AFAIK, that should be used to download the whole file again, if the modification time of the file in the server is newer than the whole file I've previously downloaded.

What I have is about 40MB of a 45MB binary file from a interrupted connection, and I want to resume in a new one, skipping that range of bytes...

I´m just looking for a standard way to do this, and not to write code from scratch using lower level methods.