close_sdtin.go

package main

import (
	"fmt"
	"io"
	"os"
	"syscall"
)

func main() {
	for i := 0; i<3; i++ {
		oldStdin, _ := syscall.Dup(syscall.Stdin)

		go func(dst io.Writer, src io.Reader) error {
			var err error
			buf := make([]byte, 32*1024)
			for {
				fmt.Print("prepare to read\n")
				nr, er := src.Read(buf)
				fmt.Printf("read done: %d bytes\n", nr)
				if nr > 0 {
					fmt.Print("prepare to write\n")
					nw, ew := dst.Write(buf[0:nr])
					fmt.Printf("write done: %d bytes\n", nw)
					if ew != nil {
						fmt.Print("interrupt ew != nil\n")
						err = ew
						break
					}
					if nr != nw {
						fmt.Print("interrupt nr != nw\n")
						err = io.ErrShortWrite
						break
					}
				}
				if er == io.EOF {
					fmt.Print("interrupt EOF\n")
					break
				}
				if er != nil {
					fmt.Print("interrupt er != nil\n")
					err = er
					break
				}
			}
			fmt.Print("Copy finished\n")
			return err
		}(os.Stdout, os.Stdin)

		fmt.Print("Closing stdin\n")
		os.Stdin.Close()
		fmt.Print("Closed stdin\n")

		syscall.Dup2(oldStdin, syscall.Stdin)

		syscall.Close(oldStdin)

		os.Stdin = os.NewFile(uintptr(syscall.Stdin), "/dev/stdin")

		var ans string
		fmt.Fprint(os.Stderr, "Scanning:\n")
		_, err := fmt.Scanf("%s\n", &ans)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Failed to scan: %#v\n",err.Error())
		} else {
			fmt.Fprintf(os.Stderr, "ans: \"%s\"\n",ans)
		}
	}
}