A Tour of Go: Exercise: Rot13 Reader

A Tour of Go

Exercise: Rot13 Reader

A common pattern is anio.Readerthat wraps anotherio.Reader, modifying the stream in some way.

For example, thegzip.NewReaderfunction takes anio.Reader(a stream of gzipped data) and returns a*gzip.Readerthat also implementsio.Reader(a stream of the decompressed data).

Implement arot13Readerthat implementsio.Readerand reads from anio.Reader, modifying the stream by applying theROT13substitution cipher to all alphabetical characters.

Therot13Readertype is provided for you. Make it anio.Readerby implementing itsReadmethod

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)
}