func (lg *logger) next() ([]byte, bool, error) {
if lg.pos+_OF_DATA >= lg.fileSize {
return nil, false, nil
}
tmp := make([]byte, 4)
_, err := lg.file.ReadAt(tmp, lg.pos)
if err != nil {
return nil, false, err
}
size := int64(utils.ParseUint32(tmp))
if lg.pos+size+_OF_DATA > lg.fileSize {
return nil, false, nil // bad tail
}
log := make([]byte, _OF_DATA+size)
_, err = lg.file.ReadAt(log, lg.pos)
if err != nil {
return nil, false, err
}
checksum1 := calChecksum(0, log[_OF_DATA:])
checksum2 := utils.ParseUint32(log[_OF_CHECKSUM:])
if checksum1 != checksum2 {
return nil, false, nil // bad tail
}
lg.pos += int64(len(log))
return log, true, nil
}
func (lg *logger) init() error {
info, err := lg.file.Stat()
if err != nil {
return err
}
fileSize := info.Size()
if fileSize < 4 {
return ErrBadLogFile
}
raw := make([]byte, 4)
_, err = lg.file.ReadAt(raw, 0)
if err != nil {
return err
}
xChecksum := utils.ParseUint32(raw)
lg.fileSize = fileSize
lg.xChecksum = xChecksum
return lg.checkAndRemoveTail()
}