gamestatus/java/java.go

package java

import (
	"bytes"
	"context"
	"crypto/tls"
	"encoding/binary"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net"
	"strconv"
	"strings"
	"time"

	"github.com/VexoraDevelopment/mcstatus/info"
)

type Options struct {
	Timeout   time.Duration
	EnableSRV bool
	Resolver  *net.Resolver

	UseTLS    bool
	TLSConfig *tls.Config
}

type Client struct {
	opt Options
}

func New(opt Options) *Client {
	if opt.Timeout <= 0 {
		opt.Timeout = 2 * time.Second
	}
	if opt.Resolver == nil {
		opt.Resolver = net.DefaultResolver
	}
	return &Client{opt: opt}
}

func (c *Client) Connect(address string, port int) (*info.ServerInfo, error) {
	if port == 0 {
		port = 25565
	}

	host := address
	p := port

	if c.opt.EnableSRV && net.ParseIP(host) == nil {
		if rh, rp, err := c.resolveSRV(host); err == nil && rh != "" {
			host = rh
			if rp != 0 {
				p = rp
			}
		}
	}

	return c.Status(host, p)
}

func (c *Client) Status(address string, port int) (*info.ServerInfo, error) {
	conn, err := c.dial(address, port)
	if err != nil {
		return nil, err
	}
	defer conn.Close()

	_ = conn.SetDeadline(time.Now().Add(c.opt.Timeout))

	const protocolVersion = 47

	if err := writePacket(conn, func(w *bytes.Buffer) {
		writeVarInt(w, 0x00)
		writeVarInt(w, protocolVersion)
		writeString(w, address)
		writeU16(w, uint16(port))
		writeVarInt(w, 1)
	}); err != nil {
		return nil, err
	}

	if err := writePacket(conn, func(w *bytes.Buffer) {
		writeVarInt(w, 0x00)
	}); err != nil {
		return nil, err
	}

	pkt, err := readPacket(conn)
	if err != nil {
		return nil, err
	}
	r := bytes.NewReader(pkt)

	pid, err := readVarInt(r)
	if err != nil {
		return nil, err
	}
	if pid != 0x00 {
		return nil, fmt.Errorf("unexpected status response packet id: %d", pid)
	}

	js, err := readString(r)
	if err != nil {
		return nil, err
	}

	latency, _ := measureLatency(conn)
	raw := json.RawMessage(js)
	parsed, err := parseJavaStatus(raw)
	if err != nil {
		return nil, err
	}

	ip := resolveIP(address)
	srvInfo := &info.ServerInfo{
		Edition:  info.EditionJava,
		Address:  address,
		IP:       ip,
		Port:     port,
		MOTD:     parsed.MOTD,
		Version:  parsed.VersionName,
		Software: parsed.VersionName,
		Online:   parsed.Online,
		Slots:    parsed.Max,
		Latency:  latency,
		Raw:      raw,
	}
	return srvInfo, nil
}

func (c *Client) resolveSRV(domain string) (string, int, error) {
	ctx, cancel := context.WithTimeout(context.Background(), c.opt.Timeout)
	defer cancel()

	_, addrs, err := c.opt.Resolver.LookupSRV(ctx, "minecraft", "tcp", domain)
	if err != nil || len(addrs) == 0 {
		return "", 0, errors.New("no _minecraft._tcp SRV record")
	}
	target := strings.TrimSuffix(addrs[0].Target, ".")
	return target, int(addrs[0].Port), nil
}

func (c *Client) dial(host string, port int) (net.Conn, error) {
	addr := net.JoinHostPort(host, strconv.Itoa(port))
	d := &net.Dialer{Timeout: c.opt.Timeout}

	if !c.opt.UseTLS {
		return d.Dial("tcp", addr)
	}

	cfg := c.opt.TLSConfig
	if cfg == nil {
		cfg = &tls.Config{ServerName: host}
	}
	return tls.DialWithDialer(d, "tcp", addr, cfg)
}

func writePacket(w io.Writer, build func(*bytes.Buffer)) error {
	var payload bytes.Buffer
	build(&payload)

	var framed bytes.Buffer
	writeVarInt(&framed, payload.Len())
	_, _ = framed.Write(payload.Bytes())

	_, err := w.Write(framed.Bytes())
	return err
}

func readPacket(r io.Reader) ([]byte, error) {
	length, err := readVarIntFromIO(r)
	if err != nil {
		return nil, err
	}
	if length < 0 || length > 1<<20 {
		return nil, fmt.Errorf("invalid packet length: %d", length)
	}

	buf := make([]byte, length)
	if _, err := io.ReadFull(r, buf); err != nil {
		return nil, err
	}
	return buf, nil
}

func writeVarInt(w *bytes.Buffer, v int) {
	uv := uint32(v)
	for {
		if (uv & ^uint32(0x7F)) == 0 {
			_ = w.WriteByte(byte(uv))
			return
		}
		_ = w.WriteByte(byte(uv&0x7F | 0x80))
		uv >>= 7
	}
}

func readVarInt(r *bytes.Reader) (int, error) {
	var numRead int
	var result int
	for {
		if numRead > 5 {
			return 0, errors.New("varint too big")
		}
		b, err := r.ReadByte()
		if err != nil {
			return 0, err
		}
		value := int(b & 0x7F)
		result |= value << (7 * numRead)
		numRead++
		if (b & 0x80) == 0 {
			break
		}
	}
	return result, nil
}

func readVarIntFromIO(r io.Reader) (int, error) {
	var numRead int
	var result int
	var one [1]byte

	for {
		if numRead > 5 {
			return 0, errors.New("varint too big")
		}
		if _, err := io.ReadFull(r, one[:]); err != nil {
			return 0, err
		}
		b := one[0]
		value := int(b & 0x7F)
		result |= value << (7 * numRead)
		numRead++
		if (b & 0x80) == 0 {
			break
		}
	}
	return result, nil
}

func writeString(w *bytes.Buffer, s string) {
	writeVarInt(w, len(s))
	_, _ = w.WriteString(s)
}

func readString(r *bytes.Reader) (string, error) {
	n, err := readVarInt(r)
	if err != nil {
		return "", err
	}
	if n < 0 || n > 1<<20 {
		return "", fmt.Errorf("invalid string length: %d", n)
	}
	b := make([]byte, n)
	if _, err := io.ReadFull(r, b); err != nil {
		return "", err
	}
	return string(b), nil
}

func writeU16(w *bytes.Buffer, v uint16) {
	var tmp [2]byte
	binary.BigEndian.PutUint16(tmp[:], v)
	_, _ = w.Write(tmp[:])
}

func measureLatency(conn net.Conn) (time.Duration, error) {
	start := time.Now()
	ts := time.Now().UnixMilli()

	if err := writePacket(conn, func(w *bytes.Buffer) {
		writeVarInt(w, 0x01)
		var tmp [8]byte
		binary.BigEndian.PutUint64(tmp[:], uint64(ts))
		_, _ = w.Write(tmp[:])
	}); err != nil {
		return 0, err
	}

	pkt, err := readPacket(conn)
	if err != nil {
		return 0, err
	}

	r := bytes.NewReader(pkt)
	pid, err := readVarInt(r)
	if err != nil {
		return 0, err
	}
	if pid != 0x01 {
		return 0, fmt.Errorf("unexpected pong packet id: %d", pid)
	}

	return time.Since(start), nil
}

type javaStatusParsed struct {
	VersionName string
	Online      int
	Max         int
	MOTD        string
}

func parseJavaStatus(raw json.RawMessage) (*javaStatusParsed, error) {
	var doc map[string]any
	if err := json.Unmarshal(raw, &doc); err != nil {
		return nil, err
	}

	out := &javaStatusParsed{}

	if v, ok := doc["version"].(map[string]any); ok {
		if name, _ := v["name"].(string); name != "" {
			out.VersionName = name
		}
	}

	if p, ok := doc["players"].(map[string]any); ok {
		out.Online = asInt(p["online"])
		out.Max = asInt(p["max"])
	}

	out.MOTD = parseDescription(doc["description"])
	return out, nil
}

func parseDescription(v any) string {
	switch t := v.(type) {
	case string:
		return t
	case map[string]any:
		if s, _ := t["text"].(string); s != "" {
			return s
		}
		if extra, ok := t["extra"].([]any); ok {
			var b strings.Builder
			for _, it := range extra {
				if m, ok := it.(map[string]any); ok {
					if s, _ := m["text"].(string); s != "" {
						b.WriteString(s)
					}
				}
			}
			if b.Len() > 0 {
				return b.String()
			}
		}
	}
	return ""
}

func asInt(v any) int {
	switch t := v.(type) {
	case float64:
		return int(t)
	case int:
		return t
	case json.Number:
		n, _ := t.Int64()
		return int(n)
	default:
		return 0
	}
}

func resolveIP(host string) string {
	if ip := net.ParseIP(host); ip != nil {
		return ip.String()
	}
	ips, err := net.LookupIP(host)
	if err != nil || len(ips) == 0 {
		return ""
	}
	return ips[0].String()
}