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compress.go
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compress.go
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// Copyright 2018 The go-hep Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package rootio
import (
"compress/zlib"
"io"
"github.com/pierrec/lz4"
"github.com/ulikunitz/xz"
)
func rootCompressAlg(buf [rootHDRSIZE]byte) compressAlgType {
switch {
case buf[0] == 'Z' && buf[1] == 'L':
return kZLIB
case buf[0] == 'X' && buf[1] == 'Z':
return kLZMA
case buf[0] == 'L' && buf[1] == '4':
return kLZ4
case buf[0] == 'C' && buf[1] == 'S':
return kOldCompressionAlgo
default:
return kUndefinedCompressionAlgorithm
}
}
func decompress(r io.Reader, buf []byte) error {
var (
beg = 0
end = 0
buflen = len(buf)
)
for end < buflen {
var hdr [rootHDRSIZE]byte
_, err := io.ReadFull(r, hdr[:])
if err != nil {
return err
}
srcsz := (int64(hdr[3]) | int64(hdr[4])<<8 | int64(hdr[5])<<16)
tgtsz := int64(hdr[6]) | int64(hdr[7])<<8 | int64(hdr[8])<<16
end += int(tgtsz)
lr := io.LimitReader(r, srcsz)
switch rootCompressAlg(hdr) {
case kZLIB:
rc, err := zlib.NewReader(lr)
if err != nil {
return err
}
defer rc.Close()
_, err = io.ReadFull(rc, buf[beg:end])
if err != nil {
return err
}
case kLZ4:
src := make([]byte, srcsz)
_, err = io.ReadFull(lr, src)
if err != nil {
return err
}
const chksum = 8
// FIXME: we skip the 32b checksum. use it!
_, err = lz4.UncompressBlock(src[chksum:], buf[beg:end])
if err != nil {
return err
}
case kLZMA:
rc, err := xz.NewReader(lr)
if err != nil {
return err
}
_, err = io.ReadFull(rc, buf[beg:end])
if err != nil {
return err
}
default:
panic("rootio: unknown compression algorithm")
}
beg = end
}
return nil
}