// readAll read entire referenced block.
func (p *bInfo) readAll(r io.ReaderAt, checksum bool) (b []byte, err error) {
raw := make([]byte, p.size+5)
_, err = readFullAt(r, raw, int64(p.offset))
if err != nil {
return
}
crcb := raw[len(raw)-4:]
raw = raw[:len(raw)-4]
if checksum {
sum := binary.LittleEndian.Uint32(crcb)
sum = hash.UnmaskCRC32(sum)
crc := hash.NewCRC32C()
crc.Write(raw)
if crc.Sum32() != sum {
err = errors.ErrCorrupt("block checksum mismatch")
return
}
}
compression := raw[len(raw)-1]
b = raw[:len(raw)-1]
switch compression {
case kNoCompression:
case kSnappyCompression:
return snappy.Decode(nil, b)
default:
err = errors.ErrCorrupt("bad block type")
}
return
}
func (r *Reader) read() (ret []byte, rtype uint, err error) {
retry:
if len(r.buf) < kHeaderSize {
if r.eof {
if len(r.buf) > 0 {
r.drop(len(r.buf), "truncated record at end of file")
r.rbuf = nil
r.buf = nil
}
rtype = tEof
return
}
if r.rbuf == nil {
r.rbuf = make([]byte, BlockSize)
} else {
r.off++
}
var n int
n, err = r.r.ReadAt(r.rbuf, int64(r.off)*BlockSize)
if err != nil {
if err == io.EOF {
err = nil
} else {
return
}
}
r.buf = r.rbuf[:n]
if n < BlockSize {
r.eof = true
goto retry
}
}
// decode record length and type
recLen := int(r.buf[4]) | (int(r.buf[5]) << 8)
rtype = uint(r.buf[6])
// check whether the header is sane
if len(r.buf) < kHeaderSize+recLen || rtype > tLast {
rtype = tCorrupt
r.drop(len(r.buf), "header corrupted")
} else if r.checksum {
// decode the checksum
recCrc := hash.UnmaskCRC32(binary.LittleEndian.Uint32(r.buf))
crc := hash.NewCRC32C()
crc.Write(r.buf[6 : kHeaderSize+recLen])
if crc.Sum32() != recCrc {
// Drop the rest of the buffer since "length" itself may have
// been corrupted and if we trust it, we could find some
// fragment of a real journal record that just happens to look
// like a valid journal record.
rtype = tCorrupt
r.drop(len(r.buf), "checksum mismatch")
}
}
if rtype == tCorrupt {
// report bytes drop
r.buf = nil
} else {
ret = r.buf[kHeaderSize : kHeaderSize+recLen]
r.buf = r.buf[kHeaderSize+recLen:]
}
return
}