Function untrusted::read_all_optional

pub fn read_all_optional<'a, F, R, E>(input: Option<Input<'a>>,
                                      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.