object->u8vector and u8vector->object write-subu8vector and read-subu8vector on the file port
What I currently do on tcp/ip port is to first write a u8vector of size 4 representing the size of the object following and then write the u8vector representing the object.
I guess you could do the same in files. You would read 4 u8 representing the size, read-subu8vector of the size read and repeat until eof.