Go Tour Implementations https://tour.golang.org

infinite_a_reader.go

// https://tour.golang.org/methods/22
package main

import "golang.org/x/tour/reader"

type MyReader struct{}

func (reader MyReader) Read(b []byte) (int, error) {
	count := 0
	for i, _ := range b {
		b[i] = 'A'
		count += 1
	}

	return count, nil
}

func main() {
	reader.Validate(MyReader{})
}

rot13_reader.go

// https://tour.golang.org/methods/23
package main

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

type rot13Reader struct {
	r io.Reader
}

func (r13 rot13Reader) Read(b []byte) (int, error) {
	count, err := r13.r.Read(b)
	if err != nil {
		return count, err
	}
	for i := 0; i < count; i++ {
		b[i] = rot13(b[i])
	}
	return count, nil
}

func rot13(b byte) byte {
	switch {
	case b >= 'A' && b <= 'Z':
		return (((b - 'A') + 13) % 26) + 'A'
	case b >= 'a' && b <= 'z':
		return (((b - 'a') + 13) % 26) + 'a'
	default:
		return b
	}
}

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