Go标准库-io-multi ""
//接受多个Reader/Writer
//返回一个Reader/Writer
//操作这个Reader/Writer 就相当于操作多个Reader/Writer
func MultiReader(readers ...Reader) Reader {
return &multiReader{readers}
}
func MultiWriter(writers ...Writer) Writer {
return &multiWriter{writers}
}
multi中定义了两个内部struct，multiReader 和 multiWriter 分别实现了 io.Reader 和 io.Writer
type multiReader struct {
readers []Reader
}
type multiWriter struct {
writers []Writer
}
func (mr *multiReader) Read(p []byte) (n int, err error) {
for len(mr.readers) > 0 {
n, err = mr.readers[0].Read(p)
if n > 0 || err != EOF {
if err == EOF {
// Don't return EOF yet. There may be more bytes
// in the remaining readers.
err = nil
}
return
}
mr.readers = mr.readers[1:]
}
return 0, EOF
}
func (t *multiWriter) Write(p []byte) (n int, err error) {
for _, w := range t.writers {
n, err = w.Write(p)
if err != nil {
return
}
if n != len(p) {
err = ErrShortWrite
return
}
}
return len(p), nil
}
我们举两个例子，来谈谈应用。
MultiReader:
readers := []io.Reader{
strings.NewReader("from strings reader"),
bytes.NewBufferString("from bytes buffer"),
}
reader := io.MultiReader(readers...)
data := make([]byte, 0, 1024)
var (
err error
n int
)
for err != io.EOF {
tmp := make([]byte, 512)
n, err = reader.Read(tmp)
if err == nil {
data = append(data, tmp[:n]...)
} else {
if err != io.EOF {
panic(err)
}
}
}
fmt.Printf("%s\n", data)
输出
from strings readerfrom bytes buffer
MultiReader只是逻辑上将多个Reader组合起来，并不能通过调用一次Read方法获取所有Reader的内容。在所有的Reader内容都被读完后，Reader会返回EOF。
MultiWriter：
file, err := os.Create("tmp.txt")
if err != nil {
panic(err)
}
defer file.Close()
writers := []io.Writer{
file,
os.Stdout,
}
writer := io.MultiWriter(writers...)
writer.Write([]byte("MultiWriter test"))
这段程序执行后在生成tmp.txt文件，同时在文件和屏幕中都输出：MultiWriter test 这和Unix中的tee命令类似。
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