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reader.go
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reader.go
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package huffman
import (
"bufio"
"errors"
"fmt"
"io"
)
var (
ErrHuffmanDecompress = errors.New("decompression error")
)
type Reader struct {
d *Dictionary
br io.ByteReader
bufSize int
}
// New creates a new Reader with the default Teeworlds' dictionary.
func NewReader(r io.Reader) *Reader {
// pass default global dictionary that is used in Teeworlds
return NewReaderDict(DefaultDictionary, r)
}
// NewReaderDict expects a Dictionary (index -> symbol)
// You can use the default one if you just want to work with Teeworlds' default compression.
func NewReaderDict(d *Dictionary, r io.Reader) *Reader {
var bufSize = 2048
br, ok := r.(io.ByteReader)
if !ok {
br = bufio.NewReaderSize(r, bufSize)
}
h := Reader{
d: d,
br: br,
bufSize: bufSize,
}
return &h
}
// Decompress decompresses 'data' and writes the result into 'decompressed'.
// The decompressed slice must be preallocated to fit the decompressed data.
// Read is the size that was decompressed and written into the 'decompressed' slice.
func (r *Reader) Read(decompressed []byte) (read int, err error) {
// read from underlying reader
var (
cursor = 0
dstEnd = len(decompressed)
bits uint32
bitCount uint8
eof *node = &r.d.nodes[EofSymbol]
n *node = nil
b byte
)
for cursor = 0; cursor < dstEnd; cursor++ {
n = nil
if bitCount >= lookupTableBits {
n = r.d.decodeLut[bits&lookupTableMask]
}
for bitCount < 24 {
b, err = r.br.ReadByte()
if err != nil {
if errors.Is(err, io.EOF) {
break
}
// unexpected error, abort
return cursor, err
}
bits |= uint32(b) << bitCount
bitCount += 8
}
if n == nil {
n = r.d.decodeLut[bits&lookupTableMask]
}
if n == nil {
return cursor, fmt.Errorf("%w: decoding error: symbol not found in lookup table: %x (masked: %x)", ErrHuffmanDecompress, bits, bits&lookupTableMask)
}
if n.NumBits > 0 {
// leaf nodes
bits >>= n.NumBits
bitCount -= n.NumBits
} else {
bits >>= lookupTableBits
bitCount -= lookupTableBits
// walk the tree bit by bit
for {
// traverse tree
n = &r.d.nodes[n.Leafs[bits&1]]
// remove bit
bitCount--
bits >>= 1
// check if we hit a symbol
if n.NumBits > 0 {
break
}
if bitCount == 0 {
return cursor, fmt.Errorf("%w: decoding error: symbol not found in tree", ErrHuffmanDecompress)
}
}
}
if n == eof {
break
}
decompressed[cursor] = n.Symbol
}
return cursor, io.EOF
}
func (r *Reader) Reset(rr io.Reader) {
// bufio.Reader implements this interface
br, ok := rr.(io.ByteReader)
if ok {
r.br = br
return
}
r.br = bufio.NewReaderSize(rr, r.bufSize)
}