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// Copyright 2019+ Klaus Post. All rights reserved.
// License information can be found in the LICENSE file.
// Based on work by Yann Collet, released under BSD License.
package zstd
import (
"bytes"
"encoding/hex"
"errors"
"hash"
"io"
"sync"
"github.com/cespare/xxhash"
)
type frameDec struct {
o decoderOptions
crc hash.Hash64
offset int64
WindowSize uint64
// maxWindowSize is the maximum windows size to support.
// should never be bigger than max-int.
maxWindowSize uint64
// In order queue of blocks being decoded.
decoding chan *blockDec
// Frame history passed between blocks
history history
rawInput byteBuffer
// Byte buffer that can be reused for small input blocks.
bBuf byteBuf
FrameContentSize uint64
frameDone sync.WaitGroup
DictionaryID *uint32
HasCheckSum bool
SingleSegment bool
// asyncRunning indicates whether the async routine processes input on 'decoding'.
asyncRunningMu sync.Mutex
asyncRunning bool
}
const (
// The minimum Window_Size is 1 KB.
MinWindowSize = 1 << 10
MaxWindowSize = 1 << 29
)
var (
frameMagic = []byte{0x28, 0xb5, 0x2f, 0xfd}
skippableFrameMagic = []byte{0x2a, 0x4d, 0x18}
)
func newFrameDec(o decoderOptions) *frameDec {
d := frameDec{
o: o,
maxWindowSize: MaxWindowSize,
}
if d.maxWindowSize > o.maxDecodedSize {
d.maxWindowSize = o.maxDecodedSize
}
return &d
}
// reset will read the frame header and prepare for block decoding.
// If nothing can be read from the input, io.EOF will be returned.
// Any other error indicated that the stream contained data, but
// there was a problem.
func (d *frameDec) reset(br byteBuffer) error {
d.HasCheckSum = false
d.WindowSize = 0
var b []byte
for {
b = br.readSmall(4)
if b == nil {
return io.EOF
}
if !bytes.Equal(b[1:4], skippableFrameMagic) || b[0]&0xf0 != 0x50 {
if debug {
println("Not skippable", hex.EncodeToString(b), hex.EncodeToString(skippableFrameMagic))
}
// Break if not skippable frame.
break
}
// Read size to skip
b = br.readSmall(4)
if b == nil {
println("Reading Frame Size EOF")
return io.ErrUnexpectedEOF
}
n := uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
println("Skipping frame with", n, "bytes.")
err := br.skipN(int(n))
if err != nil {
if debug {
println("Reading discarded frame", err)
}
return err
}
}
if !bytes.Equal(b, frameMagic) {
println("Got magic numbers: ", b, "want:", frameMagic)
return ErrMagicMismatch
}
// Read Frame_Header_Descriptor
fhd, err := br.readByte()
if err != nil {
println("Reading Frame_Header_Descriptor", err)
return err
}
d.SingleSegment = fhd&(1<<5) != 0
if fhd&(1<<3) != 0 {
return errors.New("Reserved bit set on frame header")
}
// Read Window_Descriptor
// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#window_descriptor
d.WindowSize = 0
if !d.SingleSegment {
wd, err := br.readByte()
if err != nil {
println("Reading Window_Descriptor", err)
return err
}
printf("raw: %x, mantissa: %d, exponent: %d\n", wd, wd&7, wd>>3)
windowLog := 10 + (wd >> 3)
windowBase := uint64(1) << windowLog
windowAdd := (windowBase / 8) * uint64(wd&0x7)
d.WindowSize = windowBase + windowAdd
}
// Read Dictionary_ID
// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#dictionary_id
d.DictionaryID = nil
if size := fhd & 3; size != 0 {
if size == 3 {
size = 4
}
b = br.readSmall(int(size))
if b == nil {
if debug {
println("Reading Dictionary_ID", io.ErrUnexpectedEOF)
}
return io.ErrUnexpectedEOF
}
var id uint32
switch size {
case 1:
id = uint32(b[0])
case 2:
id = uint32(b[0]) | (uint32(b[1]) << 8)
case 4:
id = uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
}
if debug {
println("Dict size", size, "ID:", id)
}
if id > 0 {
// ID 0 means "sorry, no dictionary anyway".
// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#dictionary-format
d.DictionaryID = &id
}
}
// Read Frame_Content_Size
// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#frame_content_size
var fcsSize int
v := fhd >> 6
switch v {
case 0:
if d.SingleSegment {
fcsSize = 1
}
default:
fcsSize = 1 << v
}
d.FrameContentSize = 0
if fcsSize > 0 {
b := br.readSmall(fcsSize)
if b == nil {
println("Reading Frame content", io.ErrUnexpectedEOF)
return io.ErrUnexpectedEOF
}
switch fcsSize {
case 1:
d.FrameContentSize = uint64(b[0])
case 2:
// When FCS_Field_Size is 2, the offset of 256 is added.
d.FrameContentSize = uint64(b[0]) | (uint64(b[1]) << 8) + 256
case 4:
d.FrameContentSize = uint64(b[0]) | (uint64(b[1]) << 8) | (uint64(b[2]) << 16) | (uint64(b[3]) << 24)
case 8:
d1 := uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
d2 := uint32(b[4]) | (uint32(b[5]) << 8) | (uint32(b[6]) << 16) | (uint32(b[7]) << 24)
d.FrameContentSize = uint64(d1) | (uint64(d2) << 32)
}
if debug {
println("field size bits:", v, "fcsSize:", fcsSize, "FrameContentSize:", d.FrameContentSize, hex.EncodeToString(b[:fcsSize]), "singleseg:", d.SingleSegment, "window:", d.WindowSize)
}
}
// Move this to shared.
d.HasCheckSum = fhd&(1<<2) != 0
if d.HasCheckSum {
if d.crc == nil {
d.crc = xxhash.New()
}
d.crc.Reset()
}
if d.WindowSize == 0 && d.SingleSegment {
// We may not need window in this case.
d.WindowSize = d.FrameContentSize
if d.WindowSize < MinWindowSize {
d.WindowSize = MinWindowSize
}
}
if d.WindowSize > d.maxWindowSize {
printf("window size %d > max %d\n", d.WindowSize, d.maxWindowSize)
return ErrWindowSizeExceeded
}
// The minimum Window_Size is 1 KB.
if d.WindowSize < MinWindowSize {
println("got window size: ", d.WindowSize)
return ErrWindowSizeTooSmall
}
d.history.windowSize = int(d.WindowSize)
if d.o.lowMem && d.history.windowSize < maxBlockSize {
d.history.maxSize = d.history.windowSize * 2
} else {
d.history.maxSize = d.history.windowSize + maxBlockSize
}
// history contains input - maybe we do something
d.rawInput = br
return nil
}
// next will start decoding the next block from stream.
func (d *frameDec) next(block *blockDec) error {
if debug {
printf("decoding new block %p:%p", block, block.data)
}
err := block.reset(d.rawInput, d.WindowSize)
if err != nil {
println("block error:", err)
// Signal the frame decoder we have a problem.
d.sendErr(block, err)
return err
}
block.input <- struct{}{}
if debug {
println("next block:", block)
}
d.asyncRunningMu.Lock()
defer d.asyncRunningMu.Unlock()
if !d.asyncRunning {
return nil
}
if block.Last {
// We indicate the frame is done by sending io.EOF
d.decoding <- block
return io.EOF
}
d.decoding <- block
return nil
}
// sendEOF will queue an error block on the frame.
// This will cause the frame decoder to return when it encounters the block.
// Returns true if the decoder was added.
func (d *frameDec) sendErr(block *blockDec, err error) bool {
d.asyncRunningMu.Lock()
defer d.asyncRunningMu.Unlock()
if !d.asyncRunning {
return false
}
println("sending error", err.Error())
block.sendErr(err)
d.decoding <- block
return true
}
// checkCRC will check the checksum if the frame has one.
// Will return ErrCRCMismatch if crc check failed, otherwise nil.
func (d *frameDec) checkCRC() error {
if !d.HasCheckSum {
return nil
}
var tmp [4]byte
got := d.crc.Sum64()
// Flip to match file order.
tmp[0] = byte(got >> 0)
tmp[1] = byte(got >> 8)
tmp[2] = byte(got >> 16)
tmp[3] = byte(got >> 24)
// We can overwrite upper tmp now
want := d.rawInput.readSmall(4)
if want == nil {
println("CRC missing?")
return io.ErrUnexpectedEOF
}
if !bytes.Equal(tmp[:], want) {
if debug {
println("CRC Check Failed:", tmp[:], "!=", want)
}
return ErrCRCMismatch
}
if debug {
println("CRC ok", tmp[:])
}
return nil
}
func (d *frameDec) initAsync() {
if !d.o.lowMem && !d.SingleSegment {
// set max extra size history to 10MB.
d.history.maxSize = d.history.windowSize + maxBlockSize*5
}
// re-alloc if more than one extra block size.
if d.o.lowMem && cap(d.history.b) > d.history.maxSize+maxBlockSize {
d.history.b = make([]byte, 0, d.history.maxSize)
}
if cap(d.history.b) < d.history.maxSize {
d.history.b = make([]byte, 0, d.history.maxSize)
}
if cap(d.decoding) < d.o.concurrent {
d.decoding = make(chan *blockDec, d.o.concurrent)
}
if debug {
h := d.history
printf("history init. len: %d, cap: %d", len(h.b), cap(h.b))
}
d.asyncRunningMu.Lock()
d.asyncRunning = true
d.asyncRunningMu.Unlock()
}
// startDecoder will start decoding blocks and write them to the writer.
// The decoder will stop as soon as an error occurs or at end of frame.
// When the frame has finished decoding the *bufio.Reader
// containing the remaining input will be sent on frameDec.frameDone.
func (d *frameDec) startDecoder(output chan decodeOutput) {
written := int64(0)
defer func() {
d.asyncRunningMu.Lock()
d.asyncRunning = false
d.asyncRunningMu.Unlock()
// Drain the currently decoding.
d.history.error = true
flushdone:
for {
select {
case b := <-d.decoding:
b.history <- &d.history
output <- <-b.result
default:
break flushdone
}
}
println("frame decoder done, signalling done")
d.frameDone.Done()
}()
// Get decoder for first block.
block := <-d.decoding
block.history <- &d.history
for {
var next *blockDec
// Get result
r := <-block.result
if r.err != nil {
println("Result contained error", r.err)
output <- r
return
}
if debug {
println("got result, from ", d.offset, "to", d.offset+int64(len(r.b)))
d.offset += int64(len(r.b))
}
if !block.Last {
// Send history to next block
select {
case next = <-d.decoding:
if debug {
println("Sending ", len(d.history.b), "bytes as history")
}
next.history <- &d.history
default:
// Wait until we have sent the block, so
// other decoders can potentially get the decoder.
next = nil
}
}
// Add checksum, async to decoding.
if d.HasCheckSum {
n, err := d.crc.Write(r.b)
if err != nil {
r.err = err
if n != len(r.b) {
r.err = io.ErrShortWrite
}
output <- r
return
}
}
written += int64(len(r.b))
if d.SingleSegment && uint64(written) > d.FrameContentSize {
println("runDecoder: single segment and", uint64(written), ">", d.FrameContentSize)
r.err = ErrFrameSizeExceeded
output <- r
return
}
if block.Last {
r.err = d.checkCRC()
output <- r
return
}
output <- r
if next == nil {
// There was no decoder available, we wait for one now that we have sent to the writer.
if debug {
println("Sending ", len(d.history.b), " bytes as history")
}
next = <-d.decoding
next.history <- &d.history
}
block = next
}
}
// runDecoder will create a sync decoder that will decode a block of data.
func (d *frameDec) runDecoder(dst []byte, dec *blockDec) ([]byte, error) {
saved := d.history.b
// We use the history for output to avoid copying it.
d.history.b = dst
// Store input length, so we only check new data.
crcStart := len(dst)
var err error
for {
err = dec.reset(d.rawInput, d.WindowSize)
if err != nil {
break
}
if debug {
println("next block:", dec)
}
err = dec.decodeBuf(&d.history)
if err != nil || dec.Last {
break
}
if uint64(len(d.history.b)) > d.o.maxDecodedSize {
err = ErrDecoderSizeExceeded
break
}
if d.SingleSegment && uint64(len(d.history.b)) > d.o.maxDecodedSize {
println("runDecoder: single segment and", uint64(len(d.history.b)), ">", d.o.maxDecodedSize)
err = ErrFrameSizeExceeded
break
}
}
dst = d.history.b
if err == nil {
if d.HasCheckSum {
var n int
n, err = d.crc.Write(dst[crcStart:])
if err == nil {
if n != len(dst)-crcStart {
err = io.ErrShortWrite
} else {
err = d.checkCRC()
}
}
}
}
d.history.b = saved
return dst, err
}
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