Bongcloud CTF challenge

bongcloud.go

package main

import (
	"errors"
	"fmt"
	"net"
	"time"
)

type ChessState struct {
	MoveNumber int
}

func (s *ChessState) NextMove() (move string, err error) {
	if s.MoveNumber == 0 {
		s.MoveNumber += 1
		return "e4", nil
	} else if s.MoveNumber == 1 {
		s.MoveNumber += 1
		return "Ke2", nil
	} else {
		return "", errors.New("No more moves needed")
	}
}

func SendString(conn net.Conn, s string) error {
	data := []byte(s)
	for i := range data {
		n, err := conn.Write(data[i : i+1])
		if n != 1 || err != nil {
			return errors.New("socket is donezo")
		}
		time.Sleep(50 * time.Millisecond)
	}
	return nil
}

func handleConnection(conn net.Conn) {
	defer conn.Close()
	state := ChessState{MoveNumber: 0}
	if SendString(conn, "Welcome to BSides Chess! Let's play! I'll play as white. Here goes!") != nil {
		return
	}
	time.Sleep(2 * time.Second)
	if SendString(conn, "\n\n") != nil {
		return
	}
	for {
		move, err := state.NextMove()
		if err != nil {
			SendString(conn, "\n\nSay it ain't so... It's too much! I resign!")
			return
		}
		if SendString(conn, fmt.Sprintf("%d: %s\n   ", state.MoveNumber, move)) != nil {
			return
		}
		recvData := make([]byte, 5)
		conn.Read(recvData)
	}
}

func main() {
	ln, err := net.Listen("tcp", ":8888")
	if err != nil {
		return
	}
	for {
		conn, err := ln.Accept()
		if err != nil {
			return
		}
		go handleConnection(conn)
	}
}