A Tour of Go: Exercise: rot13Reader https://tour.golang.org/methods/23

exercise-rot-reader.go

package main

import (
	"io"
	"os"
	"strings"
)

type rot13Reader struct {
	r io.Reader
}

func (r13 *rot13Reader) Read(s []byte) (int, error) {
	r := r13.r
	b := make([]byte, 1)
	for i:=0 ;; i++ {
		_, err := r.Read(b)
		if err == io.EOF {
			return i, io.EOF
		}
		c := b[0]
		var a byte
		switch {
			case 'a' <= c && c <= 'z':
				a = 'a'
			case 'A' <= c && c <= 'Z':
				a = 'A'
		}
		if a != 0 {
			c = (c - a + 13) % 26 + a
		}
		s[i] = byte(c)
	}
}

func main() {
	s := strings.NewReader("Lbh penpxrq gur pbqr!")
	r := rot13Reader{s}
	io.Copy(os.Stdout, &r)
}