I was reading http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.35 and trying to figure out how to continue a file download.
For example, suppose a file is of length 100 bytes and I have all the 100 bytes. However, I don't know what the expected file size should be, so I ask for the file and specify a Range header that looks like this:
Range: bytes=100-
Is this a valid Range request?