/*
 * Trap network connections by reading them a file indefinitely
 *
 * by wgs
 */
package main

import (
	"fmt"
	"flag"
	"io"
	"log"
	"net"
	"os"
	"bytes"
	"time"
)

// Default to HTTP response (works with ssh too!)
const BANNER = "HTTP/1.1 200 OK\n"
const FORMAT = "X: %s"

var count int
var banner string
var format string
var delay int
var msg []byte

func usage() {
	fmt.Fprint(os.Stderr, "usage: tarpit [-l listen] [-d delay] [-f FORMAT] [-b BANNER] file")
	os.Exit(2)
}

// Write a formatted string, one byte at a time
func delayPrint(c net.Conn, d time.Duration, p string, l string) error {
	b := fmt.Sprintf(p, l)
	for i := 0; i < len(b); i++ {
		time.Sleep(d)
		_, err := c.Write([]byte(b[i:i+1]))
		if err != nil {
			return err
		}
	}
	return nil
}

func tarpit(c net.Conn, delay int) {
	start := time.Now()
	addr := c.RemoteAddr().String()

	count++
	log.Printf("%s connected (%d total)\n", addr, count);

	b := bytes.NewBuffer(msg)
	d := time.Duration(delay) * time.Millisecond
	fmt := format

	delayPrint(c, d, "%s", banner)
	for {
		l, err := b.ReadBytes('\n')
		if err == io.EOF {
			b = bytes.NewBuffer(msg)
		} else if err != nil {
			delayPrint(c, d, fmt, "It's your lucky day…")
			break
		}
		err = delayPrint(c, d, fmt, string(l))
		if err != nil {
			break
		}
	}
	count--
	log.Printf("%s disconnected (trapped %s)", addr, time.Since(start));
}

func main() {
	var err error
	var laddr string

	flag.IntVar(&delay, "d", 1000, "Delay between bytes (ms)")
	flag.StringVar(&laddr, "l", ":1337", "Address to listen on")
	flag.StringVar(&banner, "b", BANNER, "Banner to send ahead of message")
	flag.StringVar(&format, "f", FORMAT, "Line format (%s is a file line)")
	flag.Parse()

	args := flag.Args()

	if len(args) != 1 {
		usage()
	}

	file := args[0]
	msg, err = os.ReadFile(file)
	if err != nil {
		log.Fatal(file, err)
	}

	l, err := net.Listen("tcp", laddr)
	if err != nil {
		log.Fatal(err)
	}

	// wait for connections
	for {
		c, err := l.Accept()
		if err != nil {
			log.Println(err)
			continue
		}
		// handle connections concurently
		go tarpit(c, delay)
	}
}