mcstatus/client.go

package main

import (
	"bytes"
	"encoding/binary"
	"encoding/json"
	"fmt"
	"io"
	"net"
	"time"
)

type client struct {
	conn    net.Conn
	addr    string
	port    int
	version uint64
}

// newClient Initialises a new connection
func newClient(conn net.Conn, addr string, port int, ver uint64) client {
	return client{conn, addr, port, ver}
}

// read the response from the Minecraft server
func (c *client) read() (*Response, error) {
	buf := make([]byte, 0, 32768)
	tmp := make([]byte, 256)
	for {
		count, err := c.conn.Read(tmp)
		if count > 0 {
			buf = append(buf, tmp[:count]...)
		}
		if err != nil {
			if err == io.EOF {
				break
			} else {
				return nil, err
			}
		}
	}
	return c.handle(buf)
}

// write send handshake request to the Minecraft server
func (c *client) write() error {
	_, err := c.conn.Write(handshake(c.addr, c.port, c.version))
	if err != nil {
		return err
	}
	return nil
}

// handle parses response from Minecraft server and converts the json output to a protocol buffer
func (c *client) handle(message []byte) (*Response, error) {
	var response Response
	b := bytes.Split(message, []byte("{"))
	ne := bytes.SplitAfterN(message, b[0], 2)
	trim := bytes.TrimSuffix(ne[1], []byte("\x00"))
	if err := json.Unmarshal(trim, &response); err != nil {
		return nil, err
	}
	return &response, nil
}

// ping sends ping payload to Minecraft server
func (c *client) ping() (time.Duration, error) {
	start := time.Now()
	if _, err := c.conn.Write([]byte{0x01, byte(start.Unix())}); err != nil {
		return 0, err
	}
	buf := make([]byte, 2)
	for {
		fmt.Println("ping")
		_, err := c.conn.Read(buf)
		if err != nil {
			if err == io.EOF {
				break
			} else {
				return 0, err
			}
		}
	}
	return time.Since(start), nil
}

func (c *client) pingtest() (time.Duration, error) {
	start := time.Now()
	if _, err := c.conn.Write([]byte{0x01, byte(start.Unix())}); err != nil {
		return 0, err
	}
	_, err := io.ReadAll(c.conn)
	if err != nil {
		return 0, err
	}
	return time.Since(start), nil
}

/* handshake constructs the handshake packet to be sent to the Minecraft server
   see: https://wiki.vg/Server_List_Ping#Handshake */
func handshake(addr string, port int, ver uint64) []byte {
	id := []byte{0x00}
	state := []byte{0x01}

	version := make([]byte, 2)
	binary.PutUvarint(version, ver)
	p := make([]byte, 2)
	binary.BigEndian.PutUint16(p, uint16(port))
	length := packetlength(id, version, []byte(addr), p, state) + 1

	var handshake bytes.Buffer
	handshake.WriteByte(byte(length))
	handshake.Write(id)
	handshake.Write(version)
	handshake.WriteByte(byte(len(addr)))
	handshake.WriteString(addr)
	handshake.Write(p)
	handshake.Write(state)
	handshake.Write([]byte{0x01, 0x00})
	return handshake.Bytes()
}

func packetlength(b ...[]byte) (length int) {
	for _, bytes := range b {
		length += len(bytes)
	}
	return length
}