Codechange: allow different limits in packet sizes

src/network/core/packet.cpp

@@ -19,6 +19,7 @@
 /**
  * Create a packet that is used to read from a network socket.
  * @param cs                The socket handler associated with the socket we are reading from.
+ * @param limit             The maximum size of packets to accept.
  * @param initial_read_size The initial amount of data to transfer from the socket into the
  *                          packet. This defaults to just the required bytes to determine the
  *                          packet's size. That default is the wanted for streams such as TCP
@@ -27,7 +28,7 @@
  *                          loose some the data of the packet, so there you pass the maximum
  *                          size for the packet you expect from the network.
  */
-Packet::Packet(NetworkSocketHandler *cs, size_t initial_read_size) : next(nullptr), pos(0)
+Packet::Packet(NetworkSocketHandler *cs, size_t limit, size_t initial_read_size) : next(nullptr), pos(0), limit(limit)
 {
 	assert(cs != nullptr);
 
@@ -37,9 +38,13 @@ Packet::Packet(NetworkSocketHandler *cs, size_t initial_read_size) : next(nullpt
 
 /**
  * Creates a packet to send
- * @param type of the packet to send
+ * @param type  The type of the packet to send
+ * @param limit The maximum number of bytes the packet may have. Default is SEND_MTU.
+ *              Be careful of compatibility with older clients/servers when changing
+ *              the limit as it might break things if the other side is not expecting
+ *              much larger packets than what they support.
  */
-Packet::Packet(PacketType type) : next(nullptr), pos(0), cs(nullptr)
+Packet::Packet(PacketType type, size_t limit) : next(nullptr), pos(0), cs(nullptr)
 {
 	/* Allocate space for the the size so we can write that in just before sending the packet. */
 	this->Send_uint16(0);
@@ -93,7 +98,7 @@ void Packet::PrepareToSend()
  */
 bool Packet::CanWriteToPacket(size_t bytes_to_write)
 {
-	return this->Size() + bytes_to_write < SEND_MTU;
+	return this->Size() + bytes_to_write < this->limit;
 }
 
 /*
@@ -191,7 +196,7 @@ void Packet::Send_string(const char *data)
  */
 size_t Packet::Send_bytes(const byte *begin, const byte *end)
 {
-	size_t amount = std::min<size_t>(end - begin, SEND_MTU - this->Size());
+	size_t amount = std::min<size_t>(end - begin, this->limit - this->Size());
 	this->buffer.insert(this->buffer.end(), begin, begin + amount);
 	return amount;
 }
@@ -260,7 +265,7 @@ bool Packet::ParsePacketSize()
 	/* If the size of the packet is less than the bytes required for the size and type of
 	 * the packet, or more than the allowed limit, then something is wrong with the packet.
 	 * In those cases the packet can generally be regarded as containing garbage data. */
-	if (size < sizeof(PacketSize) + sizeof(PacketType) || size > SEND_MTU) return false;
+	if (size < sizeof(PacketSize) + sizeof(PacketType) || size > this->limit) return false;
 
 	this->buffer.resize(size);
 	this->pos = sizeof(PacketSize);

src/network/core/packet.h

@@ -25,10 +25,11 @@ typedef uint8  PacketType; ///< Identifier for the packet
  * Internal entity of a packet. As everything is sent as a packet,
  * all network communication will need to call the functions that
  * populate the packet.
- * Every packet can be at most SEND_MTU bytes. Overflowing this
- * limit will give an assertion when sending (i.e. writing) the
- * packet. Reading past the size of the packet when receiving
- * will return all 0 values and "" in case of the string.
+ * Every packet can be at most a limited number bytes set in the
+ * constructor. Overflowing this limit will give an assertion when
+ * sending (i.e. writing) the packet. Reading past the size of the
+ * packet when receiving will return all 0 values and "" in case of
+ * the string.
  *
  * --- Points of attention ---
  *  - all > 1 byte integral values are written in little endian,
@@ -47,13 +48,15 @@ private:
 	PacketSize pos;
 	/** The buffer of this packet. */
 	std::vector<byte> buffer;
+	/** The limit for the packet size. */
+	size_t limit;
 
 	/** Socket we're associated with. */
 	NetworkSocketHandler *cs;
 
 public:
-	Packet(NetworkSocketHandler *cs, size_t initial_read_size = sizeof(PacketSize));
-	Packet(PacketType type);
+	Packet(NetworkSocketHandler *cs, size_t limit, size_t initial_read_size = sizeof(PacketSize));
+	Packet(PacketType type, size_t limit = SEND_MTU);
 
 	static void AddToQueue(Packet **queue, Packet *packet);
 	static Packet *PopFromQueue(Packet **queue);

src/network/core/tcp.cpp

@@ -126,7 +126,7 @@ Packet *NetworkTCPSocketHandler::ReceivePacket()
 	if (!this->IsConnected()) return nullptr;
 
 	if (this->packet_recv == nullptr) {
-		this->packet_recv = new Packet(this);
+		this->packet_recv = new Packet(this, SEND_MTU);
 	}
 
 	Packet *p = this->packet_recv;

src/network/core/udp.cpp

@@ -119,7 +119,8 @@ void NetworkUDPSocketHandler::ReceivePackets()
 			struct sockaddr_storage client_addr;
 			memset(&client_addr, 0, sizeof(client_addr));
 
-			Packet p(this, SEND_MTU);
+			/* The limit is SEND_MTU, but also allocate that much as we need to read the whole packet in one go. */
+			Packet p(this, SEND_MTU, SEND_MTU);
 			socklen_t client_len = sizeof(client_addr);
 
 			/* Try to receive anything */