Cache question. Help needed !!!

Hi,
 
I want to use libwww for downloading files from web servers.
I’m using the output stream as in the ComLine example – writing to a
file and
I’d like to use the persistent cache.
My question is, if the file for the given URI is already in the cache
and is valid,
how NOT to save the result in the additional file (the output stream).
 
As it works now – first time the URI is saved in the file & the cache,
the 
second time, as I understand,  it’s copied from the cache to the file
specified in the output stream … How to force libwww from copying the
file second time ?
 
Thanks in advance,
Gregory