minimcd/protocol/protocol.go

package protocol

import (
	"bytes"
	"encoding/binary"
	"encoding/json"
	"io"

	"golang.org/x/exp/constraints"
)

type intType interface {
	int | int32 | int64
}
type Var[T intType] []byte
type String []byte

const SEGMENT_BITS = 0x7F
const CONTINUE_BIT = 0x80

func ToVar[T intType](value T) Var[T] {
	ret := make(Var[T], 0)
	for {
		if (value & ^SEGMENT_BITS) == 0 {
			ret = append(ret, byte(value))
			return ret
		}
		ret = append(ret, byte((value&SEGMENT_BITS)|CONTINUE_BIT))
		value = T(uint(value) >> 7)
	}
}
func FromVar[T intType](x Var[T]) T {
	value, position := T(0), 0
	for i := 0; ; i++ {
		cur := x[i]
		value |= T((cur & SEGMENT_BITS) << byte(position))
		if (cur & CONTINUE_BIT) == 0 {
			break
		}
		position += 7
	}
	return value
}
func StreamedFromVarNoException[T intType](reader io.Reader) T {
	value, position := T(0), 0
	buf := make(Var[T], 1)
	for i := 0; ; i++ {
		reader.Read(buf)
		cur := buf[0]
		value |= (T(cur) & SEGMENT_BITS) << position
		if (cur & CONTINUE_BIT) == 0 {
			break
		}
		position += 7
	}
	return value
}
func ToString(str string) String {
	ret := make(String, 0)
	ret = append(ret, ToVar[int](len(str))...)
	ret = append(ret, []byte(str)...)
	return ret
}

func FromString(x String) string {
	l := FromVar(Var[int](x))
	ll := Length(Var[int](x))
	return string(x[ll : ll+l])
}
func StreamedFromStringNoException(reader io.Reader) string {
	l := StreamedFromVarNoException[int](reader)
	buf := make([]byte, l)
	reader.Read(buf)
	return string(buf)
}

type PrefixedArray[T intType | byte] []byte

func ToPrefixedArray[T intType | byte](arr []T) PrefixedArray[T] {
	ret := make(PrefixedArray[T], 0)
	ret = append(ret, ToVar[int](len(arr))...)
	switch any(*new(T)).(type) {
	case byte:
		for _, v := range arr {
			ret = append(ret, byte(v))
		}
	default:
		panic("unimplemented!")
	}
	return ret
}
func StreamedFromPrefixedArrayNoException(reader io.Reader) []byte { //I don't know how to write parser for other types, left for further change
	l := StreamedFromVarNoException[int](reader)
	ret := make([]byte, l)
	reader.Read(ret)
	return ret
}

type VarLengthTypes interface {
	Var[int] | Var[int32] | Var[int64] | String
}

// TODO: rewrite as method
func Length[T VarLengthTypes](x T) int {
	switch any(x).(type) {
	case Var[int], Var[int32], Var[int64]:
		i := 0
		for ; ; i++ {
			cur := x[i]
			if (cur & CONTINUE_BIT) == 0 {
				break
			}
		}
		return i + 1
	case String:
		return Length[Var[int]](Var[int](x)) + len(FromString(String(x)))
	default:
		panic("unreachable")
	}
}

type Boolean [4]byte

func ToBoolean(x bool) (ret Boolean) {
	if x {
		ret[3] = 1
	} else {
		ret[3] = 0
	}
	return
}
func StreamedFromBooleanNoException(reader io.Reader) bool {
	buf := Boolean{}
	reader.Read(buf[:])
	if buf[3] == 1 {
		return true
	} else {
		return false
	}
}

type BigEndian[T constraints.Integer] []byte

func ToBigEndian[T constraints.Integer](x T) BigEndian[T] {
	buf := new(bytes.Buffer)
	binary.Write(buf, binary.BigEndian, x)
	return buf.Bytes()
}
func FromBigEndian[T constraints.Integer](x BigEndian[T]) (ret T) {
	binary.Read(bytes.NewReader(x), binary.BigEndian, &ret)
	return
}
func StreamedFromBigEndianNoException[T constraints.Integer](reader io.Reader) (ret T) {
	buf := make(BigEndian[T], binary.Size(ret))
	reader.Read(buf)
	binary.Read(bytes.NewReader(buf), binary.BigEndian, &ret)
	return
}

type UUID [16]byte // I don't think that I should parse the UUID sent from server, which means the endianess will be kept the same

type Data []byte

func ToHandshakePacketData(ver int, addr string, port uint16, nxtst int) Data {
	ret := make(Data, 0)
	ret = append(ret, ToVar(ver)...)
	ret = append(ret, ToString(addr)...)
	ret = append(ret, ToBigEndian(port)...)
	ret = append(ret, ToVar(nxtst)...)
	return ret
}
func FromHandshakePacketData(x Data) (ver int, addr string, port uint16, nxtst int) {
	ver = FromVar(Var[int](x))
	x = x[Length(Var[int](x)):]
	addr = FromString(String(x))
	x = x[Length(String(x)):]
	port = FromBigEndian(BigEndian[uint16](x[:2]))
	x = x[2:]
	nxtst = FromVar(Var[int](x))
	return ver, addr, port, nxtst
}
func StreamedFromHandshakePacketDataNoException(reader io.Reader) (ver int, addr string, port uint16, nxtst int) {
	ver = StreamedFromVarNoException[int](reader)
	//x = x[Length(Var[int](x)):]
	addr = StreamedFromStringNoException(reader)
	// x = x[Length(String(x)):]
	port = StreamedFromBigEndianNoException[uint16](reader)
	// x = x[2:]
	nxtst = StreamedFromVarNoException[int](reader)
	return ver, addr, port, nxtst
}
func ToLoginStartPacketData(name string, uuid UUID) Data {
	ret := Data(ToString(name))
	ret = append(ret, uuid[:]...)
	return ret
}
func StreamedFromLoginStartPacketDataNoException(reader io.Reader) (name string, uuid UUID) {
	name = StreamedFromStringNoException(reader)
	reader.Read(uuid[:])
	return
}
func ToEncryptionRequestPacketData(sid string, pubkey []byte, token []byte, auth bool) Data {
	ret := make(Data, 0)
	ret = append(ret, ToString(sid)...)
	ret = append(ret, ToPrefixedArray(pubkey)...)
	ret = append(ret, ToPrefixedArray(token)...)
	authByte := ToBoolean(auth)
	ret = append(ret, authByte[:]...)
	return ret
}
func StreamedFromEncryptionRequestPacketData(reader io.Reader) (sid string, pubkey []byte, token []byte, auth bool) {
	sid = StreamedFromStringNoException(reader)
	pubkey = StreamedFromPrefixedArrayNoException(reader)
	token = StreamedFromPrefixedArrayNoException(reader)
	auth = StreamedFromBooleanNoException(reader)
	return
}

type disconnectJsonFields struct {
	Type string `json:"type"`
	Text string `json:"text"`
}

func ToDisconnectPacketData(text string) Data {
	ret, _ := json.Marshal(disconnectJsonFields{"text", text})
	return ret
}

type Packet []byte

func ToPacket(p int, data Data) Packet {
	ret := make(Packet, 0)
	pid := ToVar[int](p)
	ret = append(ret, ToVar[int](Length(pid)+len(data))...)
	ret = append(ret, pid...)
	ret = append(ret, data...)
	return ret
}
func StreamedFromPacketNoException(reader io.Reader) (int, Data) {
	l := StreamedFromVarNoException[int](reader)
	// ll := Length(Var[int](x))
	//pid := FromVar(Var[int](x[ll:]))
	pid := StreamedFromVarNoException[int](reader)
	ret := make(Data, l-Length(ToVar(pid)))
	reader.Read(ret)
	return pid, ret
}
func ToHandshakePacket(ver int, addr string, port uint16, nxtst int) Packet {
	return ToPacket(0x00, ToHandshakePacketData(ver, addr, port, nxtst))
}