My solution to "rot13Reader" excercise of "A Tour of Go"

rot13Reader.go

package main

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

type rot13Reader struct {
	r io.Reader
}

func (rot *rot13Reader) Read(b []byte) (int, error) {
	n, err := rot.r.Read(b)
	
	for i := 0; i < n; i++ {
		b[i] = rot13(b[i])
	}

	return n, err
}

func rot13(c byte) byte {
	var offset int
	switch {
	case c <= 'Z' && c >= 'A':
		offset = int('A')
	case c <= 'z' && c >= 'a':
		offset = int('a')
	default:
		return c
	}
	return byte(offset + (int(c)-offset+13)%26)
}

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