Function state_iterator_key_read 

pub unsafe extern "C" fn state_iterator_key_read(
    iterator: u64,
    start: *mut u8,
    length: u32,
    offset: u32,
) -> u32

Read a section of the key the iterator is currently pointing at. Returns either

• u32::MAX if the iterator has already been deleted
• the amount of data that was copied. This will never be more than the supplied length. Before the first call to the state_iterator_next function this returns (sections of) the key that was used to create the iterator. After state_iterator_next returns (the encoding of) None this method returns (sections of) the key at the first node returned by the iterator.