NetworkSession: add support for discarding repeated packets before they're decoded

this dramatically reduces the server workload dealing with spammy packets like right-click interactions trigger.
It also solves the problem of players getting kicked for right-clicking for too long.

src/network/mcpe/NetworkSession.php

@@ -58,6 +58,7 @@ use pocketmine\network\mcpe\protocol\ChunkRadiusUpdatedPacket;
 use pocketmine\network\mcpe\protocol\ClientboundCloseFormPacket;
 use pocketmine\network\mcpe\protocol\ClientboundPacket;
 use pocketmine\network\mcpe\protocol\DisconnectPacket;
+use pocketmine\network\mcpe\protocol\InventoryTransactionPacket;
 use pocketmine\network\mcpe\protocol\ModalFormRequestPacket;
 use pocketmine\network\mcpe\protocol\MovePlayerPacket;
 use pocketmine\network\mcpe\protocol\NetworkChunkPublisherUpdatePacket;
@@ -109,6 +110,7 @@ use pocketmine\promise\PromiseResolver;
 use pocketmine\Server;
 use pocketmine\timings\Timings;
 use pocketmine\utils\AssumptionFailedError;
+use pocketmine\utils\Binary;
 use pocketmine\utils\BinaryDataException;
 use pocketmine\utils\BinaryStream;
 use pocketmine\utils\ObjectSet;
@@ -194,6 +196,17 @@ class NetworkSession{
 	 */
 	private ObjectSet $disposeHooks;
 
+	/**
+	 * @var string[]
+	 * @phpstan-var array<int, string>
+	 */
+	private array $repeatedPacketFilters = [];
+	/**
+	 * @var int[]
+	 * @phpstan-var array<int, int>
+	 */
+	private array $repeatedPacketFilterStats = [];
+
 	public function __construct(
 		private Server $server,
 		private NetworkSessionManager $manager,
@@ -221,6 +234,8 @@ class NetworkSession{
 			$this->onSessionStartSuccess(...)
 		));
 
+		$this->addRepeatedPacketFilter(InventoryTransactionPacket::NETWORK_ID);
+
 		$this->manager->add($this);
 		$this->logger->info($this->server->getLanguage()->translate(KnownTranslationFactory::pocketmine_network_session_open()));
 	}
@@ -350,6 +365,44 @@ class NetworkSession{
 		}
 	}
 
+	public function addRepeatedPacketFilter(int $packetId) : void{
+		$this->repeatedPacketFilters[$packetId] = "";
+		$this->repeatedPacketFilterStats[$packetId] = 0;
+	}
+
+	public function removeRepeatedPacketFilter(int $packetId) : void{
+		unset($this->repeatedPacketFilters[$packetId]);
+		unset($this->repeatedPacketFilterStats[$packetId]);
+	}
+
+	/**
+	 * Returns the stats for repeated packet filters, indexed by packet ID.
+	 * The value is the number of times a packet was dropped due to being repeated.
+	 *
+	 * @return int[]
+	 * @phpstan-return array<int, int>
+	 */
+	public function getRepeatedPacketFilterStats() : array{
+		return $this->repeatedPacketFilterStats;
+	}
+
+	private function checkRepeatedPacketFilter(string $buffer) : bool{
+		//TODO: would be great if we didn't repeat reading the ID inside PacketPool
+		$dummy = 0;
+		$packetId = Binary::readUnsignedVarInt($buffer, $dummy);
+
+		if(isset($this->repeatedPacketFilters[$packetId])){
+			if($buffer === $this->repeatedPacketFilters[$packetId]){
+				$this->repeatedPacketFilterStats[$packetId]++;
+				return true;
+			}
+
+			$this->repeatedPacketFilters[$packetId] = $buffer;
+		}
+
+		return false;
+	}
+
 	/**
 	 * @throws PacketHandlingException
 	 */
@@ -403,6 +456,10 @@ class NetworkSession{
 			try{
 				$stream = new BinaryStream($decompressed);
 				foreach(PacketBatch::decodeRaw($stream) as $buffer){
+					if($this->checkRepeatedPacketFilter($buffer)){
+						continue;
+					}
+
 					$this->gamePacketLimiter->decrement();
 					$packet = $this->packetPool->getPacket($buffer);
 					if($packet === null){