scanner.go

package main

import (
    "bytes"
    "net"
    "os"
    "os/exec"
    "time"
)

var filter = []byte("statusResponse")

func masscan() {
    path, err := exec.LookPath("masscan")
    if err != nil {
        panic(err)
    }

    time.Sleep(time.Duration(5 * time.Second))

    // $ sudo setcap cap_net_raw,cap_net_admin=eip /usr/bin/masscan
    // $ cat payload.txt
    // udp 28000-30000 "\xff\xff\xff\xffgetstatus"
    cmd := exec.Command(path, "-iL", "subnets.txt", "--ports", "U:28000-30000", "--source-port", "29070", "--max-rate", "1000000", "--nmap-payloads", "payload.txt", "--ttl", "130")
    if err := cmd.Run(); err != nil {
        panic(err)
    }

    os.Exit(0)
}

func handler(listener net.PacketConn, addr net.Addr, buffer []byte) {
    if bytes.Equal(buffer[4:18], filter) {
        players := bytes.Split(buffer, []byte("\n"))
        if len(players) >= 4 {
            println("[", addr.String(), "]")
            for _, v := range players[2 : len(players)-1] {
                pos := bytes.IndexRune(v, '"')
                println(string(v[pos:]))
            }
        } else {
            println(addr.String(), "server is empty")
        }
    }
}

func main() {
    listener, err := net.ListenPacket("udp4", "0.0.0.0:29070")
    if err != nil {
        panic(err)
    }
    defer listener.Close()

    go masscan()

    for {
        buffer := make([]byte, 2048)
        n, addr, err := listener.ReadFrom(buffer)
        if err != nil {
            continue
        }
        go handler(listener, addr, buffer[:n])
    }
}