解答

1. use std::io::Read;

3. struct RotDecoder<R: Read> {
4. input: R,
5. rot: u8,
6. }

8. impl<R: Read> Read for RotDecoder<R> {
9. fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
10. let size = self.input.read(buf)?;
11. for b in &mut buf[..size] {
12. if b.is_ascii_alphabetic() {
13. let base = if b.is_ascii_uppercase() { 'A' } else { 'a' } as u8;
14. *b = (*b - base + self.rot) % 26 + base;
15. }
16. }
17. Ok(size)
18. }
19. }

21. fn main() {
22. let mut rot =
23. RotDecoder { input: "Gb trg gb gur bgure fvqr!".as_bytes(), rot: 13 };
24. let mut result = String::new();
25. rot.read_to_string(&mut result).unwrap();
26. println!("{}", result);
27. }

29. #[cfg(test)]
30. mod test {
31. use super::*;

33. #[test]
34. fn joke() {
35. let mut rot =
36. RotDecoder { input: "Gb trg gb gur bgure fvqr!".as_bytes(), rot: 13 };
37. let mut result = String::new();
38. rot.read_to_string(&mut result).unwrap();
39. assert_eq!(&result, "To get to the other side!");
40. }

42. #[test]
43. fn binary() {
44. let input: Vec<u8> = (0..=255u8).collect();
45. let mut rot = RotDecoder::<&[u8]> { input: input.as_ref(), rot: 13 };
46. let mut buf = [0u8; 256];
47. assert_eq!(rot.read(&mut buf).unwrap(), 256);
48. for i in 0..=255 {
49. if input[i] != buf[i] {
50. assert!(input[i].is_ascii_alphabetic());
51. assert!(buf[i].is_ascii_alphabetic());
52. }
53. }
54. }
55. }