read
Reads a group.
This method allocates and returns a new ByteBuf. It is the caller's responsibility to release the ByteBuf.
Return
the contents of the group.
Parameters
archive
the archive ID.
group
the group ID.
Throws
if the archive or group ID is out of bounds.
if the archive or group does not exist.
if the store is corrupt.
if an underlying I/O error occurs.