Function eof 

pub fn eof<I, E>(input: I) -> Result<(I, I), Err<E>>
where
    I: InputLength + Clone,
    E: ParseError<I>,

Available on crate feature crypto only.

returns its input if it is at the end of input data

When we’re at the end of the data, this combinator will succeed

let parser = eof;
assert_eq!(parser("abc"), Err(Err::Error(("abc", ErrorKind::Eof))));
assert_eq!(parser(""), Ok(("", "")));