A common pattern is an io.Reader that wraps another io.Reader,
modifying the stream in some way.
For example, the gzip.NewReader function takes an io.Reader (a
stream of gzipped data) and returns a *gzip.Reader that also implements io.Reader (a stream of
the decompressed data).
Implement a rot13Reader that implements io.Reader and
reads from an io.Reader, modifying the stream by applying the ROT13substitution cipher to all alphabetical characters.
The rot13Reader type is provided for you. Make it an io.Reader by
implementing its Read method.
加密方法：凱撒加密，key爲13
package main
import (
"io"
"os"
"strings"
)
type rot13Reader struct {
r io.Reader
}
func Rot13(b byte) byte {
switch {
case 'A' <= b && b <= 'M':
b = b + 13
case 'M' < b && b <= 'Z':
b = b - 13
case 'a' <= b && b <= 'm':
b = b + 13
case 'm' < b && b <= 'z':
b = b - 13
}
return b
}
func (read *rot13Reader) Read(p []byte) (n int, err error){
n, err = read.r.Read(p)
for i, value := range p {
p[i] = Rot13(value)
}
return
}
func main() {
s := strings.NewReader(
"Lbh penpxrq gur pbqr!")
r := rot13Reader{s}
io.Copy(os.Stdout, &r)
}