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encoding.go
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encoding.go
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package nbt
import (
"errors"
"math"
"unsafe"
)
// Encoding is an encoding variant of NBT. In general, there are three different encodings of NBT, which are
// all the same except for the way basic types are written.
type Encoding interface {
Int16(r *offsetReader) (int16, error)
Int32(r *offsetReader) (int32, error)
Int64(r *offsetReader) (int64, error)
Float32(r *offsetReader) (float32, error)
Float64(r *offsetReader) (float64, error)
String(r *offsetReader) (string, error)
Int32Slice(r *offsetReader) ([]int32, error)
Int64Slice(r *offsetReader) ([]int64, error)
WriteInt16(w *offsetWriter, x int16) error
WriteInt32(w *offsetWriter, x int32) error
WriteInt64(w *offsetWriter, x int64) error
WriteFloat32(w *offsetWriter, x float32) error
WriteFloat64(w *offsetWriter, x float64) error
WriteString(w *offsetWriter, x string) error
}
var (
// NetworkLittleEndian is the variable sized integer implementation of NBT. It is otherwise the same as the
// normal little endian NBT. The NetworkLittleEndian format limits the total bytes of NBT that may be read. If
// the limit is hit, the reading operation will fail immediately. NetworkLittleEndian is generally used for NBT
// sent over network in the Bedrock Edition protocol.
NetworkLittleEndian networkLittleEndian
// LittleEndian is the fixed size little endian implementation of NBT. It is the format typically used for
// writing Minecraft (Bedrock Edition) world saves.
LittleEndian littleEndian
// BigEndian is the fixed size big endian implementation of NBT. It is the original implementation, and is
// used only on Minecraft Java Edition.
BigEndian bigEndian
_ Encoding = NetworkLittleEndian
_ Encoding = LittleEndian
_ Encoding = BigEndian
)
type networkLittleEndian struct{ littleEndian }
// WriteInt32 ...
func (networkLittleEndian) WriteInt32(w *offsetWriter, x int32) error {
ux := uint32(x) << 1
if x < 0 {
ux = ^ux
}
for ux >= 0x80 {
if err := w.WriteByte(byte(ux) | 0x80); err != nil {
return FailedWriteError{Op: "WriteInt32", Off: w.off}
}
ux >>= 7
}
if err := w.WriteByte(byte(ux)); err != nil {
return FailedWriteError{Op: "WriteInt32", Off: w.off}
}
return nil
}
// WriteInt64 ...
func (networkLittleEndian) WriteInt64(w *offsetWriter, x int64) error {
ux := uint64(x) << 1
if x < 0 {
ux = ^ux
}
for ux >= 0x80 {
if err := w.WriteByte(byte(ux) | 0x80); err != nil {
return FailedWriteError{Op: "WriteInt64", Off: w.off}
}
ux >>= 7
}
if err := w.WriteByte(byte(ux)); err != nil {
return FailedWriteError{Op: "WriteInt64", Off: w.off}
}
return nil
}
// WriteString ...
func (networkLittleEndian) WriteString(w *offsetWriter, x string) error {
if len(x) > math.MaxInt16 {
return InvalidStringError{Off: w.off, String: x, Err: errors.New("string length exceeds maximum length prefix")}
}
ux := uint32(len(x))
for ux >= 0x80 {
if err := w.WriteByte(byte(ux) | 0x80); err != nil {
return FailedWriteError{Op: "WriteString", Off: w.off}
}
ux >>= 7
}
if err := w.WriteByte(byte(ux)); err != nil {
return FailedWriteError{Op: "WriteString", Off: w.off}
}
// Use unsafe conversion from a string to a byte slice to prevent copying.
if _, err := w.Write(*(*[]byte)(unsafe.Pointer(&x))); err != nil {
return FailedWriteError{Op: "WriteString", Off: w.off}
}
return nil
}
// Int32 ...
func (networkLittleEndian) Int32(r *offsetReader) (int32, error) {
var ux uint32
for i := uint(0); i < 35; i += 7 {
b, err := r.ReadByte()
if err != nil {
return 0, BufferOverrunError{Op: "Int32"}
}
ux |= uint32(b&0x7f) << i
if b&0x80 == 0 {
break
}
}
x := int32(ux >> 1)
if ux&1 != 0 {
x = ^x
}
return x, nil
}
// Int64 ...
func (networkLittleEndian) Int64(r *offsetReader) (int64, error) {
var ux uint64
for i := uint(0); i < 70; i += 7 {
b, err := r.ReadByte()
if err != nil {
return 0, BufferOverrunError{Op: "Int64"}
}
ux |= uint64(b&0x7f) << i
if b&0x80 == 0 {
break
}
}
x := int64(ux >> 1)
if ux&1 != 0 {
x = ^x
}
return x, nil
}
// String ...
func (e networkLittleEndian) String(r *offsetReader) (string, error) {
var length uint32
for i := uint(0); i < 35; i += 7 {
b, err := r.ReadByte()
if err != nil {
return "", BufferOverrunError{Op: "String"}
}
length |= uint32(b&0x7f) << i
if b&0x80 == 0 {
break
}
}
if length > math.MaxInt16 {
return "", InvalidStringError{Off: r.off, Err: errors.New("string length exceeds maximum length prefix")}
}
data := make([]byte, length)
if _, err := r.Read(data); err != nil {
return "", BufferOverrunError{Op: "String"}
}
return *(*string)(unsafe.Pointer(&data)), nil
}
// Int32Slice ...
func (e networkLittleEndian) Int32Slice(r *offsetReader) ([]int32, error) {
n, err := e.Int32(r)
if err != nil {
return nil, BufferOverrunError{Op: "Int32Slice"}
}
m := make([]int32, n)
for i := int32(0); i < n; i++ {
m[i], err = e.Int32(r)
if err != nil {
return nil, BufferOverrunError{Op: "Int32Slice"}
}
}
return m, nil
}
// Int64Slice ...
func (e networkLittleEndian) Int64Slice(r *offsetReader) ([]int64, error) {
n, err := e.Int32(r)
if err != nil {
return nil, BufferOverrunError{Op: "Int64Slice"}
}
m := make([]int64, n)
for i := int32(0); i < n; i++ {
m[i], err = e.Int64(r)
if err != nil {
return nil, BufferOverrunError{Op: "Int64Slice"}
}
}
return m, nil
}