// readFilter reads a block filter from the block header. At this point
// in time only the LZMA2 filter is supported.
func readFilter(r io.Reader) (f filter, err error) {
br := lzma.ByteReader(r)
// index
id, _, err := readUvarint(br)
if err != nil {
return nil, err
}
var data []byte
switch id {
case lzmaFilterID:
data = make([]byte, lzmaFilterLen)
data[0] = lzmaFilterID
if _, err = io.ReadFull(r, data[1:]); err != nil {
return nil, err
}
f = new(lzmaFilter)
default:
if id >= minReservedID {
return nil, errors.New(
"xz: reserved filter id in block stream header")
}
return nil, errors.New("xz: invalid filter id")
}
if err = f.UnmarshalBinary(data); err != nil {
return nil, err
}
return f, err
}
// readIndexBody reads the index from the reader. It assumes that the
// index indicator has already been read.
func readIndexBody(r io.Reader) (records []record, n int64, err error) {
crc := crc32.NewIEEE()
// index indicator
crc.Write([]byte{0})
br := lzma.ByteReader(io.TeeReader(r, crc))
// number of records
u, k, err := readUvarint(br)
n += int64(k)
if err != nil {
return nil, n, err
}
recLen := int(u)
if recLen < 0 || uint64(recLen) != u {
return nil, n, errors.New("xz: record number overflow")
}
// list of records
records = make([]record, recLen)
for i := range records {
records[i], k, err = readRecord(br)
n += int64(k)
if err != nil {
return nil, n, err
}
}
p := make([]byte, padLen(int64(n+1)), 4)
k, err = io.ReadFull(br.(io.Reader), p)
n += int64(k)
if err != nil {
return nil, n, err
}
if !allZeros(p) {
return nil, n, errors.New("xz: non-zero byte in index padding")
}
// crc32
s := crc.Sum32()
p = p[:4]
k, err = io.ReadFull(br.(io.Reader), p)
n += int64(k)
if err != nil {
return records, n, err
}
if uint32LE(p) != s {
return nil, n, errors.New("xz: wrong checksum for index")
}
return records, n, nil
}