1// Copyright 2014-2022 Ulrich Kunitz. 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 lzma supports the decoding and encoding of LZMA streams.
  6// Reader and Writer support the classic LZMA format. Reader2 and
  7// Writer2 support the decoding and encoding of LZMA2 streams.
  8//
  9// The package is written completely in Go and doesn't rely on any external
 10// library.
 11package lzma
 12
 13import (
 14	"errors"
 15	"io"
 16)
 17
 18// ReaderConfig stores the parameters for the reader of the classic LZMA
 19// format.
 20type ReaderConfig struct {
 21	DictCap int
 22}
 23
 24// fill converts the zero values of the configuration to the default values.
 25func (c *ReaderConfig) fill() {
 26	if c.DictCap == 0 {
 27		c.DictCap = 8 * 1024 * 1024
 28	}
 29}
 30
 31// Verify checks the reader configuration for errors. Zero values will
 32// be replaced by default values.
 33func (c *ReaderConfig) Verify() error {
 34	c.fill()
 35	if !(MinDictCap <= c.DictCap && int64(c.DictCap) <= MaxDictCap) {
 36		return errors.New("lzma: dictionary capacity is out of range")
 37	}
 38	return nil
 39}
 40
 41// Reader provides a reader for LZMA files or streams.
 42type Reader struct {
 43	lzma io.Reader
 44	h    header
 45	d    *decoder
 46}
 47
 48// NewReader creates a new reader for an LZMA stream using the classic
 49// format. NewReader reads and checks the header of the LZMA stream.
 50func NewReader(lzma io.Reader) (r *Reader, err error) {
 51	return ReaderConfig{}.NewReader(lzma)
 52}
 53
 54// NewReader creates a new reader for an LZMA stream in the classic
 55// format. The function reads and verifies the the header of the LZMA
 56// stream.
 57func (c ReaderConfig) NewReader(lzma io.Reader) (r *Reader, err error) {
 58	if err = c.Verify(); err != nil {
 59		return nil, err
 60	}
 61	data := make([]byte, HeaderLen)
 62	if _, err := io.ReadFull(lzma, data); err != nil {
 63		if err == io.EOF {
 64			return nil, errors.New("lzma: unexpected EOF")
 65		}
 66		return nil, err
 67	}
 68	r = &Reader{lzma: lzma}
 69	if err = r.h.unmarshalBinary(data); err != nil {
 70		return nil, err
 71	}
 72	if r.h.dictCap < MinDictCap {
 73		r.h.dictCap = MinDictCap
 74	}
 75	dictCap := r.h.dictCap
 76	if c.DictCap > dictCap {
 77		dictCap = c.DictCap
 78	}
 79
 80	state := newState(r.h.properties)
 81	dict, err := newDecoderDict(dictCap)
 82	if err != nil {
 83		return nil, err
 84	}
 85	r.d, err = newDecoder(ByteReader(lzma), state, dict, r.h.size)
 86	if err != nil {
 87		return nil, err
 88	}
 89	return r, nil
 90}
 91
 92// EOSMarker indicates that an EOS marker has been encountered.
 93func (r *Reader) EOSMarker() bool {
 94	return r.d.eosMarker
 95}
 96
 97// Read returns uncompressed data.
 98func (r *Reader) Read(p []byte) (n int, err error) {
 99	return r.d.Read(p)
100}