Expert allows the serialisation of parts to occur separately from the writing of parts. While you are able to write any bigstring to the pipe rpc with this interface, you should only write state parts until you finalise the state, and then after that you should only write update parts.
val create_state_part :
state_bin_writer:'state_part Core.Bin_prot.Type_class.writer ->
'state_part ->
Core.Bigstring.tval finalise_state_message : Core.Bigstring.t lazy_tval create_update_part :
update_bin_writer:'update_part Core.Bin_prot.Type_class.writer ->
'update_part ->
Core.Bigstring.tval finalise_update_message : Core.Bigstring.t lazy_tval write_without_pushback :
?pos:int ->
?len:int ->
(_, _) t ->
Core.Bigstring.t ->
[ `Closed | `Ok ]