Session: Prevent bogus pongs from reaching the event listener

this should never normally happen, but if the pong has a timestamp in the future, we'll end up reporting a negative ping to the event listener.

Author: dktapps

src/server/Session.php

@@ -263,8 +263,13 @@ private function handleEncapsulatedPacketRoute(EncapsulatedPacket $packet) : voi
 	 * @param int $sendPongTime TODO: clock differential stuff
 	 */
 	private function handlePong(int $sendPingTime, int $sendPongTime) : void{
-		$this->lastPingMeasure = $this->server->getRakNetTimeMS() - $sendPingTime;
-		$this->server->getEventListener()->onPingMeasure($this->internalId, $this->lastPingMeasure);
+		$currentTime = $this->server->getRakNetTimeMS();
+		if($currentTime < $sendPingTime){
+			$this->logger->debug("Received invalid pong: timestamp is in the future by " . ($sendPingTime - $currentTime) . " ms");
+		}else{
+			$this->lastPingMeasure = $currentTime - $sendPingTime;
+			$this->server->getEventListener()->onPingMeasure($this->internalId, $this->lastPingMeasure);
+		}
 	}
 
 	public function handlePacket(Packet $packet) : void{