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|
//go:build windows || linux
// +build windows linux
package wim
import (
"encoding/binary"
"io"
"github.com/Microsoft/go-winio/wim/lzx"
)
const chunkSize = 32768 // Compressed resource chunk size
type compressedReader struct {
r *io.SectionReader
d io.ReadCloser
chunks []int64
curChunk int
originalSize int64
}
func newCompressedReader(r *io.SectionReader, originalSize int64, offset int64) (*compressedReader, error) {
nchunks := (originalSize + chunkSize - 1) / chunkSize
var base int64
chunks := make([]int64, nchunks)
if originalSize <= 0xffffffff {
// 32-bit chunk offsets
base = (nchunks - 1) * 4
chunks32 := make([]uint32, nchunks-1)
err := binary.Read(r, binary.LittleEndian, chunks32)
if err != nil {
return nil, err
}
for i, n := range chunks32 {
chunks[i+1] = int64(n)
}
} else {
// 64-bit chunk offsets
base = (nchunks - 1) * 8
err := binary.Read(r, binary.LittleEndian, chunks[1:])
if err != nil {
return nil, err
}
}
for i, c := range chunks {
chunks[i] = c + base
}
cr := &compressedReader{
r: r,
chunks: chunks,
originalSize: originalSize,
}
err := cr.reset(int(offset / chunkSize))
if err != nil {
return nil, err
}
suboff := offset % chunkSize
if suboff != 0 {
_, err := io.CopyN(io.Discard, cr.d, suboff)
if err != nil {
return nil, err
}
}
return cr, nil
}
func (r *compressedReader) chunkOffset(n int) int64 {
if n == len(r.chunks) {
return r.r.Size()
}
return r.chunks[n]
}
func (r *compressedReader) chunkSize(n int) int {
return int(r.chunkOffset(n+1) - r.chunkOffset(n))
}
func (r *compressedReader) uncompressedSize(n int) int {
if n < len(r.chunks)-1 {
return chunkSize
}
size := int(r.originalSize % chunkSize)
if size == 0 {
size = chunkSize
}
return size
}
func (r *compressedReader) reset(n int) error {
if n >= len(r.chunks) {
return io.EOF
}
if r.d != nil {
r.d.Close()
}
r.curChunk = n
size := r.chunkSize(n)
uncompressedSize := r.uncompressedSize(n)
section := io.NewSectionReader(r.r, r.chunkOffset(n), int64(size))
if size != uncompressedSize {
d, err := lzx.NewReader(section, uncompressedSize)
if err != nil {
return err
}
r.d = d
} else {
r.d = io.NopCloser(section)
}
return nil
}
func (r *compressedReader) Read(b []byte) (int, error) {
for {
n, err := r.d.Read(b)
if err != io.EOF { //nolint:errorlint
return n, err
}
err = r.reset(r.curChunk + 1)
if err != nil {
return n, err
}
}
}
func (r *compressedReader) Close() error {
var err error
if r.d != nil {
err = r.d.Close()
r.d = nil
}
return err
}
|
