learngo rot13 solution

gistfile1.go

package main

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

type rot13Reader struct {
	r io.Reader
}

func (r13 *rot13Reader) Read(p []byte) (n int, err error) {
  
  n, err = r13.r.Read(p)
  
  const A = byte(65)
  const z = byte(122)
  const base = byte(96)
  
  for i := 0; i < n; i++ {
    if p[i] >= A && p[i] <= z { 
      p[i] += 13
      if p[i] > z {
        p[i] = base + ( p[i] - z )
      }
    }
  }
  
  return
}
func main() {
	s := strings.NewReader(
		"Lbh penpxrq gur pbqr!")
	r := rot13Reader{s}
	io.Copy(os.Stdout, &r)
}