golang IO COPY

使用golang实现 IO copy,测试程序如下:

package main
import (
	"fmt"
	"io"
	"os"
	"syscall"
)
func main() {
	var errCh chan error
	errCh = Go(func() error {
		return test_stdout()
	})
	if err := <-errCh; err != nil {
		fmt.Printf("End io_copy: %s\n", err)
		//return err
	}
}
//异步执行
func Go(f func() error) chan error {
	ch := make(chan error, 1)
	go func() {
		ch <- f()
	}()
	return ch
}
//输入流复制到文件里面
func test_stdin() error {
	var out io.Writer
	var in io.Reader
	in = os.NewFile(uintptr(syscall.Stdin), "/dev/stdin")
	out, _ = os.OpenFile("D:/golang/project/docker/env.txt", os.O_RDWR, 0666)
	n, err := io.Copy(out, in)
	fmt.Printf("\n write %d err %v \n", n, err)
	return err
}
//文件里面复制到输出流
func test_stdout() error {
	var out io.Writer
	var in io.Reader
	out = os.NewFile(uintptr(syscall.Stdout), "/dev/stdout")
	in, _ = os.OpenFile("D:/golang/project/docker/env.txt", os.O_RDWR, 0666)
	n, err := io.Copy(out, in)
	fmt.Printf("\n write %d err %v \n", n, err)
	return err
}

再看看io.Copy的代码:

func Copy(dst Writer, src Reader) (written int64, err error) {
	// If the reader has a WriteTo method, use it to do the copy.
	// Avoids an allocation and a copy.
	if wt, ok := src.(WriterTo); ok {
		return wt.WriteTo(dst)
	}
	// Similarly, if the writer has a ReadFrom method, use it to do the copy.
	if rt, ok := dst.(ReaderFrom); ok {
		return rt.ReadFrom(src)
	}
	buf := make([]byte, 32*1024)
	for {
		nr, er := src.Read(buf)
		if nr > 0 {
			nw, ew := dst.Write(buf[0:nr])
			if nw > 0 {
				written += int64(nw)
			}
			if ew != nil {
				err = ew
				break
			}
			if nr != nw {
				err = ErrShortWrite
				break
			}
		}
		if er == EOF {
			break
		}
		if er != nil {
			err = er
			break
		}
	}
	return written, err
}

阻塞式的从src输入流读数据到dst输出流

本文来自:开源中国博客

感谢作者:golang_yh

查看原文:golang IO COPY

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