A Tour of Go - [Exercise : Rot13 Reader](http://tour.golang.org/#61) & [연습: Rot13 Reader](https://go-tour-kr.appspot.com/#61)

rot13.go

package main

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

type rot13Reader struct {
	r io.Reader
}

func (rot rot13Reader) Read(p []byte) (int, error) {
	n, err := rot.r.Read(p)
	for i, v := range p {
		p[i] = rot13(v)
	}

	return n, err
}

func rot13(c byte) byte {
	if (c >= 'a' && c < 'n') || (c >= 'A' && c < 'N') {
		c = c + 13
	} else if (c >= 'n' && c <= 'z') || (c >= 'N' && c <= 'Z') {
		c = c - 13
	}

	return c
}

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