A Tour of Go - Exercise: Rot13 Reader http://tour.golang.org/#61

rot13.go

package main

import (
    "io"
    "os"
    "strings"
    //"fmt"
    "bytes"
)

var ascii_uppercase = []byte("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
var ascii_lowercase = []byte("abcdefghijklmnopqrstuvwxyz")
var ascii_uppercase_len = len(ascii_uppercase)
var ascii_lowercase_len = len(ascii_lowercase)


type rot13Reader struct {
    r io.Reader
}

func rot13(b byte) byte {
    pos := bytes.IndexByte(ascii_uppercase, b)
    if pos != -1 {
        return ascii_uppercase[(pos+13) % ascii_uppercase_len]
    }
    pos = bytes.IndexByte(ascii_lowercase, b)
    if pos != -1 {
        return ascii_lowercase[(pos+13) % ascii_lowercase_len]
    }
    return b
}

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


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

Hey, looks like almost nobody noticed that there's an exclamation mark at the end of the string :)

package main

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

type rot13Reader struct {
	r io.Reader
}

func (r13 rot13Reader) Read(p []byte) (int, error) {
	var n, err = r13.r.Read(p)

	for i := 0; i < n; i++ {
		var inp = p[i]
		if (inp >= 65 && inp <= 77) ||
			(inp >= 97 && inp <= 109) {
			p[i] = inp + 13
		} else if (inp >= 78 && inp <= 90) ||
			(inp >= 110 && inp <= 122) {
			p[i] = inp - 13
		}
	}

	return n, err
}

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