writing twice to the same sub process golang

I have a simple scp function that is just a wrapper over the scp cli tool.

type credential struct {
	username string
	password string
	host     string
	port     string
}

func scpFile(filepath, destpath string, c *credential) error {
	cmd := exec.Command("scp", filepath, c.username+"@"+c.host+":"+destpath)

	if err := cmd.Run(); err != nil {
		return err
	}

	fmt.Println("done")
	return nil
}

This works just fine now I want to add the capability of putting in a password the SSH if scp needs it. This is what I came up with

func scpFile(filepath, destpath string, c *credential) error {
	cmd := exec.Command("scp", filepath, c.username+"@"+c.host+":"+destpath)
	stdin, err := cmd.StdinPipe()
	if err != nil {
		return err
	}
	defer stdin.Close()

	if err := cmd.Start(); err != nil {
		return err
	}

	io.WriteString(stdin, c.password+"\n")
	cmd.Wait()
	fmt.Println("done")
	return nil
}

This does not work as the password prompt just hangs there. I tried adding a 1 second sleep before I re write to stdin thinking maybe I was writing the password to fast but did not make a difference.

So I was able to find a work around by instead of trying to send the password to stdin I create a ssh session and scp a file through the ssh session. Here is the new scpFile function:

func scpFile(filePath, destinationPath string, session *ssh.Session) error {
	defer session.Close()

	f, err := os.Open(filePath)
	if err != nil {
		return err
	}
	defer f.Close()
	
	s, err := f.Stat()
	if err != nil {
		return err
	}

	go func() {
		w, _ := session.StdinPipe()
		defer w.Close()
		fmt.Fprintf(w, "C%#o %d %s\n", s.Mode().Perm(), s.Size(), path.Base(filePath))
		io.Copy(w, f)
		fmt.Fprint(w, "\x00")
	}()
	cmd := fmt.Sprintf("scp -t %s", destinationPath)
	if err := session.Run(cmd); err != nil {
		return err
	}
	return nil
}

This could probably be made better but the main idea is there