Function loadDict

zstd/dict.go:71–150

Load a dictionary as described in https://github.com/facebook/zstd/blob/master/doc/zstd_compression_format.md#dictionary-format

(b []byte)

// 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 string(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.litEnc, b, err = huff0.ReadTable(b[8:], nil)
	if err != nil {
		return nil, fmt.Errorf("loading literal table: %w", err)
	}
	d.litEnc.Reuse = huff0.ReusePolicyMust

	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 debugDecoder || debugEncoder {
			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