rot13Reader.go

// rot13Reader's `Read([]byte) (int, error)` implementation
// following the go tool tour
// mtso, 2016
// would be interesting to try a ternary with: 
// https://play.golang.org/p/ZgLwC_DHm0

package main

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

type rot13Reader struct {
	r io.Reader
}

func (r13 rot13Reader) Read(b []byte) (l int, e error) {
	// pass the byte slice into the reader value
	l, e = r13.r.Read(b)
	// ROT13 on the characters in the buffer
	for i := 0; i < l; i++ {
		// temp var c
		c := b[i]
		// if the byte is a space, skip
		if c == 32 {
			continue
		}
		// If A-Z, limit is 90 (Z)
		limit := byte(90)
		// c is greater than 90,
		// c is lowercase a-z, where z is 122
		if c > limit {
			limit = 122
		}
		// Shift the byte by 13 positions
		b[i] += 13
		// If the byte is greater than Z or z
		// shift the byte back 26 positions
		if b[i] > limit {
			b[i] -= 26
		}
	}
	return
}

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