Function readfilez::read_part_from_file

pub fn read_part_from_file(
    fh: &mut File, 
    offset: u64, 
    len: LengthSpec
) -> Result<FileHandle>

Reads a part of the file contents, use this if the file is too big and needs to be read in parts, starting at offset and until the given LengthSpec is met. if you want a more ergonomic interface, use ContinuableFile or ChunkedFile. fh is a reference because this function is intended to be called multiple times