mineauth/server/server.go

package server

import (
	"bytes"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	_ "embed"
	"encoding/json"
	"fmt"
	"io"
	gonet "net"
	"os"
	"os/exec"
	"strings"

	"github.com/Tnze/go-mc/chat"
	"github.com/Tnze/go-mc/net"
	pk "github.com/Tnze/go-mc/net/packet"
	"github.com/google/uuid"
	"github.com/rs/zerolog/log"
)

//go:embed favicon.png
var favicon []byte

type Server struct {
	privateKey *rsa.PrivateKey
	publicKey  []byte
	favicon    []byte
	opts       Options
}

type Options struct {
	CommunityURL string
	PingMessage  string
	FaviconPath  string
	Hooks        []string
}

func New(opts Options) (*Server, error) {
	private, err := rsa.GenerateKey(rand.Reader, 1024)
	if err != nil {
		return nil, fmt.Errorf("error generate private key: %v", err)
	}

	public, err := x509.MarshalPKIXPublicKey(private.Public())
	if err != nil {
		return nil, fmt.Errorf("error form public key to PKIX, ASN.1 DER: %v", err)
	}

	private.Precompute()

	icon := favicon
	if opts.FaviconPath != "" {
		fi, err := os.Open(opts.FaviconPath)
		if err != nil {
			return nil, err
		}
		defer fi.Close()
		icon, err = io.ReadAll(fi)
		if err != nil {
			return nil, err
		}
	}

	return &Server{
		privateKey: private,
		publicKey:  public,
		favicon:    icon,
		opts:       opts,
	}, nil
}

func (s *Server) Start(port int) error {
	l, err := net.ListenMC(fmt.Sprintf(":%d", port))
	if err != nil {
		return fmt.Errorf("listen error: %v", err)
	}

	for {
		conn, err := l.Accept()
		if err != nil {
			log.Err(err).Msg("accept error")
		}
		go s.acceptConn(conn)
	}
}

func (s *Server) acceptConn(conn net.Conn) {
	defer conn.Close()
	// handshake
	_, intention, err := s.handshake(conn)
	if err != nil {
		log.Err(err).Msg("handshake error")
		return
	}

	switch intention {
	default:
		log.Err(err).Msg("unknown handshake intention")
	case 1:
		s.acceptListPing(conn)
	case 2:
		s.handlePlaying(conn)
	}
}

func (s *Server) handlePlaying(conn net.Conn) {
	info, err := s.acceptLogin(conn)
	if err != nil {
		log.Err(err).Msg("login failed")
		return
	}

	verify, err := s.encryptionRequest(conn)
	if err != nil {
		log.Err(err).Msg("could not send encryption request")
		return
	}

	profile, secret, err := s.encryptionResponse(conn, info.Name, verify)
	if err != nil {
		log.Err(err).Msg("could not get encryption response")
		return
	}

	profile.IP, _, err = gonet.SplitHostPort(conn.Socket.RemoteAddr().String())
	if err != nil {
		log.Err(err).Msg("could not get user IP")
		return
	}

	payload, err := json.Marshal(profile)
	if err != nil {
		log.Err(err).Msg("could not marshal payload")
		return
	}

	for _, hook := range s.opts.Hooks {
		go func(h string) {
			s := strings.Split(h, " ")
			var args []string
			if len(s) > 1 {
				args = s[1:]
			}
			cmd := exec.Command(s[0], args...)
			cmd.Stdin = bytes.NewReader(payload)
			out, err := cmd.CombinedOutput()
			if err != nil {
				log.Err(err).Str("hook", h).Str("output", string(out)).Msg("could not run hook")
			}
		}(hook)
	}

	econn, err := encryptedConn(conn, secret)
	if err != nil {
		log.Err(err).Msg("could not create encrypted connection")
		return
	}

	msg := fmt.Sprintf("Thanks for authenticating, %s!", profile.Name)
	if s.opts.CommunityURL != "" {
		msg += fmt.Sprintf("\n\nJoin the community\n%s", s.opts.CommunityURL)
	}
	packet := pk.Marshal(0x00,
		chat.Message{Text: msg},
	)
	if err := packet.Pack(econn, 0); err != nil {
		log.Err(err).Msg("could not disconnect player")
	}
}

type PlayerInfo struct {
	Name    string
	UUID    uuid.UUID
	OPLevel int
}

// acceptLogin check player's account
func (s *Server) acceptLogin(conn net.Conn) (info PlayerInfo, err error) {
	//login start
	var p pk.Packet
	err = conn.ReadPacket(&p)
	if err != nil {
		return
	}

	err = p.Scan((*pk.String)(&info.Name)) //decode username as pk.String
	if err != nil {
		return
	}

	return
}

// handshake receive and parse Handshake packet
func (s *Server) handshake(conn net.Conn) (protocol, intention int32, err error) {
	var (
		p                   pk.Packet
		Protocol, Intention pk.VarInt
		ServerAddress       pk.String        // ignored
		ServerPort          pk.UnsignedShort // ignored
	)
	// receive handshake packet
	if err = conn.ReadPacket(&p); err != nil {
		return
	}
	err = p.Scan(&Protocol, &ServerAddress, &ServerPort, &Intention)
	return int32(Protocol), int32(Intention), err
}