outgoingMessage.writableEnded
如果调用了 outgoingMessage.end()，则为 true。该属性不表示数据是否被刷新。为此目的，则改用 message.writableFinished。
¥Is true if outgoingMessage.end() has been called. This property does
not indicate whether the data has been flushed. For that purpose, use
message.writableFinished instead.