package main

// Embarrassingly quick and dirty Go program to reboot a TP-Link TD-8840 ADSL modem.
// Will possibly work on other devices with slight modifications.

import (
    "github.com/ziutek/telnet"
    "log"
    "os"
    "time"
    // "fmt"
)

const timeout = 5 * time.Second

func checkErr(err error) {
    if err != nil {
        log.Fatalln("Error:", err)
    }
}

func expect(t *telnet.Conn, d ...string) {
    checkErr(t.SetReadDeadline(time.Now().Add(timeout)))
    checkErr(t.SkipUntil(d...))
}

func sendln(t *telnet.Conn, s string) {
    checkErr(t.SetWriteDeadline(time.Now().Add(timeout)))
    buf := make([]byte, len(s)+1)
    copy(buf, s)
    buf[len(s)] = '\n'
    _, err := t.Write(buf)
    checkErr(err)
}

func briefDelay() {
    time.Sleep(100 * time.Millisecond)
}

func longDelay() {
    time.Sleep(2000 * time.Millisecond)
}

func main() {
    if len(os.Args) != 2 {
        log.Printf("Usage: %s HOST", os.Args[0])
        return
    }
    dst := os.Args[1]

    t, err := telnet.Dial("tcp", dst + ":23")
    checkErr(err)
    // fmt.Println("connected..")

    t.SetUnixWriteMode(true)

    expect(t, "username:")
    briefDelay()
    sendln(t, "admin")
    // fmt.Println("sent username..")

    expect(t, "password:")
    briefDelay()
    sendln(t, "admin")
    // fmt.Println("sent password..")

    longDelay()
    sendln(t, "dev reboot")

    longDelay()
}