdout, "\r⠹")
		time.Sleep(50*time.Millisecond)

		oi.LongWriteString(stdout, "\r⠸")
		time.Sleep(50*time.Millisecond)

		oi.LongWriteString(stdout, "\r⠼")
		time.Sleep(50*time.Millisecond)

		oi.LongWriteString(stdout, "\r⠴")
		time.Sleep(50*time.Millisecond)

		oi.LongWriteString(stdout, "\r⠦")
		time.Sleep(50*time.Millisecond)

		oi.LongWriteString(stdout, "\r⠧")
		time.Sleep(50*time.Millisecond)

		oi.LongWriteString(stdout, "\r⠇")
		time.Sleep(50*time.Millisecond)

		oi.LongWriteString(stdout, "\r⠏")
		time.Sleep(50*time.Millisecond)
	}
	oi.LongWriteString(stdout, "\r \r\n")

	return nil
}

func danceProducer(ctx telnet.Context, name string, args ...string) telsh.Handler{

	return telsh.PromoteHandlerFunc(danceHandler)
}


func main() {

	shellHandler := telsh.NewShellHandler()

	shellHandler.WelcomeMessage = `
 __          __ ______  _        _____   ____   __  __  ______ 
 \ \        / /|  ____|| |      / ____| / __ \ |  \/  ||  ____|
  \ \  /\  / / | |__   | |     | |     | |  | || \  / || |__   
   \ \/  \/ /  |  __|  | |     | |     | |  | || |\/| ||  __|  
    \  /\  /   | |____ | |____ | |____ | |__| || |  | || |____ 
     \/  \/    |______||______| \_____| \____/ |_|  |_||______|

`


	// Register the "five" command.
	commandName     := "five"
	commandProducer := telsh.ProducerFunc(fiveProducer)

	shellHandler.Register(commandName, commandProducer)



	// Register the "dance" command.
	commandName      = "dance"
	commandProducer  = telsh.ProducerFunc(danceProducer)

	shellHandler.Register(commandName, commandProducer)



	shellHandler.Register("dance", telsh.ProducerFunc(danceProducer))

	addr := ":5555"
	if err := telnet.ListenAndServe(addr, shellHandler); nil != err {
		panic(err)
	}
}

TELNET servers made using the "github.com/reiver/go-telnet/telsh" sub-package will often be more useful as it makes it easier for you to create a shell interface.

More Information

There is a lot more information about documentation on all this here: http://godoc.org/github.com/reiver/go-telnet

(You should really read those.)