It comes in the form of a GlueHints object (see glue_hints.[h|cc]), which is created with a source delegation packet. This gets passed on to addCallback, and if the NSAS notices it has to do work (i.e. it does not have data available), it'll use the glue (if that is available).

Changed on argument shared_ptr ref to a normal shared_ptr in NamserverAddress constructor; need the refcount to be incremented.