Interfaces and structs

s.go

package main

import (
	"errors"
	"io"
	"os"
	"strings"
	"unicode"
)

const maxBufferSize = 512 * 1024

func readString(r io.Reader) (string, error) {
	buffer := make([]byte, 0)
	one := []byte{0}
	for n, err := r.Read(one); n > 0 && err == nil; n, err = r.Read(one) {
		if one[0] == '\n' {
			return string(buffer), nil
		} else {
			buffer = append(buffer, one[0])
		}
		if len(buffer) > maxBufferSize {
			return string(buffer), errors.New("too_big_string")
		}
	}
	return "", errors.New("Can't find \\n")
}

type AReader struct {
}

func (a *AReader) Read(b []byte) (int, error) {
	for k := range b {
		b[k] = 'A'
	}
	return len(b), nil
}

type rot13Reader struct {
	r io.Reader
}

func (rot *rot13Reader) Read(b []byte) (int, error) {
	n, err := rot.r.Read(b)
	for k := range b {
		if unicode.IsLetter(rune(b[k])) {
			start := 'a'
			if b[k] >= 'A' && b[k] <= 'Z' {
				start = 'A'
			}
			pos := (b[k] - byte(start) + 13) % 26
			b[k] = byte(start) + pos
		}
	}
	return n, err
}

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

}