mcsrv/main.go

package main

import (
	"bufio"
	"crypto/rand"
	"crypto/rsa"
	"encoding/base64"
	"errors"
	"fmt"
	"github.com/google/uuid"
	"log"
	"net"
	"os"
	"reflect"
	"regexp"
	"strings"
	"time"
)

const (
	HOST                 = "127.0.0.2"
	PORT                 = "25565"
	TYPE                 = "tcp"
	ProtocolVersion      = 767
	VERSION              = "1.21.1"
	CompressionThreshold = -1
)

var maxPlayers int32
var icon string
var iconData []byte
var serverID = make([]byte, 20)

var serverPrivateKey *rsa.PrivateKey
var serverPublicKey *rsa.PublicKey

var usernameRegex = regexp.MustCompile("^[a-zA-Z0-9_]{3,16}$")

var world World

func readIcon(fileName string) (icon string) {
	var err error
	iconData, err = os.ReadFile(fileName)
	if err != nil {
		return
	}
	icon = "data:image/png;base64," + base64.StdEncoding.EncodeToString(iconData)
	return
}

func main() {
	maxPlayers = 200
	icon = readIcon("icon.png")

	world = World{
		Difficulty:       0,
		DifficultyLocked: false,
		Hardcore:         false,
		Dimensions: []Dimension{
			{
				ID:   0,
				Name: "minecraft:overworld",
			}, {
				ID:   1,
				Name: "minecraft:the_nether",
			},
			{
				ID:   2,
				Name: "minecraft:the_end",
			},
		},
		ViewDistance:        4,
		SimulationDistance:  4,
		ReducedDebugInfo:    false,
		EnableRespawnScreen: true,
		DoLimitedCrafting:   false,
		Seed:                uuid.New(),
		FeatureFlags:        []string{"minecraft:vanilla", "minecraft:bundle", "minecraft:trade_rebalance"},
		DataPacks: []DatapackInfo{{
			Namespace: "minecraft",
			ID:        "core",
			Version:   "1.21",
		}},
		ReportDetails: map[string]string{"I hate myself": "YES, REALLY"},
		ServerLinks: []ServerLink{{
			LabelString: "",
			LabelInt:    0,
			URL:         "https://brn.systems",
		}},
		TickRate: 20,
	}

	var err error
	//serverID, err = serverIDCreate()
	serverID = []byte("")

	if err != nil {
		log.Fatal(err)
	}
	serverPrivateKey, serverPublicKey, err = GenerateRSAKeyPair()
	if err != nil {
		return
	}

	listen, err := net.Listen(TYPE, HOST+":"+PORT)
	if err != nil {
		log.Fatal(err)
	}
	// close listener
	defer func(listen net.Listener) {
		err := listen.Close()
		if err != nil {
			log.Println(err)
		}
	}(listen)

	for {
		conn, err := listen.Accept()
		if err != nil {
			log.Fatal(err)
		}
		go handleRequest(conn)
	}
}

func handleRequest(conn net.Conn) {
	var errOut error
	var player = Player{
		state:                0,
		conn:                 conn,
		version:              0,
		requestedAddress:     "",
		requestedPort:        0,
		reader:               bufio.NewReader(conn),
		compressionThreshold: -1,
	}
	for {
		packetID, packetData, err := player.readPacket()
		if err != nil {
			errOut = err
			break
		}

		switch player.state {
		case 0: // Handshake state
			switch packetID {
			case 0x00:
				version, address, port, nextState, err := getHandshakePacket(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.version = version
				player.requestedAddress = address
				player.requestedPort = port
				player.state = nextState
				if player.state == 3 {
					player.state = 2
					player.transferred = true
				}

				world.Players = append(world.Players, player)
			default:
				errOut = fmt.Errorf("unexpected packet %x in handshake state", packetID)
				log.Println(errOut)
			}

		case 1: // Status state
			switch packetID {
			case 0x00:
				err := player.sendStatusResponse("Hello there")
				if err != nil {
					errOut = err
					break
				}
			case 0x01:
				payload, err := getPingPacket(packetData)
				if err != nil {
					errOut = err
					break
				}
				err = player.sendPongPacket(payload)
				if err != nil {
					errOut = err
					break
				}
			default:
				errOut = fmt.Errorf("unexpected packet %x in status state", packetID)
				log.Println(errOut)
			}

		case 2: // Login state
			switch packetID {
			case 0x00:
				username, playerUUID, err := getLoginStart(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.Entity.Name = username
				player.uuid = playerUUID
				if !usernameRegex.MatchString(player.Entity.Name) {
					errOut = errors.New("bad username")
					break
				}
				err = player.sendEncryptionRequest()
				if err != nil {
					errOut = err
					break
				}
			case 0x01:
				sharedSecretFromClient, verifyTokenFromClient, err := getEncryptionResponse(packetData)
				if err != nil {
					errOut = err
					break
				}
				decryptedVerifyTokenFromClient, err := rsa.DecryptPKCS1v15(rand.Reader, serverPrivateKey, verifyTokenFromClient)
				if err != nil {
					errOut = err
					break
				}
				if !reflect.DeepEqual(player.verifyToken, decryptedVerifyTokenFromClient) {
					errOut = errors.New("wrong session verify token")
					break
				}
				decryptedSecret, err := rsa.DecryptPKCS1v15(rand.Reader, serverPrivateKey, sharedSecretFromClient)
				if err != nil {
					errOut = err
					break
				}
				success, err := player.hasJoinedSession(decryptedSecret)
				if err != nil {
					errOut = err
					break
				}
				if !success {
					errOut = errors.New("joined session not found")
					break
				}
				if player.profile.ID != strings.Replace(player.uuid.String(), "-", "", -1) || player.profile.Name != player.Entity.Name {
					errOut = errors.New("wrong session name")
					break
				}
				player.encryptStream, player.decryptStream, err = NewCFB8Cipher(decryptedSecret)
				if err != nil {
					errOut = err
					break
				}
				err = player.sendCompression()
				if err != nil {
					errOut = err
					break
				}
				player.compressionThreshold = CompressionThreshold
				log.Println("sent compression")
				err = player.sendLoginSuccess()
				if err != nil {
					errOut = err
					break
				}
				log.Println("sent login success")
				err = player.sendDataPacks()
				if err != nil {
					errOut = err
					break
				}
				err = player.sendRegistryData()
				if err != nil {
					errOut = err
					break
				}
				err = player.sendFeatureFlags()
				if err != nil {
					errOut = err
					break
				}
				err = player.sendUpdateTags()
				if err != nil {
					errOut = err
					break
				}
				err = player.sendReportDetails()
				if err != nil {
					errOut = err
					break
				}
				err = player.sendServerLinks()
				if err != nil {
					errOut = err
					break
				}

			case 0x03:
				player.state = 3

			default:
				errOut = fmt.Errorf("unexpected packet %x in login state", packetID)
				log.Println(errOut)
			}

		case 3: //configuration
			switch packetID {
			case 0x00:
				locale, viewDistance, chatMode, chatColors, skinParts, isRightHanded, textFiltering, serverListing, err := getClientInformation(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.locale = locale
				player.viewDistance = viewDistance
				player.chatMode = chatMode
				player.chatColors = chatColors
				player.skinParts = skinParts
				player.isRightHanded = isRightHanded
				player.textFiltering = textFiltering
				player.serverListing = serverListing
			case 0x01:
				//TODO Implement cookie
			case 0x02:
				_, _, _ = getPluginPacket(packetData)
			case 0x03:
				player.state = 4
				go player.sendKeepAlives()
				err := player.sendPlayStart()
				if err != nil {
					errOut = err
					break
				}
				player.sendDifficulty()
				//player.send
			case 0x04:
				player.keepAliveReceivedTimestamp = time.Now().Unix()
			case 0x05:
				err := player.getPongPacket(packetData)
				if err != nil {
					errOut = err
					break
				}
			case 0x06:
				err := player.getResourcePackPacket(packetData)
				if err != nil {
					errOut = err
					break
				}
			case 0x07:
				err := player.getDataPacksPacket(packetData)
				if err != nil {
					errOut = err
					break
				}
			default:
				errOut = fmt.Errorf("unexpected packet %x in configration state", packetID)
				log.Println(errOut)
			}

		case 4:
			switch packetID {

			case 0x00: // Confirm Teleportation
				teleportID, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}
				// Handle teleport confirmation logic here
				if player.teleportID == teleportID {
					player.waitingForTeleportConfirm = false
				}

			case 0x01: // Query Block Entity Tag
				transactionID, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}
				var position BlockPosition
				err = position.receivePosition(packetData)
				if err != nil {
					errOut = err
					break
				}
				// Handle block entity query logic here
				//player.queryBlockEntityTag(transactionID, position)

			case 0x02: // Change Difficulty
				difficulty, err := packetData.ReadByte()
				if err != nil {
					errOut = err
					break
				}
				// Change difficulty logic, ensure player is an operator
				if player.PermissionLevel >= 2 {
					world.Difficulty = difficulty
					for _, iterPlayer := range world.Players {
						iterPlayer.sendDifficulty()
					}
				}

			case 0x03: // Acknowledge Message
				messageCount, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}
				// Acknowledge message logic here
				messageCount = messageCount
				//player.acknowledgeMessage(messageCount)

			case 0x04, 0x05: // Chat Command & Signed Chat Command
				command, err := receiveString(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.processChatCommand(command)

			case 0x06: // Chat Message
				message, err := receiveString(packetData)
				if err != nil {
					errOut = err
					break
				}
				_ = receiveInt64(packetData)
				_ = receiveInt64(packetData)
				// Handle the chat message here
				player.handleChatMessage(message)

			case 0x07: // Player Session
				//sessionId, err := receiveUUID(packetData)
				//if err != nil {
				//	errOut = err
				//	break
				//}
				//expiresAt := receiveInt64(packetData)
				//pubKeyLen, err := receiveVarint(packetData)
				//
				//maybe implement in the future

			case 0x08: // Chunk Batch Received
				_ = receiveFloat32(packetData) //chunks per tick

			case 0x09: // Client Status
				actionID, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}
				switch actionID {
				case 0:
					player.sendRespawn(true, true)
				case 1:
					player.sendAwardStatistics()
				}

			case 0x0A: // Client Information
				// Read Locale (16-character string)
				locale, err := receiveString(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.locale = locale

				// Read View Distance (1 byte)
				viewDistance, err := packetData.ReadByte()
				if err != nil {
					errOut = err
					break
				}
				player.viewDistance = int8(viewDistance)

				// Read Chat Mode (VarInt Enum)
				chatMode, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.chatMode = chatMode

				// Read Chat Colors (Boolean)
				chatColors, err := packetData.ReadByte()
				if err != nil {
					errOut = err
					break
				}
				player.chatColors = chatColors != 0

				// Read Displayed Skin Parts (Unsigned Byte)
				displayedSkinParts, err := packetData.ReadByte()
				if err != nil {
					errOut = err
					break
				}
				player.skinParts = displayedSkinParts

				// Read Main Hand (VarInt Enum)
				mainHand, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.isRightHanded = mainHand == 1

				// Read Enable Text Filtering (Boolean)
				enableTextFiltering, err := receiveBool(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.textFiltering = enableTextFiltering

				// Read Allow Server Listings (Boolean)
				allowServerListings, err := receiveBool(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.serverListing = allowServerListings

				// Successfully parsed the packet
				errOut = nil

			case 0x0B: // Command Suggestions Request
				transactionId, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}
				text, err := receiveString(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.requestCommandSuggestions(transactionId, text)

			case 0x0C: // Acknowledge Configuration
				player.state = 3

			case 0x0D: // Click Container Button
				windowID, err := packetData.ReadByte()
				if err != nil {
					errOut = err
					break
				}
				if windowID != player.WindowID {
					break
				}
				buttonID, err := packetData.ReadByte()
				if err != nil {
					errOut = err
					break
				}
				_ = buttonID
				//TODO implement logic

			case 0x0E: // Click Container
				// Parse fields and handle click container logic here
				windowID, err := packetData.ReadByte()
				if err != nil {
					errOut = err
					break
				}
				if windowID != player.WindowID {
					break
				}

				// Read StateID (VarInt)
				stateID, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}

				// Read Slot (Short)
				var slot int16
				slot = receiveInt16(packetData)
				if err != nil {
					errOut = err
					break
				}

				// Read Button (Byte)
				button, err := packetData.ReadByte()
				if err != nil {
					errOut = err
					break
				}

				// Read Mode (VarInt)
				mode, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}

				// Read number of ChangedSlots (VarInt)
				changedSlotsCount, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}

				var packet ClickContainerPacket

				// Initialize ChangedSlots slice
				packet.ChangedSlots = make([]Slot, changedSlotsCount)

				// Read each Slot in the ChangedSlots array
				for i := 0; i < int(changedSlotsCount); i++ {
					slotData, err := readSlot(data)
					if err != nil {
						errOut = err
						break
					}
					packet.ChangedSlots[i] = slotData
				}

				// Read CarriedItem (ItemStack)
				carriedItem, err := readSlot(data)
				if err != nil {
					errOut = err
					break
				}

				// Populate the packet struct
				packet.WindowID = windowID
				packet.StateID = stateID
				packet.Slot = slot
				packet.Button = int8(button)
				packet.Mode = mode
				packet.CarriedItem = carriedItem
				player.handleClickContainer(packet)

			case 0x0F: // Close Container
				windowID, err := packetData.ReadByte()
				if err != nil {
					errOut = err
					break
				}
				player.sendCloseContainer(windowID)

			case 0x10: // Change Container ItemStack State
				slotID, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}
				windowID, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}
				state, err := receiveBool(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.changeContainerSlotState(slotID, windowID, state)

			case 0x11: // Cookie Response
				key, err := receiveString(packetData)
				if err != nil {
					errOut = err
					break
				}
				hasPayload, err := receiveBool(packetData)
				if err != nil {
					errOut = err
					break
				}
				// Handle cookie response logic here
				player.handleCookieResponse(key, hasPayload)

			case 0x12: // Serverbound Plugin Message
				channel, err := receiveString(packetData)
				if err != nil {
					errOut = err
					break
				}
				data := packetData // Rest is the byte array
				player.handlePluginMessage(channel, data)

			case 0x13: // Debug Sample Subscription
				sampleType, err := receiveVarint(packetData)
				if err != nil {
					errOut = err
					break
				}
				player.subscribeToDebugSample(sampleType)

			case 0x14: // Edit Book
				// Parse fields and handle book editing logic
				player.handleEditBook(packetData)

			default:
				errOut = fmt.Errorf("unexpected packet %x in play state", packetID)
				log.Println(errOut)
			}

		default:
			errOut = fmt.Errorf("unknown player state %d", player.state)
			break
		}
		if errOut != nil {
			break
		}
	}

	if //goland:noinspection GoDfaConstantCondition
	errOut != nil {
		log.Println(errOut.Error())
		_ = player.sendDisconnect(fmt.Sprintf("Your server thread crashed: %s", errOut.Error()))
	}

	// Close connection
	err := conn.Close()
	if err != nil {
		log.Println(err)
	}
	for index, client := range world.Players {
		if player.conn == client.conn {
			world.Players = append(world.Players[:index], world.Players[index+1:]...)
			break
		}
	}
}