实现可读流

stream.Readable 类被扩展以实现 Readable 流。

自定义 Readable 流必须调用 new stream.Readable([options]) 构造函数并实现 readable._read() 方法。

The stream.Readable class is extended to implement a Readable stream.

Custom Readable streams must call the new stream.Readable([options]) constructor and implement the readable._read() method.