Function pointers of write_to_data_destination type are used to download object data to a network or other destination from the 5800 system server using hc_retrieve_ez. The function pointer and opaque cookie reference are supplied as arguments to hc_retrieve_ez, and the function will be called with the supplied cookie argument to deliver the downloaded data to a local data storage function.
A write_to_data_destination function should write exactly buff_len bytes to the data destination indicated by cookie, reading the bytes from the buffer at location buff. It should return a long value indicating the number of bytes actually processed. A return code that differs from buff_len indicates that the transfer should be terminated.