Exercise: Rot13 Reader

A common pattern is an io.Reader that wraps another io.Reader, modifying the stream in some way.

For example, the gzip.NewReader function takes an io.Reader (a stream of gzipped data) and returns a *gzip.Reader that also implements io.Reader (a stream of the decompressed data).

Implement a rot13Reader that implements io.Reader and reads from anio.Reader, modifying the stream by applying the ROT13 substitution cipher to all alphabetical characters.

The rot13Reader type is provided for you. Make it an io.Reader by implementing its Read method

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 - 'A' + 'N'
	case p >= 'N' && p <= 'Z': p = p - 'N' + 'A'
	case p >= 'a' && p <= 'm': p = p - 'a' + 'n'
	case p >= 'n' && p <= 'z': p = p - 'n' + 'a'
	}
	
	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(
		"Lbh penpxrq gur pbqr!")
	r := rot13Reader{s}
	io.Copy(os.Stdout, &r)
}