rot13.go

package main

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

type rot13Reader struct {
	r io.Reader
}

var rot13_upper = []byte("NOPQRSTUVWXYZABCDEFGHIJKLM")
var rot13_lower = []byte("nopqrstuvwxyzabcdefghijklm")

func (rot *rot13Reader) Read(b []byte) (int, error) {
	n, err := rot.r.Read(b)
	if err != nil {
		return 0, err
	}
	for i := range b {
		if 'a' <= b[i] && b[i] <= 'z' {
			b[i] = rot13_lower[b[i]-'a']
		} else if 'A' <= b[i] && b[i] <= 'Z' {
			b[i] = rot13_upper[b[i]-'A']
		}
	}
	return n, nil
}

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