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framedec.go
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framedec.go
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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 (
"encoding/binary"
"encoding/hex"
"errors"
"io"
"github.com/klauspost/compress/zstd/internal/xxhash"
)
type frameDec struct {
o decoderOptions
crc *xxhash.Digest
WindowSize uint64
// Frame history passed between blocks
history history
rawInput byteBuffer
// Byte buffer that can be reused for small input blocks.
bBuf byteBuf
FrameContentSize uint64
DictionaryID uint32
HasCheckSum bool
SingleSegment bool
}
const (
// MinWindowSize is the minimum Window Size, which is 1 KB.
MinWindowSize = 1 << 10
// MaxWindowSize is the maximum encoder window size
// and the default decoder maximum window size.
MaxWindowSize = 1 << 29
)
const (
frameMagic = "\x28\xb5\x2f\xfd"
skippableFrameMagic = "\x2a\x4d\x18"
)
func newFrameDec(o decoderOptions) *frameDec {
if o.maxWindowSize > o.maxDecodedSize {
o.maxWindowSize = o.maxDecodedSize
}
d := frameDec{
o: o,
}
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 signature [4]byte
for {
var err error
// Check if we can read more...
b, err := br.readSmall(1)
switch err {
case io.EOF, io.ErrUnexpectedEOF:
return io.EOF
case nil:
signature[0] = b[0]
default:
return err
}
// Read the rest, don't allow io.ErrUnexpectedEOF
b, err = br.readSmall(3)
switch err {
case io.EOF:
return io.EOF
case nil:
copy(signature[1:], b)
default:
return err
}
if string(signature[1:4]) != skippableFrameMagic || signature[0]&0xf0 != 0x50 {
if debugDecoder {
println("Not skippable", hex.EncodeToString(signature[:]), hex.EncodeToString([]byte(skippableFrameMagic)))
}
// Break if not skippable frame.
break
}
// Read size to skip
b, err = br.readSmall(4)
if err != nil {
if debugDecoder {
println("Reading Frame Size", err)
}
return err
}
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(int64(n))
if err != nil {
if debugDecoder {
println("Reading discarded frame", err)
}
return err
}
}
if string(signature[:]) != frameMagic {
if debugDecoder {
println("Got magic numbers: ", signature, "want:", []byte(frameMagic))
}
return ErrMagicMismatch
}
// Read Frame_Header_Descriptor
fhd, err := br.readByte()
if err != nil {
if debugDecoder {
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 {
if debugDecoder {
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 = 0
if size := fhd & 3; size != 0 {
if size == 3 {
size = 4
}
b, err := br.readSmall(int(size))
if err != nil {
println("Reading Dictionary_ID", err)
return err
}
var id uint32
switch len(b) {
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 debugDecoder {
println("Dict size", size, "ID:", id)
}
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 = fcsUnknown
if fcsSize > 0 {
b, err := br.readSmall(fcsSize)
if err != nil {
println("Reading Frame content", err)
return err
}
switch len(b) {
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 debugDecoder {
println("Read FCS:", d.FrameContentSize)
}
}
// 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 > d.o.maxWindowSize {
if debugDecoder {
printf("window size %d > max %d\n", d.WindowSize, d.o.maxWindowSize)
}
return ErrWindowSizeExceeded
}
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.o.maxDecodedSize {
if debugDecoder {
printf("window size %d > max %d\n", d.WindowSize, d.o.maxWindowSize)
}
return ErrDecoderSizeExceeded
}
}
// The minimum Window_Size is 1 KB.
if d.WindowSize < MinWindowSize {
if debugDecoder {
println("got window size: ", d.WindowSize)
}
return ErrWindowSizeTooSmall
}
d.history.windowSize = int(d.WindowSize)
if !d.o.lowMem || d.history.windowSize < maxBlockSize {
// Alloc 2x window size if not low-mem, or window size below 2MB.
d.history.allocFrameBuffer = d.history.windowSize * 2
} else {
if d.o.lowMem {
// Alloc with 1MB extra.
d.history.allocFrameBuffer = d.history.windowSize + maxBlockSize/2
} else {
// Alloc with 2MB extra.
d.history.allocFrameBuffer = d.history.windowSize + maxBlockSize
}
}
if debugDecoder {
println("Frame: Dict:", d.DictionaryID, "FrameContentSize:", d.FrameContentSize, "singleseg:", d.SingleSegment, "window:", d.WindowSize, "crc:", d.HasCheckSum)
}
// 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 debugDecoder {
println("decoding new block")
}
err := block.reset(d.rawInput, d.WindowSize)
if err != nil {
println("block error:", err)
// Signal the frame decoder we have a problem.
block.sendErr(err)
return err
}
return nil
}
// checkCRC will check the checksum, assuming the frame has one.
// Will return ErrCRCMismatch if crc check failed, otherwise nil.
func (d *frameDec) checkCRC() error {
// We can overwrite upper tmp now
buf, err := d.rawInput.readSmall(4)
if err != nil {
println("CRC missing?", err)
return err
}
want := binary.LittleEndian.Uint32(buf[:4])
got := uint32(d.crc.Sum64())
if got != want {
if debugDecoder {
printf("CRC check failed: got %08x, want %08x\n", got, want)
}
return ErrCRCMismatch
}
if debugDecoder {
printf("CRC ok %08x\n", got)
}
return nil
}
// consumeCRC skips over the checksum, assuming the frame has one.
func (d *frameDec) consumeCRC() error {
_, err := d.rawInput.readSmall(4)
if err != nil {
println("CRC missing?", err)
}
return err
}
// runDecoder will run the decoder for the remainder of the frame.
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
d.history.ignoreBuffer = len(dst)
// Store input length, so we only check new data.
crcStart := len(dst)
d.history.decoders.maxSyncLen = 0
if d.o.limitToCap {
d.history.decoders.maxSyncLen = uint64(cap(dst) - len(dst))
}
if d.FrameContentSize != fcsUnknown {
if !d.o.limitToCap || d.FrameContentSize+uint64(len(dst)) < d.history.decoders.maxSyncLen {
d.history.decoders.maxSyncLen = d.FrameContentSize + uint64(len(dst))
}
if d.history.decoders.maxSyncLen > d.o.maxDecodedSize {
if debugDecoder {
println("maxSyncLen:", d.history.decoders.maxSyncLen, "> maxDecodedSize:", d.o.maxDecodedSize)
}
return dst, ErrDecoderSizeExceeded
}
if debugDecoder {
println("maxSyncLen:", d.history.decoders.maxSyncLen)
}
if !d.o.limitToCap && uint64(cap(dst)) < d.history.decoders.maxSyncLen {
// Alloc for output
dst2 := make([]byte, len(dst), d.history.decoders.maxSyncLen+compressedBlockOverAlloc)
copy(dst2, dst)
dst = dst2
}
}
var err error
for {
err = dec.reset(d.rawInput, d.WindowSize)
if err != nil {
break
}
if debugDecoder {
println("next block:", dec)
}
err = dec.decodeBuf(&d.history)
if err != nil {
break
}
if uint64(len(d.history.b)-crcStart) > d.o.maxDecodedSize {
println("runDecoder: maxDecodedSize exceeded", uint64(len(d.history.b)-crcStart), ">", d.o.maxDecodedSize)
err = ErrDecoderSizeExceeded
break
}
if d.o.limitToCap && len(d.history.b) > cap(dst) {
println("runDecoder: cap exceeded", uint64(len(d.history.b)), ">", cap(dst))
err = ErrDecoderSizeExceeded
break
}
if uint64(len(d.history.b)-crcStart) > d.FrameContentSize {
println("runDecoder: FrameContentSize exceeded", uint64(len(d.history.b)-crcStart), ">", d.FrameContentSize)
err = ErrFrameSizeExceeded
break
}
if dec.Last {
break
}
if debugDecoder {
println("runDecoder: FrameContentSize", uint64(len(d.history.b)-crcStart), "<=", d.FrameContentSize)
}
}
dst = d.history.b
if err == nil {
if d.FrameContentSize != fcsUnknown && uint64(len(d.history.b)-crcStart) != d.FrameContentSize {
err = ErrFrameSizeMismatch
} else if d.HasCheckSum {
if d.o.ignoreChecksum {
err = d.consumeCRC()
} else {
d.crc.Write(dst[crcStart:])
err = d.checkCRC()
}
}
}
d.history.b = saved
return dst, err
}