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packing.go
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packing.go
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// Copyright (C) 2019-2023, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package wrappers
import (
"encoding/binary"
"errors"
"math"
)
const (
MaxStringLen = math.MaxUint16
// ByteLen is the number of bytes per byte...
ByteLen = 1
// ShortLen is the number of bytes per short
ShortLen = 2
// IntLen is the number of bytes per int
IntLen = 4
// LongLen is the number of bytes per long
LongLen = 8
// BoolLen is the number of bytes per bool
BoolLen = 1
// IPLen is the number of bytes per IP
IPLen = 16 + ShortLen
)
func StringLen(str string) int {
// note: there is a max length for string ([MaxStringLen])
// we defer to PackString checking whether str is within limits
return ShortLen + len(str)
}
var (
ErrInsufficientLength = errors.New("packer has insufficient length for input")
errNegativeOffset = errors.New("negative offset")
errInvalidInput = errors.New("input does not match expected format")
errBadBool = errors.New("unexpected value when unpacking bool")
errOversized = errors.New("size is larger than limit")
)
// Packer packs and unpacks a byte array from/to standard values
type Packer struct {
Errs
// The largest allowed size of expanding the byte array
MaxSize int
// The current byte array
Bytes []byte
// The offset that is being written to in the byte array
Offset int
}
// PackByte append a byte to the byte array
func (p *Packer) PackByte(val byte) {
p.expand(ByteLen)
if p.Errored() {
return
}
p.Bytes[p.Offset] = val
p.Offset++
}
// UnpackByte unpack a byte from the byte array
func (p *Packer) UnpackByte() byte {
p.checkSpace(ByteLen)
if p.Errored() {
return 0
}
val := p.Bytes[p.Offset]
p.Offset += ByteLen
return val
}
// PackShort append a short to the byte array
func (p *Packer) PackShort(val uint16) {
p.expand(ShortLen)
if p.Errored() {
return
}
binary.BigEndian.PutUint16(p.Bytes[p.Offset:], val)
p.Offset += ShortLen
}
// UnpackShort unpack a short from the byte array
func (p *Packer) UnpackShort() uint16 {
p.checkSpace(ShortLen)
if p.Errored() {
return 0
}
val := binary.BigEndian.Uint16(p.Bytes[p.Offset:])
p.Offset += ShortLen
return val
}
// PackInt append an int to the byte array
func (p *Packer) PackInt(val uint32) {
p.expand(IntLen)
if p.Errored() {
return
}
binary.BigEndian.PutUint32(p.Bytes[p.Offset:], val)
p.Offset += IntLen
}
// UnpackInt unpack an int from the byte array
func (p *Packer) UnpackInt() uint32 {
p.checkSpace(IntLen)
if p.Errored() {
return 0
}
val := binary.BigEndian.Uint32(p.Bytes[p.Offset:])
p.Offset += IntLen
return val
}
// PackLong append a long to the byte array
func (p *Packer) PackLong(val uint64) {
p.expand(LongLen)
if p.Errored() {
return
}
binary.BigEndian.PutUint64(p.Bytes[p.Offset:], val)
p.Offset += LongLen
}
// UnpackLong unpack a long from the byte array
func (p *Packer) UnpackLong() uint64 {
p.checkSpace(LongLen)
if p.Errored() {
return 0
}
val := binary.BigEndian.Uint64(p.Bytes[p.Offset:])
p.Offset += LongLen
return val
}
// PackBool packs a bool into the byte array
func (p *Packer) PackBool(b bool) {
if b {
p.PackByte(1)
} else {
p.PackByte(0)
}
}
// UnpackBool unpacks a bool from the byte array
func (p *Packer) UnpackBool() bool {
b := p.UnpackByte()
switch b {
case 0:
return false
case 1:
return true
default:
p.Add(errBadBool)
return false
}
}
// PackFixedBytes append a byte slice, with no length descriptor to the byte
// array
func (p *Packer) PackFixedBytes(bytes []byte) {
p.expand(len(bytes))
if p.Errored() {
return
}
copy(p.Bytes[p.Offset:], bytes)
p.Offset += len(bytes)
}
// UnpackFixedBytes unpack a byte slice, with no length descriptor from the byte
// array
func (p *Packer) UnpackFixedBytes(size int) []byte {
p.checkSpace(size)
if p.Errored() {
return nil
}
bytes := p.Bytes[p.Offset : p.Offset+size]
p.Offset += size
return bytes
}
// PackBytes append a byte slice to the byte array
func (p *Packer) PackBytes(bytes []byte) {
p.PackInt(uint32(len(bytes)))
p.PackFixedBytes(bytes)
}
// UnpackBytes unpack a byte slice from the byte array
func (p *Packer) UnpackBytes() []byte {
size := p.UnpackInt()
return p.UnpackFixedBytes(int(size))
}
// UnpackLimitedBytes unpacks a byte slice. If the size of the slice is greater
// than [limit], adds [errOversized] to the packer and returns nil.
func (p *Packer) UnpackLimitedBytes(limit uint32) []byte {
size := p.UnpackInt()
if size > limit {
p.Add(errOversized)
return nil
}
return p.UnpackFixedBytes(int(size))
}
// PackStr append a string to the byte array
func (p *Packer) PackStr(str string) {
strSize := len(str)
if strSize > MaxStringLen {
p.Add(errInvalidInput)
return
}
p.PackShort(uint16(strSize))
p.PackFixedBytes([]byte(str))
}
// UnpackStr unpacks a string from the byte array
func (p *Packer) UnpackStr() string {
strSize := p.UnpackShort()
return string(p.UnpackFixedBytes(int(strSize)))
}
// UnpackLimitedStr unpacks a string. If the size of the string is greater than
// [limit], adds [errOversized] to the packer and returns the empty string.
func (p *Packer) UnpackLimitedStr(limit uint16) string {
strSize := p.UnpackShort()
if strSize > limit {
p.Add(errOversized)
return ""
}
return string(p.UnpackFixedBytes(int(strSize)))
}
// checkSpace requires that there is at least [bytes] of write space left in the
// byte array. If this is not true, an error is added to the packer
func (p *Packer) checkSpace(bytes int) {
switch {
case p.Offset < 0:
p.Add(errNegativeOffset)
case bytes < 0:
p.Add(errInvalidInput)
case len(p.Bytes)-p.Offset < bytes:
p.Add(ErrInsufficientLength)
}
}
// expand ensures that there is [bytes] bytes left of space in the byte slice.
// If this is not allowed due to the maximum size, an error is added to the packer
// In order to understand this code, its important to understand the difference
// between a slice's length and its capacity.
func (p *Packer) expand(bytes int) {
neededSize := bytes + p.Offset // Need byte slice's length to be at least [neededSize]
switch {
case neededSize <= len(p.Bytes): // Byte slice has sufficient length already
return
case neededSize > p.MaxSize: // Lengthening the byte slice would cause it to grow too large
p.Err = ErrInsufficientLength
return
case neededSize <= cap(p.Bytes): // Byte slice has sufficient capacity to lengthen it without mem alloc
p.Bytes = p.Bytes[:neededSize]
return
default: // Add capacity/length to byte slice
p.Bytes = append(p.Bytes[:cap(p.Bytes)], make([]byte, neededSize-cap(p.Bytes))...)
}
}