522 lines
12 KiB
Go
522 lines
12 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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"bytes"
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"encoding/hex"
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"errors"
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"hash"
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"io"
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"sync"
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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 hash.Hash64
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offset int64
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WindowSize uint64
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// In order queue of blocks being decoded.
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decoding chan *blockDec
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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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frameDone sync.WaitGroup
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DictionaryID *uint32
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HasCheckSum bool
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SingleSegment bool
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// asyncRunning indicates whether the async routine processes input on 'decoding'.
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asyncRunningMu sync.Mutex
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asyncRunning 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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var (
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frameMagic = []byte{0x28, 0xb5, 0x2f, 0xfd}
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skippableFrameMagic = []byte{0x2a, 0x4d, 0x18}
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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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default:
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return err
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case nil:
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signature[0] = b[0]
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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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default:
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return err
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case nil:
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copy(signature[1:], b)
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}
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if !bytes.Equal(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(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(int(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 !bytes.Equal(signature[:], frameMagic) {
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if debugDecoder {
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println("Got magic numbers: ", signature, "want:", 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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printf("raw: %x, mantissa: %d, exponent: %d\n", wd, wd&7, wd>>3)
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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 = nil
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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 size {
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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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if id > 0 {
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// ID 0 means "sorry, no dictionary anyway".
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// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#dictionary-format
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d.DictionaryID = &id
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}
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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 = 0
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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 fcsSize {
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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("field size bits:", v, "fcsSize:", fcsSize, "FrameContentSize:", d.FrameContentSize, hex.EncodeToString(b[:fcsSize]), "singleseg:", d.SingleSegment, "window:", d.WindowSize)
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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 == 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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}
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if d.WindowSize > uint64(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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// 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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d.history.maxSize = d.history.windowSize * 2
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} else {
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d.history.maxSize = d.history.windowSize + maxBlockSize
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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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printf("decoding new block %p:%p", block, block.data)
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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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d.sendErr(block, err)
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return err
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}
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block.input <- struct{}{}
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if debugDecoder {
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println("next block:", block)
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}
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d.asyncRunningMu.Lock()
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defer d.asyncRunningMu.Unlock()
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if !d.asyncRunning {
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return nil
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}
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if block.Last {
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// We indicate the frame is done by sending io.EOF
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d.decoding <- block
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return io.EOF
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}
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d.decoding <- block
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return nil
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}
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// sendEOF will queue an error block on the frame.
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// This will cause the frame decoder to return when it encounters the block.
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// Returns true if the decoder was added.
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func (d *frameDec) sendErr(block *blockDec, err error) bool {
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d.asyncRunningMu.Lock()
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defer d.asyncRunningMu.Unlock()
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if !d.asyncRunning {
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return false
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}
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println("sending error", err.Error())
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block.sendErr(err)
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d.decoding <- block
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return true
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}
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// checkCRC will check the checksum if 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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if !d.HasCheckSum {
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return nil
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}
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var tmp [4]byte
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got := d.crc.Sum64()
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// Flip to match file order.
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tmp[0] = byte(got >> 0)
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tmp[1] = byte(got >> 8)
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tmp[2] = byte(got >> 16)
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tmp[3] = byte(got >> 24)
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// We can overwrite upper tmp now
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want, 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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if !bytes.Equal(tmp[:], want) {
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if debugDecoder {
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println("CRC Check Failed:", tmp[:], "!=", 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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println("CRC ok", tmp[:])
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}
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return nil
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}
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func (d *frameDec) initAsync() {
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if !d.o.lowMem && !d.SingleSegment {
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// set max extra size history to 2MB.
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d.history.maxSize = d.history.windowSize + maxBlockSize
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}
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// re-alloc if more than one extra block size.
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if d.o.lowMem && cap(d.history.b) > d.history.maxSize+maxBlockSize {
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d.history.b = make([]byte, 0, d.history.maxSize)
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}
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if cap(d.history.b) < d.history.maxSize {
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d.history.b = make([]byte, 0, d.history.maxSize)
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}
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if cap(d.decoding) < d.o.concurrent {
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d.decoding = make(chan *blockDec, d.o.concurrent)
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}
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if debugDecoder {
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h := d.history
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printf("history init. len: %d, cap: %d", len(h.b), cap(h.b))
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}
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d.asyncRunningMu.Lock()
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d.asyncRunning = true
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d.asyncRunningMu.Unlock()
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}
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// startDecoder will start decoding blocks and write them to the writer.
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// The decoder will stop as soon as an error occurs or at end of frame.
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// When the frame has finished decoding the *bufio.Reader
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// containing the remaining input will be sent on frameDec.frameDone.
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func (d *frameDec) startDecoder(output chan decodeOutput) {
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written := int64(0)
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defer func() {
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d.asyncRunningMu.Lock()
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d.asyncRunning = false
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d.asyncRunningMu.Unlock()
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// Drain the currently decoding.
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d.history.error = true
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flushdone:
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for {
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select {
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case b := <-d.decoding:
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b.history <- &d.history
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output <- <-b.result
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default:
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break flushdone
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}
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}
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println("frame decoder done, signalling done")
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d.frameDone.Done()
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}()
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// Get decoder for first block.
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block := <-d.decoding
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block.history <- &d.history
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for {
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var next *blockDec
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// Get result
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r := <-block.result
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if r.err != nil {
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println("Result contained error", r.err)
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output <- r
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return
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}
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if debugDecoder {
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println("got result, from ", d.offset, "to", d.offset+int64(len(r.b)))
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d.offset += int64(len(r.b))
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}
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if !block.Last {
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// Send history to next block
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select {
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case next = <-d.decoding:
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if debugDecoder {
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println("Sending ", len(d.history.b), "bytes as history")
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}
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next.history <- &d.history
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default:
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// Wait until we have sent the block, so
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// other decoders can potentially get the decoder.
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next = nil
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}
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}
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// Add checksum, async to decoding.
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if d.HasCheckSum {
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n, err := d.crc.Write(r.b)
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if err != nil {
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r.err = err
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if n != len(r.b) {
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r.err = io.ErrShortWrite
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}
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output <- r
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return
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}
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}
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written += int64(len(r.b))
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if d.SingleSegment && uint64(written) > d.FrameContentSize {
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println("runDecoder: single segment and", uint64(written), ">", d.FrameContentSize)
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r.err = ErrFrameSizeExceeded
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output <- r
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return
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}
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if block.Last {
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r.err = d.checkCRC()
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output <- r
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return
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}
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output <- r
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if next == nil {
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// There was no decoder available, we wait for one now that we have sent to the writer.
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if debugDecoder {
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println("Sending ", len(d.history.b), " bytes as history")
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}
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next = <-d.decoding
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next.history <- &d.history
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}
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block = next
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}
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}
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// runDecoder will create a sync decoder that will decode a block of data.
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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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// Store input length, so we only check new data.
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crcStart := len(dst)
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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 || dec.Last {
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break
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}
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if uint64(len(d.history.b)) > d.o.maxDecodedSize {
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err = ErrDecoderSizeExceeded
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break
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}
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if d.SingleSegment && uint64(len(d.history.b)) > d.o.maxDecodedSize {
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println("runDecoder: single segment and", uint64(len(d.history.b)), ">", d.o.maxDecodedSize)
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err = ErrFrameSizeExceeded
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break
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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.HasCheckSum {
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var n int
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n, err = d.crc.Write(dst[crcStart:])
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if err == nil {
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if n != len(dst)-crcStart {
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err = io.ErrShortWrite
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} else {
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err = d.checkCRC()
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}
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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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