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decoder.go
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decoder.go
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package tl
import (
"bytes"
"encoding/binary"
"encoding/hex"
"fmt"
"io"
"reflect"
)
type SumType string
func Unmarshal(r io.Reader, o any) error {
return decode(r, reflect.ValueOf(o))
}
type UnmarshalerTL interface {
UnmarshalTL(r io.Reader) error
}
func decode(buf io.Reader, val reflect.Value) error {
if val.Kind() == reflect.Pointer {
val = val.Elem()
}
i, ok := reflect.New(val.Type()).Interface().(UnmarshalerTL)
if ok {
err := i.UnmarshalTL(buf)
if err != nil {
return err
}
val.Set(reflect.ValueOf(i).Elem())
return nil
}
if !val.CanSet() {
return fmt.Errorf("value can't be changed")
}
switch val.Kind() {
case reflect.Uint32, reflect.Int32:
b := make([]byte, 4)
_, err := io.ReadFull(buf, b)
if err != nil {
return err
}
if val.Kind() == reflect.Uint32 {
val.SetUint(uint64(binary.LittleEndian.Uint32(b)))
} else {
val.SetInt(int64(binary.LittleEndian.Uint32(b)))
}
return nil
case reflect.Uint64, reflect.Int64:
b := make([]byte, 8)
_, err := io.ReadFull(buf, b)
if err != nil {
return err
}
if val.Kind() == reflect.Uint64 {
val.SetUint(binary.LittleEndian.Uint64(b))
} else {
val.SetInt(int64(binary.LittleEndian.Uint64(b)))
}
return nil
case reflect.Bool:
b := make([]byte, 4)
_, err := io.ReadFull(buf, b)
if err != nil {
return err
}
switch binary.LittleEndian.Uint32(b) {
case 0x997275b5:
val.SetBool(true)
case 0xbc799737:
val.SetBool(false)
default:
return fmt.Errorf("invalid Bool tag")
}
return nil
case reflect.Slice:
if val.Type().Elem().Kind() != reflect.Uint8 {
return decodeVector(buf, val)
}
data, err := readByteSlice(buf)
if err != nil {
return err
}
val.SetBytes(data)
return nil
case reflect.String:
data, err := readByteSlice(buf)
if err != nil {
return err
}
val.SetString(string(data))
return nil
case reflect.Array:
if val.Type().Elem().Kind() != reflect.Uint8 {
return fmt.Errorf("decoding array of %v not supported", val.Type().Elem().Kind())
}
data, err := readByteSlice(buf)
if err != nil {
return err
}
if val.Type().Len() != len(data) {
return fmt.Errorf("mismatched lenghth of decoded byte slice (%v) and array (%v)", len(data), val.Type().Len())
}
reflect.Copy(val, reflect.ValueOf(data))
return nil
case reflect.Struct:
return decodeStruct(buf, val)
default:
return fmt.Errorf("type %v not implemented", val.Kind())
}
}
func readByte(r io.Reader) (byte, error) {
var b [1]byte
_, err := io.ReadFull(r, b[:])
return b[0], err
}
func readByteSlice(r io.Reader) ([]byte, error) {
firstByte, err := readByte(r)
if err != nil {
return nil, err
}
var data []byte
var full int
if firstByte < 254 {
data = make([]byte, int(firstByte))
_, err := io.ReadFull(r, data)
if err != nil {
return nil, err
}
full = 1 + len(data)
} else if firstByte == 254 {
sizeBuf := make([]byte, 4)
_, err := io.ReadFull(r, sizeBuf[:3])
if err != nil {
return nil, err
}
data = make([]byte, binary.LittleEndian.Uint32(sizeBuf))
_, err = io.ReadFull(r, data)
if err != nil {
return nil, err
}
full = 4 + len(data)
} else {
return nil, fmt.Errorf("invalid bytes prefix")
}
for ; full%4 != 0; full++ {
_, err = readByte(r)
if err != nil {
return nil, err
}
}
return data, nil
}
func decodeStruct(buf io.Reader, val reflect.Value) error {
if _, ok := val.Type().FieldByName("SumType"); ok {
return decodeSumType(buf, val)
} else {
return decodeBasicStruct(buf, val)
}
}
func decodeSumType(r io.Reader, val reflect.Value) error {
var tagBytes [4]byte
_, err := io.ReadFull(r, tagBytes[:])
if err != nil {
return err
}
for i := 0; i < val.NumField(); i++ {
if !val.Field(i).CanSet() {
return fmt.Errorf("can't set field %v", i)
}
if val.Field(i).Type().Name() == "SumType" {
continue
}
tag := val.Type().Field(i).Tag.Get("tlSumType")
ok, err := compareWithTag(tagBytes, tag)
if err != nil {
return err
}
if ok {
val.FieldByName("SumType").SetString(val.Type().Field(i).Name)
err := decode(r, val.Field(i))
if err != nil {
return err
}
return nil
}
}
return fmt.Errorf("can not decode sumtype")
}
func decodeBasicStruct(r io.Reader, val reflect.Value) error {
for i := 0; i < val.NumField(); i++ {
if !val.Field(i).CanSet() {
return fmt.Errorf("can't set field %v", i)
}
err := decode(r, val.Field(i))
if err != nil {
return err
}
}
return nil
}
func compareWithTag(tagBytes [4]byte, tag string) (bool, error) {
t, err := hex.DecodeString(tag)
if err != nil {
return false, err
}
if len(t) != 4 {
return false, fmt.Errorf("invalid tag")
}
return bytes.Equal([]byte{t[3], t[2], t[1], t[0]}, tagBytes[:]), nil
}
func decodeVector(r io.Reader, val reflect.Value) error {
var b [4]byte
_, err := io.ReadFull(r, b[:])
if err != nil {
return err
}
ln := int(binary.LittleEndian.Uint32(b[:]))
item := reflect.New(val.Type().Elem())
slice := reflect.MakeSlice(val.Type(), 0, ln)
for i := 0; i < ln; i++ {
err := decode(r, item)
slice = reflect.Append(slice, item.Elem())
if err != nil {
return err
}
}
val.Set(slice)
return nil
}