library BlobLib;

type
  TISC_BlobGetSegment = function( BlobHandle : pointer; Buffer : pAnsiChar; BufferSize : word; var ResultSize : word ) : integer; cdecl;
  TISC_BlobPutSegment = procedure( BlobHandle : pointer; Buffer : pAnsiChar; BufferSize : integer ); cdecl;

  TBlob = packed record
            GetSegment     : TISC_BlobGetSegment;
            BlobHandle     : pointer;
            SegmentCount   : integer;
            MaxSegmentSize : integer;
            TotalSize      : integer;
            PutSegment     : TISC_BlobPutSegment;
          end;

function BlobFunc( var Blob: TBlob ) : integer; cdecl; export;
begin
  Result := 1;
end;

exports
  BlobFunc;

end.

declare external function BLOB_FUNC
    blob
returns integer by value
entry_point 'BlobFunc' module_name 'BlobLib.dll';

create table BLOB_DATA (
    ID   integer,
    DAT  blob sub_type 0 segment size 80
);

insert into BLOB_DATA ( ID, DAT ) values( 1, 'BLOB TEXT' );
commit;

SET TERM ^ ;

create or alter procedure BLOB_PROC
as
  declare variable B blob;
  declare variable I integer;
begin
  select DAT
    from BLOB_DATA
   where ID = 1
    into :B;
  I = BLOB_FUNC( :B );
end ^

set term ; ^

Error Message:
----------------------------------------
Unsuccessful execution caused by system error that does not preclude successful execution of subsequent statements.
feature is not supported.
BLOB and array data types are not supported for conversion operation.


[0053E3E7] FIB.IBError (Line 539, "FIB.pas" + 55) + $2
[00527353] FIBQuery.TFIBQuery.Next (Line 3134, "FIBQuery.pas" + 23) + $C
[00D9BF6F] DebugSP_New.TfrmDebugSP_new.ExecuteStatement (Line 1523, "DebugSP_New.pas" + 13) + $5

  I = BLOB_FUNC( null );

  B = null;
  I = BLOB_FUNC( :B );

SELECT cast(BLOB_FUNC(  'BLOB TEXT' ) ) as integer) FROM RDB$DATABASE

Unsuccessful execution caused by system error that does not preclude successful execution of subsequent statements.
feature is not supported.
BLOB and array data types are not supported for conversion operation.

SELECT cast(BLOB_FUNC(  cast( 'BLOB TEXT' as blob ) ) as integer) FROM RDB$DATABASE