github.com/shogo82148/std@v1.22.1-0.20240327122250-4e474527810c/internal/zstd/zstd.go (about)

     1  // Copyright 2023 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package zstd provides a decompressor for zstd streams,
     6  // described in RFC 8878. It does not support dictionaries.
     7  package zstd
     8  
     9  import (
    10  	"github.com/shogo82148/std/io"
    11  )
    12  
    13  // Reader implements [io.Reader] to read a zstd compressed stream.
    14  type Reader struct {
    15  	// The underlying Reader.
    16  	r io.Reader
    17  
    18  	// Whether we have read the frame header.
    19  	// This is of interest when buffer is empty.
    20  	// If true we expect to see a new block.
    21  	sawFrameHeader bool
    22  
    23  	// Whether the current frame expects a checksum.
    24  	hasChecksum bool
    25  
    26  	// Whether we have read at least one frame.
    27  	readOneFrame bool
    28  
    29  	// True if the frame size is not known.
    30  	frameSizeUnknown bool
    31  
    32  	// The number of uncompressed bytes remaining in the current frame.
    33  	// If frameSizeUnknown is true, this is not valid.
    34  	remainingFrameSize uint64
    35  
    36  	// The number of bytes read from r up to the start of the current
    37  	// block, for error reporting.
    38  	blockOffset int64
    39  
    40  	// Buffered decompressed data.
    41  	buffer []byte
    42  	// Current read offset in buffer.
    43  	off int
    44  
    45  	// The current repeated offsets.
    46  	repeatedOffset1 uint32
    47  	repeatedOffset2 uint32
    48  	repeatedOffset3 uint32
    49  
    50  	// The current Huffman tree used for compressing literals.
    51  	huffmanTable     []uint16
    52  	huffmanTableBits int
    53  
    54  	// The window for back references.
    55  	window window
    56  
    57  	// A buffer available to hold a compressed block.
    58  	compressedBuf []byte
    59  
    60  	// A buffer for literals.
    61  	literals []byte
    62  
    63  	// Sequence decode FSE tables.
    64  	seqTables    [3][]fseBaselineEntry
    65  	seqTableBits [3]uint8
    66  
    67  	// Buffers for sequence decode FSE tables.
    68  	seqTableBuffers [3][]fseBaselineEntry
    69  
    70  	// Scratch space used for small reads, to avoid allocation.
    71  	scratch [16]byte
    72  
    73  	// A scratch table for reading an FSE. Only temporarily valid.
    74  	fseScratch []fseEntry
    75  
    76  	// For checksum computation.
    77  	checksum xxhash64
    78  }
    79  
    80  // NewReader creates a new Reader that decompresses data from the given reader.
    81  func NewReader(input io.Reader) *Reader
    82  
    83  // Reset discards the current state and starts reading a new stream from r.
    84  // This permits reusing a Reader rather than allocating a new one.
    85  func (r *Reader) Reset(input io.Reader)
    86  
    87  // Read implements [io.Reader].
    88  func (r *Reader) Read(p []byte) (int, error)
    89  
    90  // ReadByte implements [io.ByteReader].
    91  func (r *Reader) ReadByte() (byte, error)