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// Package lz4stream provides the types that support reading and writing LZ4 data streams.
package lz4stream
import (
"encoding/binary"
"fmt"
"io"
"io/ioutil"
"github.com/pierrec/lz4/v4/internal/lz4block"
"github.com/pierrec/lz4/v4/internal/lz4errors"
"github.com/pierrec/lz4/v4/internal/xxh32"
)
//go:generate go run gen.go
const (
frameMagic uint32 = 0x184D2204
frameSkipMagic uint32 = 0x184D2A50
frameMagicLegacy uint32 = 0x184C2102
)
func NewFrame() *Frame {
return &Frame{}
}
type Frame struct {
buf [15]byte // frame descriptor needs at most 4(magic)+4+8+1=11 bytes
Magic uint32
Descriptor FrameDescriptor
Blocks Blocks
Checksum uint32
checksum xxh32.XXHZero
}
// Reset allows reusing the Frame.
// The Descriptor configuration is not modified.
func (f *Frame) Reset(num int) {
f.Magic = 0
f.Descriptor.Checksum = 0
f.Descriptor.ContentSize = 0
_ = f.Blocks.close(f, num)
f.Checksum = 0
}
func (f *Frame) InitW(dst io.Writer, num int, legacy bool) {
if legacy {
f.Magic = frameMagicLegacy
idx := lz4block.Index(lz4block.Block8Mb)
f.Descriptor.Flags.BlockSizeIndexSet(idx)
} else {
f.Magic = frameMagic
f.Descriptor.initW()
}
f.Blocks.initW(f, dst, num)
f.checksum.Reset()
}
func (f *Frame) CloseW(dst io.Writer, num int) error {
if err := f.Blocks.close(f, num); err != nil {
return err
}
if f.isLegacy() {
return nil
}
buf := f.buf[:0]
// End mark (data block size of uint32(0)).
buf = append(buf, 0, 0, 0, 0)
if f.Descriptor.Flags.ContentChecksum() {
buf = f.checksum.Sum(buf)
}
_, err := dst.Write(buf)
return err
}
func (f *Frame) isLegacy() bool {
return f.Magic == frameMagicLegacy
}
func (f *Frame) ParseHeaders(src io.Reader) error {
if f.Magic > 0 {
// Header already read.
return nil
}
newFrame:
var err error
if f.Magic, err = f.readUint32(src); err != nil {
return err
}
switch m := f.Magic; {
case m == frameMagic || m == frameMagicLegacy:
// All 16 values of frameSkipMagic are valid.
case m>>8 == frameSkipMagic>>8:
skip, err := f.readUint32(src)
if err != nil {
return err
}
if _, err := io.CopyN(ioutil.Discard, src, int64(skip)); err != nil {
return err
}
goto newFrame
default:
return lz4errors.ErrInvalidFrame
}
if err := f.Descriptor.initR(f, src); err != nil {
return err
}
f.checksum.Reset()
return nil
}
func (f *Frame) InitR(src io.Reader, num int) (chan []byte, error) {
return f.Blocks.initR(f, num, src)
}
func (f *Frame) CloseR(src io.Reader) (err error) {
if f.isLegacy() {
return nil
}
if !f.Descriptor.Flags.ContentChecksum() {
return nil
}
if f.Checksum, err = f.readUint32(src); err != nil {
return err
}
if c := f.checksum.Sum32(); c != f.Checksum {
return fmt.Errorf("%w: got %x; expected %x", lz4errors.ErrInvalidFrameChecksum, c, f.Checksum)
}
return nil
}
type FrameDescriptor struct {
Flags DescriptorFlags
ContentSize uint64
Checksum uint8
}
func (fd *FrameDescriptor) initW() {
fd.Flags.VersionSet(1)
fd.Flags.BlockIndependenceSet(true)
}
func (fd *FrameDescriptor) Write(f *Frame, dst io.Writer) error {
if fd.Checksum > 0 {
// Header already written.
return nil
}
buf := f.buf[:4]
// Write the magic number here even though it belongs to the Frame.
binary.LittleEndian.PutUint32(buf, f.Magic)
if !f.isLegacy() {
buf = buf[:4+2]
binary.LittleEndian.PutUint16(buf[4:], uint16(fd.Flags))
if fd.Flags.Size() {
buf = buf[:4+2+8]
binary.LittleEndian.PutUint64(buf[4+2:], fd.ContentSize)
}
fd.Checksum = descriptorChecksum(buf[4:])
buf = append(buf, fd.Checksum)
}
_, err := dst.Write(buf)
return err
}
func (fd *FrameDescriptor) initR(f *Frame, src io.Reader) error {
if f.isLegacy() {
idx := lz4block.Index(lz4block.Block8Mb)
f.Descriptor.Flags.BlockSizeIndexSet(idx)
return nil
}
// Read the flags and the checksum, hoping that there is not content size.
buf := f.buf[:3]
if _, err := io.ReadFull(src, buf); err != nil {
return err
}
descr := binary.LittleEndian.Uint16(buf)
fd.Flags = DescriptorFlags(descr)
if fd.Flags.Size() {
// Append the 8 missing bytes.
buf = buf[:3+8]
if _, err := io.ReadFull(src, buf[3:]); err != nil {
return err
}
fd.ContentSize = binary.LittleEndian.Uint64(buf[2:])
}
fd.Checksum = buf[len(buf)-1] // the checksum is the last byte
buf = buf[:len(buf)-1] // all descriptor fields except checksum
if c := descriptorChecksum(buf); fd.Checksum != c {
return fmt.Errorf("%w: got %x; expected %x", lz4errors.ErrInvalidHeaderChecksum, c, fd.Checksum)
}
// Validate the elements that can be.
if idx := fd.Flags.BlockSizeIndex(); !idx.IsValid() {
return lz4errors.ErrOptionInvalidBlockSize
}
return nil
}
func descriptorChecksum(buf []byte) byte {
return byte(xxh32.ChecksumZero(buf) >> 8)
}
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