Control of amount of data read

I am trying to find a way to specify  the amount of data read from an
http or ftp file. I have been reading through the library documentation
and examples, and I couldn't find any. Does any body know fo a way to do


Rabih Zbib
Visiting Student
Center for Educational Computing Initiatives
One Amherst Street, MIT Bldg E40-370
Cambridge, MA 02139