rot13 from the Go tour

rot13.go

package main

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

type rot13Reader struct {
	r io.Reader
}

func (r rot13Reader) Read(d []byte) (int, error) {
	count, err := r.r.Read(d)
	if err != nil {
		return 0, err	
	}
	for i := 0; i < count; i++ {
		code := uint(d[i])
		if code >= 65 && code <= 90 {
			code = ((code - 65) + 13 ) % (90 - 65 + 1) + 65
		} else if code >= 97 && code <= 122 {
			code = ((code - 97) + 13 ) % (122 - 97 + 1) + 97
		} 
		d[i] = byte(code)
	}
	return count, nil
}

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