Function with_file_reader 

pub fn with_file_reader<S, T>(
    source: &mut S,
    entry: &FileEntry,
    consume: impl FnOnce(&mut dyn Read) -> Result<T, FilesystemError>,
) -> Result<T, FilesystemError>
where
    S: Filesystem + Send + ?Sized,

Run consume over a reader that streams entry’s bytes out of source.