Go 语言教程中的一个示例,用的装饰模式,实现了 Linux 的 cat 功能,还有一个 rot13 选项,可以对字符串进行简单加密。
实现了 reader 接口的 File 对象。
file.go
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package file
import (
"os"
"syscall"
)
type File struct {
fd int // file descriptor number
name string // file name at Open time
}
func newFile(fd int, name string) *File {
if fd < 0 {
return nil
}
return &File{fd, name}
}
var (
Stdin = newFile(0, "/dev/stdin")
Stdout = newFile(1, "/dev/stdout")
Stderr = newFile(2, "/dev/stderr")
)
func Open(name string, mode int, perm int) (file *File, err os.Error) {
r, e := syscall.Open(name, mode, perm)
if e != 0 {
err = os.Errno(e)
}
return newFile(r, name), err
}
func (file *File) Close() os.Error {
if file == nil {
return os.EINVAL
}
e := syscall.Close(file.fd)
file.fd = -1 // so it can't be closed again
if e != 0 {
return os.Errno(e)
}
return nil
}
func (file *File) Read(b []byte) (ret int, err os.Error) {
if file == nil {
return -1, os.EINVAL
}
r, e := syscall.Read(file.fd, b)
if e != 0 {
err = os.Errno(e)
}
return int(r), err
}
func (file *File) Write(b []byte) (ret int, err os.Error) {
if file == nil {
return -1, os.EINVAL
}
r, e := syscall.Write(file.fd, b)
if e != 0 {
err = os.Errno(e)
}
return int(r), err
}
func (file *File) String() string {
return file.name
}
reader 接口及装饰后的对象 rotate13,
cat_rot13.go
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"./file"
"flag"
"fmt"
"os"
)
var rot13Flag = flag.Bool("rot13", false, "rot13 the input")
func rot13(b byte) byte {
if 'a' <= b && b <= 'z' {
b = 'a' + ((b - 'a') + 13) % 26
}
if 'A' <= b && b <= 'Z' {
b = 'A' + ((b - 'A') + 13) % 26
}
return b
}
type reader interface {
Read(b []byte) (ret int, err os.Error)
String() string
}
type rotate13 struct {
source reader
}
func newRotate13(source reader) *rotate13 {
return &rotate13{source}
}
func (r13 *rotate13) Read(b []byte) (ret int, err os.Error) {
r, e := r13.source.Read(b)
for i := 0; i < r; i++ {
b[i] = rot13(b[i])
}
return r, e
}
func (r13 *rotate13) String() string {
return r13.source.String()
}
// end of rotate13 implementation
func cat(r reader) {
const NBUF = 512
var buf [NBUF]byte
if *rot13Flag {
r = newRotate13(r) // 用 rotate13 装饰 r,使得所有输出自动改变。
}
for {
switch nr, er := r.Read(&buf); {
case nr < 0:
fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", r.String(), er.String())
os.Exit(1)
case nr == 0: // EOF
return
case nr > 0:
nw, ew := file.Stdout.Write(buf[0:nr])
if nw != nr {
fmt.Fprintf(os.Stderr, "cat: error writing from %s: %s\n", r.String(), ew.String())
}
}
}
}
func main() {
flag.Parse() // Scans the arg list and sets up flags
if flag.NArg() == 0 {
cat(file.Stdin)
}
for i := 0; i < flag.NArg(); i++ {
f, err := file.Open(flag.Arg(i), 0, 0)
if f == nil {
fmt.Fprintf(os.Stderr, "cat: can't open %s: error %s\n", flag.Arg(i), err)
os.Exit(1)
}
cat(f)
f.Close()
}
}
有点长,但是用得很恰当,呵呵