rot13Reader.go

// solution to rot13Reader exercise in golang tour

package main

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

type rot13Reader struct {
	r io.Reader
}

func (r rot13Reader) Read(p []byte) (int, error) {
	n, err := r.r.Read(p)
	for i := 0; i < n; i++ {
		p[i] = rot13(p[i])
	}
	
	if err == io.EOF {
		return n, err
	}

	return n, nil
}

// takes byte, validates ASCII alpha char, returns rot-13-encoded char (as byte)
func rot13(b byte) byte {
	upperBound := byte('z')
	
	// set proper upper bound
	if b >= byte('a') && b <= byte('z') { // lowercase
		// do nothing, upper bound is lowercase by default
	} else if b >= byte('A') && b <= byte('Z') { // uppercase
		// set upperBound to uppercase
		upperBound = byte('Z')
	} else {
		// not ASCII alpha char, just return byte as is
		return b
	}
	
	// rot 13 encode
	b += 13
	if b > upperBound {
		b -= 26
	}
	
	return b
}

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