Telnet

Go package for creating a Telnet protocol ReadWriter, which would typically be used to create a TCP telnet server.

Correctness is the primary focus and performance is secondary.

Options included:

• Echo us
• Suppress Go Ahead (SGA)
• Terminal-Type

Refer to the Option interface in USAGE for information about implementing other options.

Specifications:

Document	Description
RFC854	Telnet Protocol Specification
RFC855	Telnet Option Specifications
RFC857	Telnet Echo Option
RFC858	Telnet Suppress Go Ahead Option
RFC1091	Telnet Terminal-Type Option
RFC1143	The Q Method of Implementing TELNET Option Negotiation

Installation

$ go get github.com/ebarkie/telnet{,/option}

Usage

See USAGE.

Example

package main

import (
	"io"
	"log/slog"
	"net"

	"github.com/ebarkie/telnet"
)

func serve(conn net.Conn) {
	defer conn.Close()
	defer slog.Info("connection closed", "addr", conn.RemoteAddr())

	// Create telnet ReadWriter with no options.
	tn := telnet.NewReadWriter(conn)

	// Welcome banner.
	tn.Write([]byte("Welcome to a test telnet server!\r\n\r\n"))

	// Process input until connection is closed.
	buf := make([]byte, 1024)
	for {
		tn.Write([]byte("> "))
		n, err := tn.Read(buf)
		if err == io.EOF {
			return
		}
		slog.Info("read", "data", buf[:n], "n", n)
	}
}

func main() {
	// Create TCP listener.
	addr := net.JoinHostPort("127.0.0.1", "8023")
	slog.Info("listening", "addr", addr)
	l, err := net.Listen("tcp", addr)
	if err != nil {
		panic(err)
	}

	for {
		conn, err := l.Accept()
		if err != nil {
			slog.Error("accept error", "err", err)
			continue
		}
		slog.Info("accepted connection", "addr", conn.RemoteAddr())
		go serve(conn)
	}
}

License

Copyright (c) 2018-2020 Eric Barkie. All rights reserved.
Use of this source code is governed by the MIT license that can be found in the LICENSE file.