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// Copyright 2014-2022 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"
)
// uint32LE reads an uint32 integer from a byte slice
func uint32LE(b []byte) uint32 {
x := uint32(b[3]) << 24
x |= uint32(b[2]) << 16
x |= uint32(b[1]) << 8
x |= uint32(b[0])
return x
}
// uint64LE converts the uint64 value stored as little endian to an uint64
// value.
func uint64LE(b []byte) uint64 {
x := uint64(b[7]) << 56
x |= uint64(b[6]) << 48
x |= uint64(b[5]) << 40
x |= uint64(b[4]) << 32
x |= uint64(b[3]) << 24
x |= uint64(b[2]) << 16
x |= uint64(b[1]) << 8
x |= uint64(b[0])
return x
}
// putUint32LE puts an uint32 integer into a byte slice that must have at least
// a length of 4 bytes.
func putUint32LE(b []byte, x uint32) {
b[0] = byte(x)
b[1] = byte(x >> 8)
b[2] = byte(x >> 16)
b[3] = byte(x >> 24)
}
// putUint64LE puts the uint64 value into the byte slice as little endian
// value. The byte slice b must have at least place for 8 bytes.
func putUint64LE(b []byte, x uint64) {
b[0] = byte(x)
b[1] = byte(x >> 8)
b[2] = byte(x >> 16)
b[3] = byte(x >> 24)
b[4] = byte(x >> 32)
b[5] = byte(x >> 40)
b[6] = byte(x >> 48)
b[7] = byte(x >> 56)
}
// noHeaderSize defines the value of the length field in the LZMA header.
const noHeaderSize uint64 = 1<<64 - 1
// HeaderLen provides the length of the LZMA file header.
const HeaderLen = 13
// Header represents the Header of an LZMA file.
type Header struct {
Properties Properties
DictSize uint32
// uncompressed Size; negative value if no Size is given
Size int64
}
// marshalBinary marshals the header.
func (h *Header) marshalBinary() (data []byte, err error) {
if err = h.Properties.verify(); err != nil {
return nil, err
}
if !(h.DictSize <= MaxDictCap) {
return nil, fmt.Errorf("lzma: DictCap %d out of range",
h.DictSize)
}
data = make([]byte, 13)
// property byte
data[0] = h.Properties.Code()
// dictionary capacity
putUint32LE(data[1:5], uint32(h.DictSize))
// uncompressed size
var s uint64
if h.Size > 0 {
s = uint64(h.Size)
} else {
s = noHeaderSize
}
putUint64LE(data[5:], s)
return data, nil
}
// unmarshalBinary unmarshals the header.
func (h *Header) unmarshalBinary(data []byte) error {
if len(data) != HeaderLen {
return errors.New("lzma.unmarshalBinary: data has wrong length")
}
// properties
var err error
if h.Properties, err = PropertiesForCode(data[0]); err != nil {
return err
}
// dictionary capacity
h.DictSize = uint32LE(data[1:])
if int(h.DictSize) < 0 {
return errors.New(
"LZMA header: dictionary capacity exceeds maximum " +
"integer")
}
// uncompressed size
s := uint64LE(data[5:])
if s == noHeaderSize {
h.Size = -1
} else {
h.Size = int64(s)
if h.Size < 0 {
return errors.New(
"LZMA header: uncompressed size " +
"out of int64 range")
}
}
return nil
}
// validDictSize checks whether the dictionary capacity is correct. This
// is used to weed out wrong file headers.
func validDictSize(dictcap int) bool {
if int64(dictcap) == MaxDictCap {
return true
}
for n := uint(10); n < 32; n++ {
if dictcap == 1<<n {
return true
}
if dictcap == 1<<n+1<<(n-1) {
return true
}
}
return false
}
// ValidHeader checks for a valid LZMA file header. It allows only
// dictionary sizes of 2^n or 2^n+2^(n-1) with n >= 10 or 2^32-1. If
// there is an explicit size it must not exceed 256 GiB. The length of
// the data argument must be HeaderLen.
//
// This function should be disregarded because there is no guarantee that LZMA
// files follow the constraints.
func ValidHeader(data []byte) bool {
var h Header
if err := h.unmarshalBinary(data); err != nil {
return false
}
if !validDictSize(int(h.DictSize)) {
return false
}
return h.Size < 0 || h.Size <= 1<<38
}
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