go程序io过程中报错EOF是什么东西

func main() {
	r := strings.NewReader("Hello, Reader!")

	b := make([]byte, 8)
	for {
		n, err := r.Read(b)
		fmt.Printf("n = %v err = %v b = %v\n", n, err, b)
		fmt.Printf("b[:n] = %q\n", b[:n])
		//fmt.Print(err)
		if err!=nil{
			fmt.Println("错误是:",err)
			break
		}
	}
}

运行结果

n = 8 err = <nil> b = [72 101 108 108 111 44 32 82]
b[:n] = "Hello, R"
n = 6 err = <nil> b = [101 97 100 101 114 33 32 82]
b[:n] = "eader!"
n = 0 err = EOF b = [101 97 100 101 114 33 32 82]
b[:n] = ""
错误是: EOF