excercise-rot-reader.go

package main

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

type rot13Reader struct {
	r io.Reader
}

func (r *rot13Reader) Read(b []byte) (int, error) {
	l, e := r.r.Read(b)
	for i, c := range b {
		if c == ' ' || c == '!' {
			continue
		}

		if ('a' <= c && c <= 'm') || ('A' <= c && c <= 'M') {
			b[i] = c + 13
		} else {
			b[i] = c - 13
		}
	}
	return l, e
}

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