416 lines
10 KiB
Go
416 lines
10 KiB
Go
// Copyright 2019+ Klaus Post. All rights reserved.
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// License information can be found in the LICENSE file.
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// Based on work by Yann Collet, released under BSD License.
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package zstd
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import (
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"encoding/binary"
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"encoding/hex"
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"errors"
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"io"
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"github.com/klauspost/compress/zstd/internal/xxhash"
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)
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type frameDec struct {
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o decoderOptions
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crc *xxhash.Digest
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WindowSize uint64
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// Frame history passed between blocks
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history history
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rawInput byteBuffer
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// Byte buffer that can be reused for small input blocks.
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bBuf byteBuf
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FrameContentSize uint64
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DictionaryID uint32
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HasCheckSum bool
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SingleSegment bool
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}
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const (
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// MinWindowSize is the minimum Window Size, which is 1 KB.
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MinWindowSize = 1 << 10
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// MaxWindowSize is the maximum encoder window size
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// and the default decoder maximum window size.
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MaxWindowSize = 1 << 29
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)
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const (
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frameMagic = "\x28\xb5\x2f\xfd"
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skippableFrameMagic = "\x2a\x4d\x18"
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)
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func newFrameDec(o decoderOptions) *frameDec {
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if o.maxWindowSize > o.maxDecodedSize {
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o.maxWindowSize = o.maxDecodedSize
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}
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d := frameDec{
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o: o,
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}
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return &d
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}
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// reset will read the frame header and prepare for block decoding.
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// If nothing can be read from the input, io.EOF will be returned.
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// Any other error indicated that the stream contained data, but
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// there was a problem.
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func (d *frameDec) reset(br byteBuffer) error {
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d.HasCheckSum = false
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d.WindowSize = 0
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var signature [4]byte
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for {
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var err error
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// Check if we can read more...
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b, err := br.readSmall(1)
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switch err {
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case io.EOF, io.ErrUnexpectedEOF:
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return io.EOF
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case nil:
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signature[0] = b[0]
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default:
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return err
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}
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// Read the rest, don't allow io.ErrUnexpectedEOF
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b, err = br.readSmall(3)
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switch err {
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case io.EOF:
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return io.EOF
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case nil:
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copy(signature[1:], b)
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default:
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return err
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}
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if string(signature[1:4]) != skippableFrameMagic || signature[0]&0xf0 != 0x50 {
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if debugDecoder {
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println("Not skippable", hex.EncodeToString(signature[:]), hex.EncodeToString([]byte(skippableFrameMagic)))
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}
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// Break if not skippable frame.
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break
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}
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// Read size to skip
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b, err = br.readSmall(4)
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if err != nil {
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if debugDecoder {
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println("Reading Frame Size", err)
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}
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return err
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}
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n := uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
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println("Skipping frame with", n, "bytes.")
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err = br.skipN(int64(n))
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if err != nil {
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if debugDecoder {
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println("Reading discarded frame", err)
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}
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return err
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}
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}
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if string(signature[:]) != frameMagic {
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if debugDecoder {
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println("Got magic numbers: ", signature, "want:", []byte(frameMagic))
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}
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return ErrMagicMismatch
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}
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// Read Frame_Header_Descriptor
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fhd, err := br.readByte()
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if err != nil {
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if debugDecoder {
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println("Reading Frame_Header_Descriptor", err)
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}
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return err
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}
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d.SingleSegment = fhd&(1<<5) != 0
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if fhd&(1<<3) != 0 {
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return errors.New("reserved bit set on frame header")
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}
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// Read Window_Descriptor
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// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#window_descriptor
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d.WindowSize = 0
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if !d.SingleSegment {
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wd, err := br.readByte()
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if err != nil {
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if debugDecoder {
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println("Reading Window_Descriptor", err)
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}
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return err
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}
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if debugDecoder {
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printf("raw: %x, mantissa: %d, exponent: %d\n", wd, wd&7, wd>>3)
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}
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windowLog := 10 + (wd >> 3)
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windowBase := uint64(1) << windowLog
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windowAdd := (windowBase / 8) * uint64(wd&0x7)
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d.WindowSize = windowBase + windowAdd
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}
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// Read Dictionary_ID
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// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#dictionary_id
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d.DictionaryID = 0
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if size := fhd & 3; size != 0 {
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if size == 3 {
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size = 4
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}
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b, err := br.readSmall(int(size))
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if err != nil {
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println("Reading Dictionary_ID", err)
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return err
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}
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var id uint32
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switch len(b) {
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case 1:
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id = uint32(b[0])
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case 2:
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id = uint32(b[0]) | (uint32(b[1]) << 8)
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case 4:
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id = uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
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}
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if debugDecoder {
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println("Dict size", size, "ID:", id)
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}
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d.DictionaryID = id
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}
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// Read Frame_Content_Size
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// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#frame_content_size
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var fcsSize int
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v := fhd >> 6
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switch v {
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case 0:
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if d.SingleSegment {
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fcsSize = 1
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}
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default:
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fcsSize = 1 << v
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}
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d.FrameContentSize = fcsUnknown
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if fcsSize > 0 {
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b, err := br.readSmall(fcsSize)
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if err != nil {
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println("Reading Frame content", err)
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return err
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}
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switch len(b) {
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case 1:
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d.FrameContentSize = uint64(b[0])
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case 2:
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// When FCS_Field_Size is 2, the offset of 256 is added.
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d.FrameContentSize = uint64(b[0]) | (uint64(b[1]) << 8) + 256
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case 4:
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d.FrameContentSize = uint64(b[0]) | (uint64(b[1]) << 8) | (uint64(b[2]) << 16) | (uint64(b[3]) << 24)
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case 8:
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d1 := uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
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d2 := uint32(b[4]) | (uint32(b[5]) << 8) | (uint32(b[6]) << 16) | (uint32(b[7]) << 24)
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d.FrameContentSize = uint64(d1) | (uint64(d2) << 32)
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}
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if debugDecoder {
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println("Read FCS:", d.FrameContentSize)
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}
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}
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// Move this to shared.
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d.HasCheckSum = fhd&(1<<2) != 0
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if d.HasCheckSum {
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if d.crc == nil {
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d.crc = xxhash.New()
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}
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d.crc.Reset()
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}
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if d.WindowSize > d.o.maxWindowSize {
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if debugDecoder {
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printf("window size %d > max %d\n", d.WindowSize, d.o.maxWindowSize)
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}
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return ErrWindowSizeExceeded
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}
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if d.WindowSize == 0 && d.SingleSegment {
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// We may not need window in this case.
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d.WindowSize = d.FrameContentSize
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if d.WindowSize < MinWindowSize {
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d.WindowSize = MinWindowSize
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}
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if d.WindowSize > d.o.maxDecodedSize {
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if debugDecoder {
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printf("window size %d > max %d\n", d.WindowSize, d.o.maxWindowSize)
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}
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return ErrDecoderSizeExceeded
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}
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}
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// The minimum Window_Size is 1 KB.
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if d.WindowSize < MinWindowSize {
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if debugDecoder {
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println("got window size: ", d.WindowSize)
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}
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return ErrWindowSizeTooSmall
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}
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d.history.windowSize = int(d.WindowSize)
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if !d.o.lowMem || d.history.windowSize < maxBlockSize {
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// Alloc 2x window size if not low-mem, or window size below 2MB.
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d.history.allocFrameBuffer = d.history.windowSize * 2
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} else {
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if d.o.lowMem {
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// Alloc with 1MB extra.
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d.history.allocFrameBuffer = d.history.windowSize + maxBlockSize/2
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} else {
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// Alloc with 2MB extra.
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d.history.allocFrameBuffer = d.history.windowSize + maxBlockSize
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}
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}
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if debugDecoder {
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println("Frame: Dict:", d.DictionaryID, "FrameContentSize:", d.FrameContentSize, "singleseg:", d.SingleSegment, "window:", d.WindowSize, "crc:", d.HasCheckSum)
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}
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// history contains input - maybe we do something
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d.rawInput = br
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return nil
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}
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// next will start decoding the next block from stream.
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func (d *frameDec) next(block *blockDec) error {
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if debugDecoder {
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println("decoding new block")
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}
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err := block.reset(d.rawInput, d.WindowSize)
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if err != nil {
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println("block error:", err)
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// Signal the frame decoder we have a problem.
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block.sendErr(err)
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return err
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}
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return nil
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}
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// checkCRC will check the checksum, assuming the frame has one.
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// Will return ErrCRCMismatch if crc check failed, otherwise nil.
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func (d *frameDec) checkCRC() error {
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// We can overwrite upper tmp now
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buf, err := d.rawInput.readSmall(4)
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if err != nil {
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println("CRC missing?", err)
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return err
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}
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want := binary.LittleEndian.Uint32(buf[:4])
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got := uint32(d.crc.Sum64())
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if got != want {
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if debugDecoder {
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printf("CRC check failed: got %08x, want %08x\n", got, want)
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}
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return ErrCRCMismatch
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}
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if debugDecoder {
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printf("CRC ok %08x\n", got)
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}
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return nil
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}
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// consumeCRC skips over the checksum, assuming the frame has one.
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func (d *frameDec) consumeCRC() error {
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_, err := d.rawInput.readSmall(4)
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if err != nil {
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println("CRC missing?", err)
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}
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return err
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}
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// runDecoder will run the decoder for the remainder of the frame.
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func (d *frameDec) runDecoder(dst []byte, dec *blockDec) ([]byte, error) {
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saved := d.history.b
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// We use the history for output to avoid copying it.
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d.history.b = dst
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d.history.ignoreBuffer = len(dst)
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// Store input length, so we only check new data.
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crcStart := len(dst)
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d.history.decoders.maxSyncLen = 0
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if d.o.limitToCap {
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d.history.decoders.maxSyncLen = uint64(cap(dst) - len(dst))
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}
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if d.FrameContentSize != fcsUnknown {
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if !d.o.limitToCap || d.FrameContentSize+uint64(len(dst)) < d.history.decoders.maxSyncLen {
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d.history.decoders.maxSyncLen = d.FrameContentSize + uint64(len(dst))
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}
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if d.history.decoders.maxSyncLen > d.o.maxDecodedSize {
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if debugDecoder {
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println("maxSyncLen:", d.history.decoders.maxSyncLen, "> maxDecodedSize:", d.o.maxDecodedSize)
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}
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return dst, ErrDecoderSizeExceeded
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}
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if debugDecoder {
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println("maxSyncLen:", d.history.decoders.maxSyncLen)
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}
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if !d.o.limitToCap && uint64(cap(dst)) < d.history.decoders.maxSyncLen {
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// Alloc for output
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dst2 := make([]byte, len(dst), d.history.decoders.maxSyncLen+compressedBlockOverAlloc)
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copy(dst2, dst)
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dst = dst2
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}
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}
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var err error
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for {
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err = dec.reset(d.rawInput, d.WindowSize)
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if err != nil {
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break
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}
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if debugDecoder {
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println("next block:", dec)
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}
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err = dec.decodeBuf(&d.history)
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if err != nil {
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break
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}
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if uint64(len(d.history.b)-crcStart) > d.o.maxDecodedSize {
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println("runDecoder: maxDecodedSize exceeded", uint64(len(d.history.b)-crcStart), ">", d.o.maxDecodedSize)
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err = ErrDecoderSizeExceeded
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break
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}
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if d.o.limitToCap && len(d.history.b) > cap(dst) {
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println("runDecoder: cap exceeded", uint64(len(d.history.b)), ">", cap(dst))
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err = ErrDecoderSizeExceeded
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break
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}
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if uint64(len(d.history.b)-crcStart) > d.FrameContentSize {
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println("runDecoder: FrameContentSize exceeded", uint64(len(d.history.b)-crcStart), ">", d.FrameContentSize)
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err = ErrFrameSizeExceeded
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break
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}
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if dec.Last {
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break
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}
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if debugDecoder {
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println("runDecoder: FrameContentSize", uint64(len(d.history.b)-crcStart), "<=", d.FrameContentSize)
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}
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}
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dst = d.history.b
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if err == nil {
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if d.FrameContentSize != fcsUnknown && uint64(len(d.history.b)-crcStart) != d.FrameContentSize {
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err = ErrFrameSizeMismatch
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} else if d.HasCheckSum {
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if d.o.ignoreChecksum {
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err = d.consumeCRC()
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} else {
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d.crc.Write(dst[crcStart:])
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err = d.checkCRC()
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}
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}
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}
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d.history.b = saved
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return dst, err
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}
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