下载最大文件只能2G超过后buffer存不下会下载失败

[CZDonald]

The value of "length" is out of range. It must be >= 0 && <= 2147483647. Received 3567234573

[guoyunhe]

我做了一个不用一口气塞满 buffer 的包，内存占用很小 https://github.com/guoyunhe/downloader