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@ -5,6 +5,7 @@ package zstd
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import (
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"bytes"
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"encoding/binary"
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"errors"
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"io"
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)
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@ -15,18 +16,50 @@ const HeaderMaxSize = 14 + 3
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// Header contains information about the first frame and block within that.
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type Header struct {
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// Window Size the window of data to keep while decoding.
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// Will only be set if HasFCS is false.
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WindowSize uint64
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// SingleSegment specifies whether the data is to be decompressed into a
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// single contiguous memory segment.
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// It implies that WindowSize is invalid and that FrameContentSize is valid.
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SingleSegment bool
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// Frame content size.
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// Expected size of the entire frame.
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FrameContentSize uint64
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// WindowSize is the window of data to keep while decoding.
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// Will only be set if SingleSegment is false.
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WindowSize uint64
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// Dictionary ID.
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// If 0, no dictionary.
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DictionaryID uint32
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// HasFCS specifies whether FrameContentSize has a valid value.
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HasFCS bool
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// FrameContentSize is the expected uncompressed size of the entire frame.
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FrameContentSize uint64
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// Skippable will be true if the frame is meant to be skipped.
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// This implies that FirstBlock.OK is false.
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Skippable bool
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// SkippableID is the user-specific ID for the skippable frame.
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// Valid values are between 0 to 15, inclusive.
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SkippableID int
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// SkippableSize is the length of the user data to skip following
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// the header.
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SkippableSize uint32
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// HeaderSize is the raw size of the frame header.
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//
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// For normal frames, it includes the size of the magic number and
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// the size of the header (per section 3.1.1.1).
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// It does not include the size for any data blocks (section 3.1.1.2) nor
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// the size for the trailing content checksum.
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//
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// For skippable frames, this counts the size of the magic number
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// along with the size of the size field of the payload.
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// It does not include the size of the skippable payload itself.
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// The total frame size is the HeaderSize plus the SkippableSize.
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HeaderSize int
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// First block information.
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FirstBlock struct {
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// OK will be set if first block could be decoded.
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@ -51,17 +84,9 @@ type Header struct {
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CompressedSize int
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}
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// Skippable will be true if the frame is meant to be skipped.
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// No other information will be populated.
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Skippable bool
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// If set there is a checksum present for the block content.
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// The checksum field at the end is always 4 bytes long.
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HasCheckSum bool
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// If this is true FrameContentSize will have a valid value
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HasFCS bool
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SingleSegment bool
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}
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// Decode the header from the beginning of the stream.
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@ -71,39 +96,46 @@ type Header struct {
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// If there isn't enough input, io.ErrUnexpectedEOF is returned.
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// The FirstBlock.OK will indicate if enough information was available to decode the first block header.
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func (h *Header) Decode(in []byte) error {
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*h = Header{}
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if len(in) < 4 {
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return io.ErrUnexpectedEOF
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}
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h.HeaderSize += 4
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b, in := in[:4], in[4:]
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if !bytes.Equal(b, frameMagic) {
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if !bytes.Equal(b[1:4], skippableFrameMagic) || b[0]&0xf0 != 0x50 {
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return ErrMagicMismatch
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}
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*h = Header{Skippable: true}
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if len(in) < 4 {
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return io.ErrUnexpectedEOF
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}
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h.HeaderSize += 4
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h.Skippable = true
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h.SkippableID = int(b[0] & 0xf)
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h.SkippableSize = binary.LittleEndian.Uint32(in)
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return nil
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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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if len(in) < 1 {
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return io.ErrUnexpectedEOF
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}
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// Clear output
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*h = Header{}
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fhd, in := in[0], in[1:]
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h.HeaderSize++
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h.SingleSegment = fhd&(1<<5) != 0
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h.HasCheckSum = fhd&(1<<2) != 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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if !h.SingleSegment {
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if len(in) < 1 {
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return io.ErrUnexpectedEOF
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}
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var wd byte
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wd, in = in[0], in[1:]
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h.HeaderSize++
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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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@ -120,9 +152,7 @@ func (h *Header) Decode(in []byte) error {
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return io.ErrUnexpectedEOF
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}
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b, in = in[:size], in[size:]
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if b == nil {
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return io.ErrUnexpectedEOF
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}
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h.HeaderSize += int(size)
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switch size {
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case 1:
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h.DictionaryID = uint32(b[0])
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@ -152,9 +182,7 @@ func (h *Header) Decode(in []byte) error {
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return io.ErrUnexpectedEOF
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}
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b, in = in[:fcsSize], in[fcsSize:]
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if b == nil {
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return io.ErrUnexpectedEOF
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}
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h.HeaderSize += int(fcsSize)
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switch fcsSize {
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case 1:
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h.FrameContentSize = uint64(b[0])
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dependabot[bot]
2 years ago
committed by
GitHub