CSAW CTF 2013 - Misc 300 Life Solution in Golang -- WildcatSec

life.go

// life.go
// This file solves CSAW CTF 2013 - Misc 300
// Challenge was to take an ASCII Game-of-Life, advance by n generations, and return the new game, then repeat

package main

import (
	"fmt"
	"net"
	"regexp"
	"strconv"
	"strings"
)

func main() {
	// Connect to the server
	conn, err1 := net.Dial("tcp", "128.238.66.216:45678")
	if err1 != nil {
		fmt.Println(err1)
		return
	}

	var read []byte
	var err error
	var matched bool
	var connStatus error
	
	// while connected
	for connStatus == nil {

		// scan for Generations header
		matched = false
		for !matched {
			read = make([]byte, 4096)
			_, connStatus = conn.Read(read)
			matched, _ = regexp.Match(".*Generations.*", read)

			if matched == false {
				fmt.Print("Didn't match:\n", string(read))
				return // Ugly code is the result of hacky solutions
			}
		}

		re1 := regexp.MustCompile("[0-9]+ Gen") // Noncapturing groups don't work :(
		re2 := regexp.MustCompile("[0-9]+")
		generationsAsString := re2.FindString(re1.FindString(string(read)))
		fmt.Println(generationsAsString)
		generations, err := strconv.ParseInt(generationsAsString, 0, 32)
		if err != nil {
			fmt.Print(err)
			return
		}
		fmt.Println("Generations: ", generations)

		// Read the game board
		read = make([]byte, 4096)
		_, connStatus = conn.Read(read)

		gameRows := strings.Split(string(read), "\n")
		
		// Split the board into a 2D matrix
		game := make([][]rune, len(gameRows)-1)
		for i, row := range gameRows {
			if i == len(gameRows)-1 {
				break
			}
			game[i] = []rune(row)
			fmt.Println(row)
		}

		for i := int64(0); i < generations; i++ {
			game = step(game)
		}
		_, connStatus = conn.Write([]byte(toString(game)))
	}

	for err == nil {
		read = make([]byte, 4096)
		_, err = conn.Read(read)
		fmt.Println(string(read))
	}
}

func toString(game [][]rune) string {
	var res string
	for i := range game {
		res += string(game[i]) + "\n"
	}
	return res
}

func step(game [][]rune) [][]rune {
	newgame := make([][]rune, len(game))
	for i, row := range game {
		newgame[i] = make([]rune, len(row))
		for j, cell := range row {

			if cell == '#' {
				newgame[i][j] = '#'
			} else {
				neighbors := 0
				for x := i - 1; x <= i+1; x++ {
					for y := j - 1; y <= j+1; y++ {
						if x == i && y == j {
							continue
						}
						if game[x][y] == '*' {
							neighbors++
						}
					}
				}

				if cell == '*' && (neighbors == 2 || neighbors == 3) {
					newgame[i][j] = '*'
				} else if neighbors == 3 {
					newgame[i][j] = '*'
				} else {
					newgame[i][j] = ' '
				}
			}
		}
	}

	return newgame
}