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forgejo/vendor/github.com/ulikunitz/xz/lzma/header2.go

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// Copyright 2014-2021 Ulrich Kunitz. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package lzma
import (
"errors"
"fmt"
"io"
)
const (
// maximum size of compressed data in a chunk
maxCompressed = 1 << 16
// maximum size of uncompressed data in a chunk
maxUncompressed = 1 << 21
)
// chunkType represents the type of an LZMA2 chunk. Note that this
// value is an internal representation and no actual encoding of a LZMA2
// chunk header.
type chunkType byte
// Possible values for the chunk type.
const (
// end of stream
cEOS chunkType = iota
// uncompressed; reset dictionary
cUD
// uncompressed; no reset of dictionary
cU
// LZMA compressed; no reset
cL
// LZMA compressed; reset state
cLR
// LZMA compressed; reset state; new property value
cLRN
// LZMA compressed; reset state; new property value; reset dictionary
cLRND
)
// chunkTypeStrings provide a string representation for the chunk types.
var chunkTypeStrings = [...]string{
cEOS: "EOS",
cU: "U",
cUD: "UD",
cL: "L",
cLR: "LR",
cLRN: "LRN",
cLRND: "LRND",
}
// String returns a string representation of the chunk type.
func (c chunkType) String() string {
if !(cEOS <= c && c <= cLRND) {
return "unknown"
}
return chunkTypeStrings[c]
}
// Actual encodings for the chunk types in the value. Note that the high
// uncompressed size bits are stored in the header byte additionally.
const (
hEOS = 0
hUD = 1
hU = 2
hL = 1 << 7
hLR = 1<<7 | 1<<5
hLRN = 1<<7 | 1<<6
hLRND = 1<<7 | 1<<6 | 1<<5
)
// errHeaderByte indicates an unsupported value for the chunk header
// byte. These bytes starts the variable-length chunk header.
var errHeaderByte = errors.New("lzma: unsupported chunk header byte")
// headerChunkType converts the header byte into a chunk type. It
// ignores the uncompressed size bits in the chunk header byte.
func headerChunkType(h byte) (c chunkType, err error) {
if h&hL == 0 {
// no compression
switch h {
case hEOS:
c = cEOS
case hUD:
c = cUD
case hU:
c = cU
default:
return 0, errHeaderByte
}
return
}
switch h & hLRND {
case hL:
c = cL
case hLR:
c = cLR
case hLRN:
c = cLRN
case hLRND:
c = cLRND
default:
return 0, errHeaderByte
}
return
}
// uncompressedHeaderLen provides the length of an uncompressed header
const uncompressedHeaderLen = 3
// headerLen returns the length of the LZMA2 header for a given chunk
// type.
func headerLen(c chunkType) int {
switch c {
case cEOS:
return 1
case cU, cUD:
return uncompressedHeaderLen
case cL, cLR:
return 5
case cLRN, cLRND:
return 6
}
panic(fmt.Errorf("unsupported chunk type %d", c))
}
// chunkHeader represents the contents of a chunk header.
type chunkHeader struct {
ctype chunkType
uncompressed uint32
compressed uint16
props Properties
}
// String returns a string representation of the chunk header.
func (h *chunkHeader) String() string {
return fmt.Sprintf("%s %d %d %s", h.ctype, h.uncompressed,
h.compressed, &h.props)
}
// UnmarshalBinary reads the content of the chunk header from the data
// slice. The slice must have the correct length.
func (h *chunkHeader) UnmarshalBinary(data []byte) error {
if len(data) == 0 {
return errors.New("no data")
}
c, err := headerChunkType(data[0])
if err != nil {
return err
}
n := headerLen(c)
if len(data) < n {
return errors.New("incomplete data")
}
if len(data) > n {
return errors.New("invalid data length")
}
*h = chunkHeader{ctype: c}
if c == cEOS {
return nil
}
h.uncompressed = uint32(uint16BE(data[1:3]))
if c <= cU {
return nil
}
h.uncompressed |= uint32(data[0]&^hLRND) << 16
h.compressed = uint16BE(data[3:5])
if c <= cLR {
return nil
}
h.props, err = PropertiesForCode(data[5])
return err
}
// MarshalBinary encodes the chunk header value. The function checks
// whether the content of the chunk header is correct.
func (h *chunkHeader) MarshalBinary() (data []byte, err error) {
if h.ctype > cLRND {
return nil, errors.New("invalid chunk type")
}
if err = h.props.verify(); err != nil {
return nil, err
}
data = make([]byte, headerLen(h.ctype))
switch h.ctype {
case cEOS:
return data, nil
case cUD:
data[0] = hUD
case cU:
data[0] = hU
case cL:
data[0] = hL
case cLR:
data[0] = hLR
case cLRN:
data[0] = hLRN
case cLRND:
data[0] = hLRND
}
putUint16BE(data[1:3], uint16(h.uncompressed))
if h.ctype <= cU {
return data, nil
}
data[0] |= byte(h.uncompressed>>16) &^ hLRND
putUint16BE(data[3:5], h.compressed)
if h.ctype <= cLR {
return data, nil
}
data[5] = h.props.Code()
return data, nil
}
// readChunkHeader reads the chunk header from the IO reader.
func readChunkHeader(r io.Reader) (h *chunkHeader, err error) {
p := make([]byte, 1, 6)
if _, err = io.ReadFull(r, p); err != nil {
return
}
c, err := headerChunkType(p[0])
if err != nil {
return
}
p = p[:headerLen(c)]
if _, err = io.ReadFull(r, p[1:]); err != nil {
return
}
h = new(chunkHeader)
if err = h.UnmarshalBinary(p); err != nil {
return nil, err
}
return h, nil
}
// uint16BE converts a big-endian uint16 representation to an uint16
// value.
func uint16BE(p []byte) uint16 {
return uint16(p[0])<<8 | uint16(p[1])
}
// putUint16BE puts the big-endian uint16 presentation into the given
// slice.
func putUint16BE(p []byte, x uint16) {
p[0] = byte(x >> 8)
p[1] = byte(x)
}
// chunkState is used to manage the state of the chunks
type chunkState byte
// start and stop define the initial and terminating state of the chunk
// state
const (
start chunkState = 'S'
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stop chunkState = 'T'
)
// errors for the chunk state handling
var (
errChunkType = errors.New("lzma: unexpected chunk type")
errState = errors.New("lzma: wrong chunk state")
)
// next transitions state based on chunk type input
func (c *chunkState) next(ctype chunkType) error {
switch *c {
// start state
case 'S':
switch ctype {
case cEOS:
*c = 'T'
case cUD:
*c = 'R'
case cLRND:
*c = 'L'
default:
return errChunkType
}
// normal LZMA mode
case 'L':
switch ctype {
case cEOS:
*c = 'T'
case cUD:
*c = 'R'
case cU:
*c = 'U'
case cL, cLR, cLRN, cLRND:
break
default:
return errChunkType
}
// reset required
case 'R':
switch ctype {
case cEOS:
*c = 'T'
case cUD, cU:
break
case cLRN, cLRND:
*c = 'L'
default:
return errChunkType
}
// uncompressed
case 'U':
switch ctype {
case cEOS:
*c = 'T'
case cUD:
*c = 'R'
case cU:
break
case cL, cLR, cLRN, cLRND:
*c = 'L'
default:
return errChunkType
}
// terminal state
case 'T':
return errChunkType
default:
return errState
}
return nil
}
// defaultChunkType returns the default chunk type for each chunk state.
func (c chunkState) defaultChunkType() chunkType {
switch c {
case 'S':
return cLRND
case 'L', 'U':
return cL
case 'R':
return cLRN
default:
// no error
return cEOS
}
}
// maxDictCap defines the maximum dictionary capacity supported by the
// LZMA2 dictionary capacity encoding.
const maxDictCap = 1<<32 - 1
// maxDictCapCode defines the maximum dictionary capacity code.
const maxDictCapCode = 40
// The function decodes the dictionary capacity byte, but doesn't change
// for the correct range of the given byte.
func decodeDictCap(c byte) int64 {
return (2 | int64(c)&1) << (11 + (c>>1)&0x1f)
}
// DecodeDictCap decodes the encoded dictionary capacity. The function
// returns an error if the code is out of range.
func DecodeDictCap(c byte) (n int64, err error) {
if c >= maxDictCapCode {
if c == maxDictCapCode {
return maxDictCap, nil
}
return 0, errors.New("lzma: invalid dictionary size code")
}
return decodeDictCap(c), nil
}
// EncodeDictCap encodes a dictionary capacity. The function returns the
// code for the capacity that is greater or equal n. If n exceeds the
// maximum support dictionary capacity, the maximum value is returned.
func EncodeDictCap(n int64) byte {
a, b := byte(0), byte(40)
for a < b {
c := a + (b-a)>>1
m := decodeDictCap(c)
if n <= m {
if n == m {
return c
}
b = c
} else {
a = c + 1
}
}
return a
}