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decode.go
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decode.go
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package nbt
import (
"bytes"
"errors"
"fmt"
"go/ast"
"io"
"reflect"
"strings"
"sync"
"unicode/utf8"
)
// Decoder reads NBT objects from an NBT input stream.
type Decoder struct {
// Encoding is the variant to use for decoding the NBT passed. By default, the variant is set to
// NetworkLittleEndian, which is the variant used for network NBT.
Encoding Encoding
r *offsetReader
depth int
}
// NewDecoder returns a new Decoder for the input stream reader passed.
func NewDecoder(r io.Reader) *Decoder {
return &Decoder{Encoding: NetworkLittleEndian, r: newOffsetReader(r)}
}
// NewDecoderWithEncoding returns a new Decoder for the input stream reader passed with a specific encoding.
func NewDecoderWithEncoding(r io.Reader, encoding Encoding) *Decoder {
return &Decoder{Encoding: encoding, r: newOffsetReader(r)}
}
// Decode reads the next NBT object from the input stream and stores it into the pointer to an object passed.
// See the Unmarshal docs for the conversion between NBT tags to Go types.
func (d *Decoder) Decode(v interface{}) error {
val := reflect.ValueOf(v)
if val.Kind() != reflect.Ptr {
return NonPointerTypeError{ActualType: val.Type()}
}
tagType, tagName, err := d.tag()
if err != nil {
return err
}
return d.unmarshalTag(val.Elem(), tagType, tagName)
}
// Unmarshal decodes a slice of NBT data into a pointer to a Go values passed. Marshal will use the
// NetworkLittleEndian encoding by default. To use a specific encoding, use UnmarshalEncoding.
//
// The Go value passed must be a pointer to a value. Anything else will return an error before decoding.
// The following NBT tags are decoded in the Go value passed as such:
// TAG_Byte: byte/uint8(/interface{}) or bool
// TAG_Short: int16(/interface{})
// TAG_Int: int32(/interface{})
// TAG_Long: int64(/interface{})
// TAG_Float: float32(/interface{})
// TAG_Double: float64(/interface{})
// TAG_ByteArray: [...]byte(/interface{}) (The value must be a byte array, not a slice)
// TAG_String: string(/interface{})
// TAG_List: []interface{}(/interface{}) (The value type of the slice may vary. Depending on the type of
// values in the List tag, it might be of the type of any of the other tags, such as []int64.
// TAG_Compound: struct{...}/map[string]interface{}(/interface{})
// TAG_IntArray: [...]int32(/interface{}) (The value must be an int32 array, not a slice)
// TAG_LongArray: [...]int64(/interface{}) (The value must be an int64 array, not a slice)
//
// Unmarshal returns an error if the data is decoded into a struct and the struct does not have all fields
// that the matching TAG_Compound in the NBT has, in order to prevent the loss of data. For varying data, the
// data should be decoded into a map.
// Nil maps and slices are initialised and filled out automatically by Unmarshal.
//
// Unmarshal accepts struct fields with the 'nbt' struct tag. The 'nbt' struct tag allows setting the name of
// a field that some tag should be decoded in. Setting the struct tag to '-' means that field will never be
// filled by the decoding of the data passed.
func Unmarshal(data []byte, v interface{}) error {
return UnmarshalEncoding(data, v, NetworkLittleEndian)
}
// UnmarshalEncoding decodes a slice of NBT data into a pointer to a Go values passed using the NBT encoding
// passed. Its functionality is identical to that of Unmarshal, except that it allows a specific encoding.
func UnmarshalEncoding(data []byte, v interface{}, encoding Encoding) error {
buf := bytes.NewBuffer(data)
return (&Decoder{Encoding: encoding, r: &offsetReader{
Reader: buf,
ReadByte: buf.ReadByte,
Next: buf.Next,
}}).Decode(v)
}
// These types are initialised once and re-used for each Unmarshal call.
var stringType = reflect.TypeOf("")
var byteType = reflect.TypeOf(byte(0))
var int32Type = reflect.TypeOf(int32(0))
var int64Type = reflect.TypeOf(int64(0))
// fieldMapPool is used to store maps holding the fields of a struct. These maps are cleared each time they
// are put back into the pool, but are re-used simply so that they need not to be re-allocated each operation.
var fieldMapPool = sync.Pool{
New: func() interface{} {
return map[string]reflect.Value{}
},
}
// unmarshalTag decodes a tag from the decoder's input stream into the reflect.Value passed, assuming the tag
// has the type and name passed.
func (d *Decoder) unmarshalTag(val reflect.Value, tagType byte, tagName string) error {
switch tagType {
default:
return UnknownTagError{Off: d.r.off, TagType: tagType, Op: "Match"}
case tagEnd:
return UnexpectedTagError{Off: d.r.off, TagType: tagEnd}
case tagByte:
value, err := d.r.ReadByte()
if err != nil {
return BufferOverrunError{Op: "Byte"}
}
if val.Kind() != reflect.Uint8 {
if val.Kind() == reflect.Bool {
if value != 0 {
val.SetBool(true)
}
return nil
}
if val.Kind() == reflect.Interface && val.NumMethod() == 0 {
// Empty interface.
val.Set(reflect.ValueOf(value))
return nil
}
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
val.SetUint(uint64(value))
case tagInt16:
value, err := d.Encoding.Int16(d.r)
if err != nil {
return err
}
if val.Kind() != reflect.Int16 {
if val.Kind() == reflect.Interface && val.NumMethod() == 0 {
// Empty interface.
val.Set(reflect.ValueOf(value))
return nil
}
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
val.SetInt(int64(value))
case tagInt32:
value, err := d.Encoding.Int32(d.r)
if err != nil {
return err
}
if val.Kind() != reflect.Int32 {
if val.Kind() == reflect.Interface && val.NumMethod() == 0 {
// Empty interface.
val.Set(reflect.ValueOf(value))
return nil
}
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
val.SetInt(int64(value))
case tagInt64:
value, err := d.Encoding.Int64(d.r)
if err != nil {
return err
}
if val.Kind() != reflect.Int64 {
if val.Kind() == reflect.Interface && val.NumMethod() == 0 {
// Empty interface.
val.Set(reflect.ValueOf(value))
return nil
}
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
val.SetInt(value)
case tagFloat32:
value, err := d.Encoding.Float32(d.r)
if err != nil {
return err
}
if val.Kind() != reflect.Float32 {
if val.Kind() == reflect.Interface && val.NumMethod() == 0 {
// Empty interface.
val.Set(reflect.ValueOf(value))
return nil
}
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
val.SetFloat(float64(value))
case tagFloat64:
value, err := d.Encoding.Float64(d.r)
if err != nil {
return err
}
if val.Kind() != reflect.Float64 {
if val.Kind() == reflect.Interface && val.NumMethod() == 0 {
// Empty interface.
val.Set(reflect.ValueOf(value))
return nil
}
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
val.SetFloat(value)
case tagString:
value, err := d.Encoding.String(d.r)
if err != nil {
return err
}
if !utf8.ValidString(value) {
return InvalidStringError{Off: d.r.off, String: value, Err: errors.New("string does not exist out of utf8 only")}
}
if val.Kind() != reflect.String {
if val.Kind() == reflect.Interface && val.NumMethod() == 0 {
// Empty interface.
val.Set(reflect.ValueOf(value))
return nil
}
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
val.SetString(value)
case tagByteArray:
length, err := d.Encoding.Int32(d.r)
if err != nil {
return err
}
data, err := consumeN(int(length), d.r)
if err != nil {
return BufferOverrunError{Op: "ByteArray"}
}
value := reflect.New(reflect.ArrayOf(int(length), byteType)).Elem()
for i := int32(0); i < length; i++ {
value.Index(int(i)).SetUint(uint64(data[i]))
}
if val.Kind() != reflect.Array {
if val.Kind() == reflect.Interface && val.NumMethod() == 0 {
// Empty interface.
val.Set(value)
return nil
}
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
if val.Cap() != int(length) {
return InvalidArraySizeError{Off: d.r.off, Op: "ByteArray", GoLength: val.Cap(), NBTLength: int(length)}
}
val.Set(value)
case tagInt32Array:
length, err := d.Encoding.Int32(d.r)
if err != nil {
return err
}
value := reflect.New(reflect.ArrayOf(int(length), int32Type)).Elem()
for i := int32(0); i < length; i++ {
v, err := d.Encoding.Int32(d.r)
if err != nil {
return err
}
value.Index(int(i)).SetInt(int64(v))
}
if val.Kind() != reflect.Array || val.Type().Elem().Kind() != reflect.Int32 {
if val.Kind() == reflect.Interface && val.NumMethod() == 0 {
// Empty interface.
val.Set(value)
return nil
}
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
if val.Cap() != int(length) {
return InvalidArraySizeError{Off: d.r.off, Op: "Int32Array", GoLength: val.Cap(), NBTLength: int(length)}
}
val.Set(value)
case tagInt64Array:
length, err := d.Encoding.Int32(d.r)
if err != nil {
return err
}
value := reflect.New(reflect.ArrayOf(int(length), int64Type)).Elem()
for i := int32(0); i < length; i++ {
v, err := d.Encoding.Int64(d.r)
if err != nil {
return err
}
value.Index(int(i)).SetInt(v)
}
if val.Kind() != reflect.Array || val.Type().Elem().Kind() != reflect.Int64 {
if val.Kind() == reflect.Interface && val.NumMethod() == 0 {
// Empty interface.
val.Set(value)
return nil
}
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
if val.Cap() != int(length) {
return InvalidArraySizeError{Off: d.r.off, Op: "Int64Array", GoLength: val.Cap(), NBTLength: int(length)}
}
val.Set(value)
case tagSlice:
d.depth++
listType, err := d.r.ReadByte()
if err != nil {
return BufferOverrunError{Op: "List"}
}
if !tagExists(listType) {
return UnknownTagError{Off: d.r.off, TagType: listType, Op: "Slice"}
}
length, err := d.Encoding.Int32(d.r)
if err != nil {
return err
}
valType := val.Type()
if val.Kind() != reflect.Slice && val.Kind() != reflect.Interface {
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
if val.Kind() == reflect.Interface {
valType = reflect.SliceOf(valType)
}
v := reflect.MakeSlice(valType, int(length), int(length))
if length != 0 {
for i := 0; i < int(length); i++ {
if err := d.unmarshalTag(v.Index(i), listType, ""); err != nil {
// An error occurred during the decoding of one of the elements of the TAG_List, meaning it
// either had an invalid type or the NBT was invalid.
if _, ok := err.(InvalidTypeError); ok {
return InvalidTypeError{Off: d.r.off, FieldType: valType.Elem(), Field: fmt.Sprintf("%v[%v]", tagName, i), TagType: listType}
}
return err
}
}
}
val.Set(v)
d.depth--
case tagStruct:
d.depth++
switch val.Kind() {
default:
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
case reflect.Struct:
// We first fetch a fields map from the sync.Pool. These maps already have a base size obtained
// from when they were used, meaning we don't have to re-allocate each element.
fields := fieldMapPool.Get().(map[string]reflect.Value)
d.populateFields(val, fields)
for {
nestedTagType, nestedTagName, err := d.tag()
if err != nil {
return err
}
if nestedTagType == tagEnd {
// We reached the end of the fields.
break
}
field, ok := fields[nestedTagName]
if ok {
err = d.unmarshalTag(field, nestedTagType, nestedTagName)
if err != nil {
return err
}
continue
}
// We return an error if the struct does not have one of the fields found in the compound. It
// is rather important no data is lost during the decoding.
return UnexpectedNamedTagError{Off: d.r.off, TagName: tagName + "." + nestedTagName, TagType: nestedTagType}
}
// Finally we delete all fields in the map and return it to the sync.Pool so that it may be
// re-used by the next operation.
for k := range fields {
delete(fields, k)
}
fieldMapPool.Put(fields)
case reflect.Interface, reflect.Map:
if vk := val.Kind(); vk == reflect.Interface && val.NumMethod() != 0 {
return InvalidTypeError{Off: d.r.off, FieldType: val.Type(), Field: tagName, TagType: tagType}
}
valType := val.Type()
if val.Kind() == reflect.Map {
valType = valType.Elem()
}
m := reflect.MakeMap(reflect.MapOf(stringType, valType))
for {
nestedTagType, nestedTagName, err := d.tag()
if err != nil {
return err
}
if nestedTagType == tagEnd {
// We reached the end of the compound.
break
}
value := reflect.New(valType).Elem()
if err := d.unmarshalTag(value, nestedTagType, nestedTagName); err != nil {
return err
}
m.SetMapIndex(reflect.ValueOf(nestedTagName), value)
}
val.Set(m)
}
d.depth--
}
return nil
}
// populateFields populates the map passed with the fields of the reflect representation of a struct passed.
// It takes into consideration the nbt struct field tag.
func (d *Decoder) populateFields(val reflect.Value, m map[string]reflect.Value) {
for i := 0; i < val.NumField(); i++ {
fieldType := val.Type().Field(i)
if !ast.IsExported(fieldType.Name) {
// The struct field's name was not exported.
continue
}
field := val.Field(i)
name := fieldType.Name
if fieldType.Anonymous {
// We got an anonymous struct field, so we decode that into the same level.
d.populateFields(field, m)
continue
}
if tag, ok := fieldType.Tag.Lookup("nbt"); ok {
if tag == "-" {
continue
}
tag = strings.TrimSuffix(tag, ",omitempty")
if tag != "" {
name = tag
}
}
m[name] = field
}
}
// tag reads a tag from the decoder, and its name if the tag type is not a TAG_End.
func (d *Decoder) tag() (tagType byte, tagName string, err error) {
if d.depth >= maximumNestingDepth {
return 0, "", MaximumDepthReachedError{}
}
if d.r.off >= maximumNetworkOffset && d.Encoding == NetworkLittleEndian {
return 0, "", MaximumBytesReadError{}
}
tagType, err = d.r.ReadByte()
if err != nil {
return 0, "", BufferOverrunError{Op: "ReadTag"}
}
if tagType != tagEnd {
// Only read a tag name if the tag's type is not TAG_End.
tagName, err = d.Encoding.String(d.r)
}
return
}