java websocket中的ping-pong 機制

時間 2019-12-14

標籤 java websocket ping pong 機制欄目 Java 简体版

原文原文鏈接

參考源碼：java

https://github.com/TooTallNate/Java-WebSocket/blob/master/src/main/java/org/java_websocket/client/WebSocketClient.javagit

https://github.com/TooTallNate/Java-WebSocket/blob/master/src/main/java/org/java_websocket/AbstractWebSocket.javagithub

https://github.com/TooTallNate/Java-WebSocket/blob/master/src/main/java/org/java_websocket/WebSocket.javaweb

https://github.com/TooTallNate/Java-WebSocket/blob/master/src/main/java/org/java_websocket/WebSocketImpl.javawebsocket

https://github.com/TooTallNate/Java-WebSocket/blob/master/src/main/java/org/java_websocket/drafts/Draft_6455.java網絡

文章參考：socket

https://blog.csdn.net/u010770993/article/details/70312279

http://www.javashuo.com/article/p-giacuwnn-cb.html

機制圖解：

注：websocket基於tcp協議，它在第一次鏈接時發起http請求，以後創建握手tcp

在websocket中設置setConnectionLostTimeout參數，解釋爲：Setter for the interval checking for lost connections，意思是間隔檢查鏈接是否丟失this

總體是調用順序爲：onWebsocketOpen -》 startConnectionLostTimer -》 restartConnectionLostTimer-》 scheduleAtFixedRate -》 executeConnectionLostDetectionspa

關鍵代碼

this.connectionLostTimeout = TimeUnit.SECONDS.toNanos(connectionLostTimeout);
if (this.connectionLostTimeout <= 0) {
　　log.trace("Connection lost timer stopped");
   cancelConnectionLostTimer();
   return;
}

long minimumPongTime = (long) (System.nanoTime() - ( connectionLostTimeout * 1.5 ));
for( WebSocket conn : connections ) {
　　executeConnectionLostDetection(conn, minimumPongTime);
}

WebSocketImpl webSocketImpl = (WebSocketImpl) webSocket;
if( webSocketImpl.getLastPong() < minimumPongTime ) {
　　log.trace("Closing connection due to no pong received: {}", webSocketImpl);
　　webSocketImpl.closeConnection( CloseFrame.ABNORMAL_CLOSE, "The connection was closed because the other endpoint did not respond with a pong in time. For more information check: https://github.com/TooTallNate/Java-WebSocket/wiki/Lost-connection-detection" );
} else {
　　if( webSocketImpl.isOpen() ) {
　　　　webSocketImpl.sendPing();
　　} else {
　　　　log.trace("Trying to ping a non open connection: {}", webSocketImpl);
　　}
}

connectionLostTimeout在設置後會轉爲納秒時間， minimumPongTime爲當前納秒時間減去connectionLostTimeout的1.5倍，當最後一次Pong的時間小於minimumPongTime時產生close，即在間隔時間內未收到Pong響應關閉鏈接。若是正常則繼續發送ping，即調用sendPing。

在服務端收到ping的時候，當即下發pong，二者的容忍時間爲connectionLostTimeout是1.5倍，即設十秒的話就是容忍十五秒。當網絡發生異常時，二者狀況，服務端沒有收到ping亦或者客戶端沒有收到pong，觸發close。