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decode.go
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decode.go
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/*
Copyright 2020 Takahiro Yamashita
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package bit
import (
"encoding/binary"
"errors"
"fmt"
"github.com/goccy/go-reflect"
"io"
)
var errCannotInterface = errors.New("CanInterface returns false")
// Size returns size of v in bits.
/*
func Size(v interface{}) int {
val := reflect.ValueOf(v)
var i int = 0
sizeOfValueInBits(&i, val, false)
return i
}
*/
// This function will be panic if v doesn't support Bits function.
// if structtag is true, the function respects struct tag.
func sizeOfValueInBits(c *int, v reflect.Value, structtag bool) {
switch v.Kind() {
case reflect.Struct:
if structtag {
for i := 0; i < v.Type().NumField(); i++ {
if !v.Field(i).CanInterface() {
continue
}
f := v.Type().Field(i)
cnf := parseStructTag(f.Tag)
if cnf != nil && cnf.ignore {
continue
}
sizeOfValueInBits(c, v.Field(i), structtag)
}
} else {
for i := 0; i < v.NumField(); i++ {
if v.Field(i).CanInterface() {
sizeOfValueInBits(c, v.Field(i), structtag)
}
}
}
case reflect.Array, reflect.Slice:
if v.Len() == 0 {
return
}
var elemSize int
sizeOfValueInBits(&elemSize, v.Index(0), structtag)
*c += (elemSize * v.Len())
case reflect.Bool:
*c += 1
default:
/* int, uint, float familiy */
*c += v.Type().Bits()
}
}
// read reads from b and fill v.
func read(b []byte, order binary.ByteOrder, v reflect.Value, o *Offset) error {
var off Offset
var err error
var val reflect.Value
if !v.CanInterface() {
// skip unexported field
var size int
sizeOfValueInBits(&size, v, false)
*o, err = o.AddOffset(Offset{Bit: uint64(size)})
if err != nil {
return err
}
return errCannotInterface
}
d := v.Interface()
switch d.(type) {
case uint8:
ret, err := GetBitsAsByte(b, *o, 8, binary.LittleEndian)
if err != nil {
return err
}
val = reflect.ValueOf(ret[0])
off = Offset{1, 0}
case uint16:
ret, err := GetBitsAsByte(b, *o, 16, binary.LittleEndian)
if err != nil {
return err
}
val = reflect.ValueOf(order.Uint16(ret))
off = Offset{2, 0}
case uint32:
ret, err := GetBitsAsByte(b, *o, 32, binary.LittleEndian)
if err != nil {
return err
}
val = reflect.ValueOf(order.Uint32(ret))
off = Offset{4, 0}
case uint64:
ret, err := GetBitsAsByte(b, *o, 64, binary.LittleEndian)
if err != nil {
return err
}
val = reflect.ValueOf(order.Uint64(ret))
off = Offset{8, 0}
case Bit:
ret, err := GetBitsBitEndian(b, *o, 1, order)
if err != nil {
return err
}
if ret[0] {
val = reflect.ValueOf(Bit(true))
} else {
val = reflect.ValueOf(Bit(false))
}
off = Offset{0, 1}
default: /* other data types */
switch v.Kind() {
case reflect.Array:
if v.Len() > 0 {
if v.Index(0).Kind() == reflect.Bool {
/* Bit array */
/* when order is Big Endian, we should read the entire bits at once */
ret, err := GetBitsBitEndian(b, *o, uint64(v.Len()), order)
if err != nil {
return err
}
// set data
for i := 0; i < v.Len(); i++ {
if v.Index(i).CanSet() {
v.Index(i).Set(reflect.ValueOf(Bit(ret[i])))
}
}
*o, err = o.AddOffset(Offset{Bit: uint64(v.Len())})
if err != nil {
return err
}
return nil
} else if v.Index(0).Kind() == reflect.Uint8 {
ret, err := GetBitsAsByte(b, *o, uint64(v.Len()*8), binary.LittleEndian)
if err != nil {
return err
}
for i := 0; i < v.Len(); i++ {
if v.Index(i).CanSet() {
if order == binary.BigEndian {
// workaround! binary.Read doesn't support []byte in BigEndian
v.Index(i).Set(reflect.ValueOf(ret[v.Len()-1-i]))
} else {
v.Index(i).Set(reflect.ValueOf(ret[i]))
}
}
}
*o, err = o.AddOffset(Offset{Byte: uint64(v.Len())})
if err != nil {
return err
}
return nil
} else {
for i := 0; i < v.Len(); i++ {
err := read(b, order, v.Index(i), o)
if err != nil && err != errCannotInterface {
return err
}
}
return nil
}
}
case reflect.Struct:
for i := 0; i < v.Type().NumField(); i++ {
f := v.Type().Field(i)
cnf := parseStructTag(f.Tag)
if cnf != nil {
/* struct tag is defined */
if cnf.ignore {
continue
} else if cnf.skip {
var bitSize int
/* only updates offset. not fill. */
sizeOfValueInBits(&bitSize, v.Field(i), true)
*o, err = o.AddOffset(Offset{Bit: uint64(bitSize)})
if err != nil {
return err
}
continue
} else if cnf.endian != nil {
err := read(b, cnf.endian, v.Field(i), o)
if err != nil && err != errCannotInterface {
return err
}
continue
}
}
err := read(b, order, v.Field(i), o)
if err != nil && err != errCannotInterface {
return err
}
}
return nil
default:
return fmt.Errorf("Not Supported %s", v.Kind())
}
}
// primitives
if v.CanSet() {
v.Set(val)
} else {
return fmt.Errorf("can not set %v\n", v)
}
*o, err = o.AddOffset(off)
if err != nil {
return err
}
return nil
}
// Read reads structured binary data from i into data.
// Data must be a pointer to a fixed-size value.
// Not exported struct field is ignored.
// Supports StructTag.
// `bit:"skip"` : ignore the field. Skip X bits which is the size of the field. It is useful for reserved field.
// `bit:"-"` : ignore the field. Offset is not changed.
func Read(r io.Reader, order binary.ByteOrder, data interface{}) error {
v := reflect.ValueOf(data)
switch v.Kind() {
case reflect.Ptr:
var c int = 0
sizeOfValueInBits(&c, reflect.Indirect(v), true)
byteSize := sizeOfBits(c)
barr := make([]byte, byteSize)
n, err := r.Read(barr)
if err != nil {
return err
} else if n != byteSize {
return fmt.Errorf("bit.Read:short read, expect=%d byte, read=%d byte", byteSize, n)
}
err = read(barr, order, reflect.Indirect(v), &Offset{})
if err != io.EOF && err != errCannotInterface {
return err
}
default:
return binary.Read(r, order, data)
}
return nil
}