minerecon/packetcreator.go

package main

import (
	"bufio"
	"bytes"
	"compress/zlib"
	"crypto/md5"
	"encoding/binary"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"math"
	"strings"
	"time"
)

// Decompress function using zlib
func decompress(data []byte) ([]byte, error) {
	reader, err := zlib.NewReader(bytes.NewReader(data))
	if err != nil {
		return nil, err
	}
	defer func(reader io.ReadCloser) {
		_ = reader.Close()
	}(reader)

	var decompressedData bytes.Buffer
	_, err = io.Copy(&decompressedData, reader)
	if err != nil {
		return nil, err
	}

	return decompressedData.Bytes(), nil
}

// Compress function using zlib
func compress(data []byte) ([]byte, error) {
	var compressedData bytes.Buffer
	writer := zlib.NewWriter(&compressedData)

	_, err := writer.Write(data)
	if err != nil {
		return nil, err
	}

	err = writer.Close()
	if err != nil {
		return nil, err
	}

	return compressedData.Bytes(), nil
}

func readPacket(reader *bufio.Reader, threshold int32) (packetID int32, packetData []byte, packetLength int, err error) {
	packetLengthTemp, _, err := readVarint(reader)
	if err != nil {
		return
	}
	packetLength = packetLengthTemp

	packetData = make([]byte, packetLength)

	n, err := io.ReadFull(reader, packetData)
	if err != nil {
		return
	}
	if n != packetLength {
		err = errors.New("packet read length mismatch")
		return
	}

	var dataLength int
	if threshold > 0 {
		n, dataLengthTemp := receiveVarint(packetData)
		packetData = packetData[n:]
		dataLength = int(dataLengthTemp)
	}

	// If dataLength > 0, it means the packet is compressed
	if dataLength > 0 {
		packetData, err = decompress(packetData)
		if err != nil {
			return
		}
	}

	n, packetID = receiveVarint(packetData)
	packetLength -= n
	packetData = packetData[n:]

	return
}

func createPacket(packetID int32, packetData []byte, threshold int32, startedCompression bool) ([]byte, error) {
	var dataBuffer []byte
	addVarint(&dataBuffer, packetID)

	dataBuffer = append(dataBuffer, packetData...)

	var outBuffer []byte
	length := int32(len(dataBuffer))

	if startedCompression {
		if threshold > 0 && length >= threshold {
			// Compress the packet
			compressedData, err := compress(dataBuffer)
			if err != nil {
				return nil, err
			}
			dataBuffer = compressedData

			// Add the uncompressed length
			addVarint(&outBuffer, int32(len(packetData)))
		} else {
			// Set Data Length to 0 if not compressed
			addVarint(&outBuffer, 0)
		}
	}

	addVarint(&outBuffer, int32(len(dataBuffer)))

	// Append compressed or uncompressed data
	outBuffer = append(outBuffer, dataBuffer...)

	// Add the Packet Length

	return outBuffer, nil
}

func addString(buffer *[]byte, str string) {
	length := len(str)
	addVarint(buffer, int32(length))

	*buffer = append(*buffer, str...)
}

// Reads a VarInt from a bufio.Reader and returns the decoded value, the length read, and an error if any.
// Only negative values are transformed similar to Java's implementation.
func readVarint(r *bufio.Reader) (value int, length int, err error) {
	var position uint
	value = 0
	for {
		currentByte, err := r.ReadByte()
		if err != nil {
			return 0, length, err
		}
		value |= int(currentByte&0x7F) << position
		length++
		if (currentByte & 0x80) == 0 {
			break
		}
		position += 7
		if position >= 32 {
			return 0, length, fmt.Errorf("VarInt is too big")
		}
	}
	return value, length, nil
}

// Decodes a VarInt from the byte slice.
// This function handles the decoding in a manner similar to Java's VarInt,
// correctly managing positive and negative values.
func receiveVarint(b []byte) (currentOffset int, value int32) {
	var shift uint
	for {
		byteValue := b[currentOffset]
		currentOffset++
		value |= int32(byteValue&0x7F) << shift
		if (byteValue & 0x80) == 0 {
			// Apply sign extension for negative values
			break
		}
		shift += 7
		if shift >= 32 {
			panic("VarInt is too big")
		}
	}
	return
}

func addVarint(buffer *[]byte, value int32) {
	for {
		// Extract the lower 7 bits of the value
		temp := byte(value & 0x7F)
		value >>= 7

		// If the value is not zero or if there are more bytes to encode
		if value != 0 && value != -1 {
			temp |= 0x80 // Set the continuation bit
		} else {
			temp &= 0x7F // Clear the continuation bit if we're done
		}

		// Append the byte to the buffer
		addByte(buffer, temp)

		// Break the loop if no more continuation bit is set
		if (temp & 0x80) == 0 {
			break
		}
	}
}

func addVarlong(buffer *[]byte, value int64) {
	for {
		temp := byte(value & 0x7F) // Get the last 7 bits
		value >>= 7
		if value != 0 && value != -1 {
			temp |= 0x80 // Set the continuation bit
		}
		addByte(buffer, temp)
		if temp&0x80 == 0 {
			break
		}
	}
}

// Decodes a VarLong from the byte slice.
func receiveVarlong(b []byte) (currentOffset int, value int64) {
	var shift uint
	for {
		byteValue := b[currentOffset]
		currentOffset++
		value |= int64(byteValue&0x7F) << shift
		if (byteValue & 0x80) == 0 {
			// Sign extension for negative values
			if shift < 32 {
				value |= -1 << shift
			}
			break
		}
		shift += 7
		if shift >= 32 {
			panic("VarLong is too big")
		}
	}
	return
}

func addByte(buffer *[]byte, byte byte) {
	*buffer = append(*buffer, byte)
}

func receiveBool(buffer []byte) (currentOffset int, boolean bool) {
	boolean = buffer[0] == 1
	currentOffset = 1
	return
}

func addBool(buffer *[]byte, bool bool) {
	var boolByte byte
	boolByte = 0x00
	if bool {
		boolByte = 0x01
	}
	*buffer = append(*buffer, boolByte)
}

func constructOfflinePlayerUUID(username string) (dataArray []byte) {
	data := md5.Sum([]byte("OfflinePlayer:" + username))
	dataArray = data[:]

	// Set the version to 3 -> Name based md5 hash
	dataArray[6] = (dataArray[6] & 0x0f) | 0x30
	// IETF variant
	dataArray[8] = (dataArray[8] & 0x3f) | 0x80

	return dataArray
}

func createOfflineLoginPacket(username string, threshold int32) (outBuffer []byte, err error) {
	addString(&outBuffer, username)
	outBuffer = append(outBuffer, constructOfflinePlayerUUID(username)...)
	outBuffer, err = createPacket(0, outBuffer, threshold, false)
	return
}

func createClientBrandPacket(brand string, threshold int32, startedCompression bool) (outBuffer []byte, err error) {
	addString(&outBuffer, "minecraft:brand")
	addString(&outBuffer, brand)
	outBuffer, err = createPacket(2, outBuffer, threshold, startedCompression)
	return
}

func createConfirmLoginPacket(threshold int32, startedCompression bool) (packet []byte, err error) {
	packet, err = createPacket(3, []byte{}, threshold, startedCompression)
	return
}

func createStatusRequestPacket(threshold int32) (packet []byte, err error) {
	packet, err = createPacket(0, []byte{}, threshold, false)
	return
}

func addUint16(buffer *[]byte, value uint16) {
	*buffer = binary.BigEndian.AppendUint16(*buffer, value)
}

func addInt64(buffer *[]byte, value int64) {
	*buffer = binary.BigEndian.AppendUint64(*buffer, uint64(value))
}

func receiveFloat32(b []byte) (currentOffset int, value float32) {
	value = math.Float32frombits(binary.BigEndian.Uint32(b))
	currentOffset = binary.Size(value)
	return
}

func receiveFloat64(b []byte) (currentOffset int, value float64) {
	value = math.Float64frombits(binary.BigEndian.Uint64(b))
	currentOffset = binary.Size(value)
	return
}

func receiveInt32(b []byte) (currentOffset int, value int32) {
	value = int32(binary.BigEndian.Uint32(b))
	currentOffset = binary.Size(value)
	return
}

func receiveInt64(b []byte) (currentOffset int, value int64) {
	value = int64(binary.BigEndian.Uint64(b))
	currentOffset = binary.Size(value)
	return
}

func receiveByte(b []byte) (currentOffset int, value byte) {
	value = b[0]
	currentOffset = binary.Size(value)
	return
}

func receivePosition(b []byte) (currentOffset int, position Position) {
	encoded := binary.BigEndian.Uint64(b)
	x, y, z := DecodePosition(encoded)
	position = Position{X: x, Y: y, Z: z}
	currentOffset = binary.Size(encoded)
	return
}

func DecodePosition(encoded uint64) (x int32, y int16, z int32) {
	// Extract x, y, z from encoded value
	x = int32((encoded >> 38) & 0x3FFFFFF)
	y = int16(encoded & 0xFFF)
	z = int32((encoded >> 12) & 0x3FFFFFF)

	// Adjust for sign
	if x >= 1<<25 {
		x -= 1 << 26
	}
	if y >= 1<<11 {
		y -= 1 << 12
	}
	if z >= 1<<25 {
		z -= 1 << 26
	}

	return
}

func createHandshakePacket(version int32, address string, port uint16, nextState int32, threshold int32) (outBuffer []byte, err error) {
	addVarint(&outBuffer, version)
	addString(&outBuffer, address)
	addUint16(&outBuffer, port)
	addVarint(&outBuffer, nextState)
	outBuffer, err = createPacket(0, outBuffer, threshold, false)
	return
}

func createTeleportConfirmPacket(teleportID int32, threshold int32, startedCompression bool) (outBuffer []byte, err error) {
	addVarint(&outBuffer, teleportID)
	outBuffer, err = createPacket(0, outBuffer, threshold, startedCompression)
	return
}

func receiveString(buf []byte) (currentOffset int, strOut string) {
	n, stringLen := receiveVarint(buf)
	currentOffset = n
	strOut = string(buf[currentOffset : currentOffset+int(stringLen)])
	currentOffset += int(stringLen)
	return
}

func receiveTextComponent(buf []byte) (currentOffset int, component TextComponent, err error) {
	currentOffset, jsonString := receiveString(buf)
	if strings.ContainsAny(jsonString, "") {
	}
	jsonDecoderText := json.NewDecoder(strings.NewReader(jsonString))
	err = jsonDecoderText.Decode(&component)
	if err != nil {
		err = nil
		component.Text = jsonString
		component.CleanText = cleanMinecraftFormatting(jsonString)
	}
	return
}

func createEnabledDatapacksPacket(datapacks []DatapackInfo, threshold int32, startedCompression bool) (outBuffer []byte, err error) {
	addVarint(&outBuffer, int32(len(datapacks)))
	for _, datapack := range datapacks {
		addString(&outBuffer, datapack.Namespace)
		addString(&outBuffer, datapack.ID)
		addString(&outBuffer, datapack.Version)
	}
	outBuffer, err = createPacket(0x07, outBuffer, threshold, startedCompression)
	return
}

func createChatMessagePacket(message string, threshold int32, startedCompression bool) (outBuffer []byte, err error) {
	addString(&outBuffer, message)
	addInt64(&outBuffer, time.Now().Unix())
	addInt64(&outBuffer, time.Now().Unix())
	addBool(&outBuffer, false)
	addVarint(&outBuffer, 0)
	addByte(&outBuffer, 0)
	addByte(&outBuffer, 0)
	addByte(&outBuffer, 0)
	outBuffer, err = createPacket(0x06, outBuffer, threshold, startedCompression)
	return
}

func decodeEnabledDatapacks(buf []byte) (currentOffset int, outPacks []DatapackInfo) {
	currentOffset, datapackCount := receiveVarint(buf)
	for i := 0; i < int(datapackCount); i++ {
		nextOffset, namespace := receiveString(buf[currentOffset:])
		currentOffset += nextOffset
		nextOffset, ID := receiveString(buf[currentOffset:])
		currentOffset += nextOffset
		nextOffset, version := receiveString(buf[currentOffset:])
		currentOffset += nextOffset
		enabledDatapack := DatapackInfo{
			Namespace: namespace,
			ID:        ID,
			Version:   version,
		}
		outPacks = append(outPacks, enabledDatapack)
	}
	return
}

func createClientInformationPacket(locale string, renderDistance byte, chatMode int32, colors bool, skinParts byte, mainLeftHand bool, textFiltering bool, serverListing bool, threshold int32, startedCompression bool) (outBuffer []byte, err error) {
	var mainHand int32
	if mainLeftHand {
		mainHand = 0
	} else {
		mainHand = 1
	}
	addString(&outBuffer, locale)
	addByte(&outBuffer, renderDistance)
	addVarint(&outBuffer, chatMode)
	addBool(&outBuffer, colors)
	addByte(&outBuffer, skinParts)
	addVarint(&outBuffer, mainHand)
	addBool(&outBuffer, textFiltering)
	addBool(&outBuffer, serverListing)
	outBuffer, err = createPacket(0, outBuffer, threshold, startedCompression)
	return
}