Function untrusted::read_all_optional

pub fn read_all_optional<F, R, E>(
    input: Option<Input>, 
    incomplete_read: E, 
    read: F
) -> Result<R, E> where
    F: FnOnce(Option<&mut Reader>) -> Result<R, E>, 

Calls read with the given input as a Reader, ensuring that read consumed the entire input. When input is None, read will be called with None.