// Opens a space for reading given a reader, and an offset/length of
// the spaces position within the file.
func openSpace(reader io.ReadSeeker, id []byte, offset, length int64) *Space {
if st, err := findSpaceIndex(reader, offset, length); err == nil {
return &Space{
Id: id,
index: st,
reader: reader,
blocks: blocks.NewReader(reader, 4096),
offset: offset,
length: length,
}
}
return nil
}
// Finds and returns an index by it's name and value.
func (s *Space) findIndex(name, value string) *blocks.Reader {
if val, err := s.index.Get([]byte("i" + name + ":" + value)); err == nil {
// The entry in the SSTable index for indexes
// is variable length integers integers for the
// offset and length of the index within
// the file. In this case, we just need the
// offset to find it's starting point.
offset := binary.ReadUvarint(bytes.NewReader(val))
// An index is block encoded, so fire up
// a block reader, and seek to the start
// of the index.
reader := blocks.NewReader(s.reader, 4096)
reader.Seek(s.offset+offset, 0)
return reader
}
return nil
}