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package zstd
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"io"
"github.com/klauspost/compress/huff0"
)
type dict struct {
id uint32
litDec *huff0.Scratch
llDec, ofDec, mlDec sequenceDec
offsets [3]int
content []byte
}
var dictMagic = [4]byte{0x37, 0xa4, 0x30, 0xec}
// Load a dictionary as described in
// https://github.com/facebook/zstd/blob/master/doc/zstd_compression_format.md#dictionary-format
func loadDict(b []byte) (*dict, error) {
// Check static field size.
if len(b) <= 8+(3*4) {
return nil, io.ErrUnexpectedEOF
}
d := dict{
llDec: sequenceDec{fse: &fseDecoder{}},
ofDec: sequenceDec{fse: &fseDecoder{}},
mlDec: sequenceDec{fse: &fseDecoder{}},
}
if !bytes.Equal(b[:4], dictMagic[:]) {
return nil, ErrMagicMismatch
}
d.id = binary.LittleEndian.Uint32(b[4:8])
if d.id == 0 {
return nil, errors.New("dictionaries cannot have ID 0")
}
// Read literal table
var err error
d.litDec, b, err = huff0.ReadTable(b[8:], nil)
if err != nil {
return nil, err
}
br := byteReader{
b: b,
off: 0,
}
readDec := func(i tableIndex, dec *fseDecoder) error {
if err := dec.readNCount(&br, uint16(maxTableSymbol[i])); err != nil {
return err
}
if br.overread() {
return io.ErrUnexpectedEOF
}
err = dec.transform(symbolTableX[i])
if err != nil {
println("Transform table error:", err)
return err
}
if debug {
println("Read table ok", "symbolLen:", dec.symbolLen)
}
// Set decoders as predefined so they aren't reused.
dec.preDefined = true
return nil
}
if err := readDec(tableOffsets, d.ofDec.fse); err != nil {
return nil, err
}
if err := readDec(tableMatchLengths, d.mlDec.fse); err != nil {
return nil, err
}
if err := readDec(tableLiteralLengths, d.llDec.fse); err != nil {
return nil, err
}
if br.remain() < 12 {
return nil, io.ErrUnexpectedEOF
}
d.offsets[0] = int(br.Uint32())
br.advance(4)
d.offsets[1] = int(br.Uint32())
br.advance(4)
d.offsets[2] = int(br.Uint32())
br.advance(4)
if d.offsets[0] <= 0 || d.offsets[1] <= 0 || d.offsets[2] <= 0 {
return nil, errors.New("invalid offset in dictionary")
}
d.content = make([]byte, br.remain())
copy(d.content, br.unread())
if d.offsets[0] > len(d.content) || d.offsets[1] > len(d.content) || d.offsets[2] > len(d.content) {
return nil, fmt.Errorf("initial offset bigger than dictionary content size %d, offsets: %v", len(d.content), d.offsets)
}
return &d, nil
}
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