A Tour of Go: Exercise: Rot13 Reader

package main  
  
import (  
    "io"  
    "os"  
    "strings"  
)  
  
type rot13Reader struct {  
    r io.Reader  
}  
  
func rot13(p byte) byte {  
    switch {  
    case p >= 'A' && p <= 'M': p = p + 13  
    case p >= 'N' && p <= 'Z': p = p - 13  
    case p >= 'a' && p <= 'm': p = p + 13  
    case p >= 'n' && p <= 'z': p = p - 13  
    }  
      
    return p  
}  
  
  
func (v rot13Reader)  Read(p []byte) (n int, err error) {  
    original := make([]byte, 50)  
    i, err := v.r.Read(original)  
    for index, value := range original[:i] {  
        p[index] = rot13(value)  
    }  
    return i, err  
}  
  
func main() {  
    s := strings.NewReader(  
        "purakha")  
    r := rot13Reader{s}  
    io.Copy(os.Stdout, &r)  
}