SendReliabilityLayer: Do not resend unreliable packets

the entire point of unreliable packets is that they don't have to be resent if they disappear. Previously to this commit, RakLib would unconditionally resend the whole datagram when nacked, wasting bandwidth.

src/generic/ResendQueueEntry.php

@@ -0,0 +1,48 @@
+<?php
+
+/*
+ * RakLib network library
+ *
+ *
+ * This project is not affiliated with Jenkins Software LLC nor RakNet.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ */
+
+declare(strict_types=1);
+
+namespace raklib\generic;
+
+use raklib\protocol\EncapsulatedPacket;
+use function microtime;
+
+final class ResendQueueEntry{
+
+	/** @var EncapsulatedPacket[] */
+	private $packets;
+	/** @var float */
+	private $timestamp;
+
+	/**
+	 * @param EncapsulatedPacket[] $packets
+	 */
+	public function __construct(array $packets){
+		$this->packets = $packets;
+		$this->timestamp = microtime(true);
+	}
+
+	/**
+	 * @return EncapsulatedPacket[]
+	 */
+	public function getPackets() : array{
+		return $this->packets;
+	}
+
+	public function getTimestamp() : float{
+		return $this->timestamp;
+	}
+}

src/generic/SendReliabilityLayer.php

@@ -26,7 +26,6 @@
 use function array_fill;
 use function assert;
 use function count;
-use function microtime;
 use function str_split;
 use function strlen;
 use function time;
@@ -67,7 +66,7 @@ final class SendReliabilityLayer{
 	/** @var Datagram[] */
 	private $packetToSend = [];
 
-	/** @var Datagram[] */
+	/** @var ResendQueueEntry[] */
 	private $recoveryQueue = [];
 
 	/** @var int[][] */
@@ -93,9 +92,17 @@ private function sendDatagram(Datagram $datagram) : void{
 			unset($this->recoveryQueue[$datagram->seqNumber]);
 		}
 		$datagram->seqNumber = $this->sendSeqNumber++;
-		$datagram->sendTime = microtime(true);
-		$this->recoveryQueue[$datagram->seqNumber] = $datagram;
 		($this->sendDatagramCallback)($datagram);
+
+		$resendable = [];
+		foreach($datagram->packets as $pk){
+			if(PacketReliability::isReliable($pk->reliability)){
+				$resendable[] = $pk;
+			}
+		}
+		if(count($resendable) !== 0){
+			$this->recoveryQueue[$datagram->seqNumber] = new ResendQueueEntry($resendable);
+		}
 	}
 
 	public function sendQueue() : void{
@@ -178,7 +185,7 @@ public function onACK(ACK $packet) : void{
 		$packet->decode();
 		foreach($packet->packets as $seq){
 			if(isset($this->recoveryQueue[$seq])){
-				foreach($this->recoveryQueue[$seq]->packets as $pk){
+				foreach($this->recoveryQueue[$seq]->getPackets() as $pk){
 					if($pk->identifierACK !== null and $pk->messageIndex !== null){
 						unset($this->needACK[$pk->identifierACK][$pk->messageIndex]);
 						if(count($this->needACK[$pk->identifierACK]) === 0){
@@ -196,7 +203,10 @@ public function onNACK(NACK $packet) : void{
 		$packet->decode();
 		foreach($packet->packets as $seq){
 			if(isset($this->recoveryQueue[$seq])){
-				$this->packetToSend[] = $this->recoveryQueue[$seq];
+				//TODO: group resends if the resulting datagram is below the MTU
+				$resend = new Datagram();
+				$resend->packets = $this->recoveryQueue[$seq]->getPackets();
+				$this->packetToSend[] = $resend;
 				unset($this->recoveryQueue[$seq]);
 			}
 		}
@@ -228,8 +238,10 @@ public function update() : void{
 		}
 
 		foreach($this->recoveryQueue as $seq => $pk){
-			if($pk->sendTime < (time() - 8)){
-				$this->packetToSend[] = $pk;
+			if($pk->getTimestamp() < (time() - 8)){
+				$resend = new Datagram();
+				$resend->packets = $pk->getPackets();
+				$this->packetToSend[] = $resend;
 				unset($this->recoveryQueue[$seq]);
 			}else{
 				break;

src/protocol/Packet.php

@@ -34,9 +34,6 @@ abstract class Packet extends BinaryStream{
 	/** @var int */
 	public static $ID = -1;
 
-	/** @var float|null */
-	public $sendTime;
-
 	/**
 	 * @return string
 	 * @throws BinaryDataException