keep-alive

基本解释

In order to maintain presence, the chat application can send keep-alive messages on the websocket to prevent it being closed due to an idle timeout.
爲了保持存在的狀態，聊天應用要發送“連接保持（Keep Alive）”的消息給WebSocket，來避免該連接因爲閑置超時而關閉。
Since clients do not wish to be forcefully disconnected, they will automatically send a keep-alive message if the connection is inactive for the number of seconds specified by this parameter.
由於客戶機不希望強制斷開連接，因此，儅連接閑置的時間爲此蓡數指定的秒數時，客戶機將自動發送 keep-alive 消息。
Persistent connections specify that an outgoing HTTP response should use a persistent (keep-alive) connection instead of a connection that closes after one request or response exchange occurs.
持久連接指定傳出的 HTTP 響應應該使用持久（保持活動狀態）連接，而不是在請求或響應交換後關閉的連接。

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