protohackers/cmd/mobinthemiddle/main.go

package main

import (
	"bytes"
	"fmt"
	"io"
	"net"
	"strings"
)

const tonyAddr = "7YWHMfk9JZe0LM0g1ZauHuiSxhI"

func hack(data []byte) []byte {
	sp := strings.Split(string(data), " ")
	for i, _ := range sp {
		if len(sp[i]) == 0 || sp[i][0] != '7' || len(sp[i]) < 26 || len(sp[i]) > 35 {
			continue
		}
		s := sp[i]
		if sp[i][len(sp[i])-1] == '\n' {
			sp[i] = tonyAddr + "\n"
		} else {
			sp[i] = tonyAddr
		}
		fmt.Printf("Rewrote %s to %s\n", s, tonyAddr)
	}
	return []byte(strings.Join(sp, " "))
}

func handleConn(conn net.Conn, c chan []byte, d chan bool) {
	defer close(c)
	defer func() { d <- true }()

	data := make([]byte, 1024)
	var buf bytes.Buffer

	for {
		n, err := conn.Read(data)
		if err != nil {
			if err != io.EOF {
				fmt.Printf("Error reading from connection: %v\n", err)
			}
			return
		}
		if n == 0 {
			return
		}

		buf.Write(data[:n])
		if idx := bytes.IndexByte(buf.Bytes(), '\n'); idx != -1 {
			data = hack(buf.Bytes())
			c <- data
			buf.Next(idx + 1)
		}
	}
}

func handleClient(clientConn net.Conn) {
	defer clientConn.Close()

	// Connect to the upstream server
	serverConn, err := net.Dial("tcp", "chat.protohackers.com:16963")
	//serverConn, err := net.Dial("tcp", "localhost:3030")
	if err != nil {
		fmt.Println("Failed to connect to upstream server:", err)
		return
	}
	defer serverConn.Close()

	clientToServer := make(chan []byte)
	serverToClient := make(chan []byte)
	clientDisconnect := make(chan bool)
	serverDisconnect := make(chan bool)

	go handleConn(clientConn, clientToServer, clientDisconnect)
	go handleConn(serverConn, serverToClient, serverDisconnect)

	go func() {
		for {
			select {
			case data, ok := <-clientToServer:
				if !ok {
					return
				}
				_, err := serverConn.Write(data)
				if err != nil {
					fmt.Println("error writing to server: ", err)
				}
			case data, ok := <-serverToClient:
				if !ok {
					return
				}
				_, err := clientConn.Write(data)
				if err != nil {
					fmt.Println("error writing to server: ", err)
				}
			}
		}
	}()

	// Wait for a disconnect
	select {
	case <-clientDisconnect:
	case <-serverDisconnect:
	}
}

func main() {
	listener, err := net.Listen("tcp", ":3030")
	//listener, err := net.Listen("tcp", ":3031")
	if err != nil {
		fmt.Println("Failed to start listener:", err)
		return
	}
	defer listener.Close()

	for {
		clientConn, err := listener.Accept()
		if err != nil {
			fmt.Println("Failed to accept client connection:", err)
			continue
		}
		go handleClient(clientConn)
	}
}