The-Golang-Standard-Library-by-Example

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        sr := strings.NewReader("ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890")
	buf := bufio.NewReaderSize(sr, 0) 
	b := make([]byte, 10)
	fmt.Println(buf.Buffered()) // 
	s, _ := buf.Peek(5)
	s[0], s[1], s[2] = 'a', 'b', 'c'
	fmt.Printf("%d   %q\n", buf.Buffered(), s) 

为啥使用了Peek 后 buf.Buffered()就不是0了。

因为Peek操作 会导致fill strings.NewReader的数据到bufio的buf中