Thread: Just to understand something with packet size and string

Code:

int available = Class3_Sub15.worldConnection.available();
	   if (available == 0) {
		   return false;
	   }
	   if(jString.packetType == -1) {
		   Class3_Sub15.worldConnection.read(RS2Client.inputStream.buf, 0, 1);
		   RS2Client.inputStream.pos = 0;
		   jString.packetType = RS2Client.inputStream.getUByteIsaac();
		   RS2Client.packetSize = Constants.PACKET_SIZES[jString.packetType];
		   available--;
	   }
	   if(RS2Client.packetSize == -1) {
		   if(available <= 0) {
			   return false;
		   }
		   Class3_Sub15.worldConnection.read(RS2Client.inputStream.buf, 0, 1);
		   RS2Client.packetSize = RS2Client.inputStream.buf[0] & 0xff;
		   available--;
	   }

They send packet size if the packet isn't fixed size(contains string etc).

Originally Posted by Leanbow

Code:

int available = Class3_Sub15.worldConnection.available();
	   if (available == 0) {
		   return false;
	   }
	   if(jString.packetType == -1) {
		   Class3_Sub15.worldConnection.read(RS2Client.inputStream.buf, 0, 1);
		   RS2Client.inputStream.pos = 0;
		   jString.packetType = RS2Client.inputStream.getUByteIsaac();
		   RS2Client.packetSize = Constants.PACKET_SIZES[jString.packetType];
		   available--;
	   }
	   if(RS2Client.packetSize == -1) {
		   if(available <= 0) {
			   return false;
		   }
		   Class3_Sub15.worldConnection.read(RS2Client.inputStream.buf, 0, 1);
		   RS2Client.packetSize = RS2Client.inputStream.buf[0] & 0xff;
		   available--;
	   }

They send packet size if the packet isn't fixed size(contains string etc).

So the opcode is -1?

Originally Posted by Belz

The opcode wouldn't change. If the size of the packet is -1, that means an extra byte is sent which contains the length of the packet.

But how can the packet size be -1? Wait, packet size is always being sent in the packet?

Originally Posted by JonyFX

But how can the packet size be -1? Wait, packet size is always being sent in the packet?

Client has an array with all packet sizes, if packet size is set to -1 then it asks you to define it.

Originally Posted by Leanbow

Client has an array with all packet sizes, if packet size is set to -1 then it asks you to define it.

Ah okay, i see.. But in general, what is the point of matching packet sizes ? For what purpose is this done?

Originally Posted by Whis

I think the answer I've given here should answer yours as well: [Only registered and activated users can see links. ]

The same concept is applied to game packets where strings are included. The size of the payload is set after the opcode in the packet header. This of course varies per packet.



As Leanbow has mentioned in his posts; when the client receives the packet, it decodes the header (opcode) and looks up the size of the payload of the packet in an array using the opcode. The client has a similar array to this where each element represents the size of the packet:

Code:

public static final PacketMetaDataGroup METADATA_GROUP = PacketMetaDataGroup.createFromArray(new int[] {
			-3, -3, 2, -3, -3, -3, -3, -3, 8, -3, // 0
			-3, -3, -3, 2, -3, -3, -3, -3, -3, -3, // 10
			-3, -3, -3, -3, -3, -3, -3, -3, -3, -3, // 20
			1, -3, 2, -3, -3, -3, -3, -3, -3, 6, // 30
			-3, -3, 8, -3, -3, -3, -3, 8, -3, -3, // 40
			-3, -3, -3, 8, -3, -3, -3, -3, -3, -3, // 50
			-3, 4, -3, -3, -3, -3, -1, -3, -3, -3, // 60
			-1, -3, -3, -3, 2, -3, -3, -3, -3, 0, // 70
			-3, -3, -3, -3, -3, 2, -3, 2, -3, -3, // 80
			4, 0, -3, -3, -3, -1, -3, -3, -3, -3, // 90
			-3, 8, -3, -3, 14, -3, 8, -1, -3, -3, // 100
			-3, -3, -3, -3, -3, -3, -3, -3, -3, -3, // 110
			-3, -3, -3, -3, -3, -3, -3, -3, -3, -3, // 120
			-3, -3, -3, -3, 8, -3, -3, -3, -3, -3, // 130
			8, -3, -3, -3, -3, -3, 0, -3, -3, -3, // 140
			-3, -3, -3, -3, 6, -3, -3, -3, -3, 2, // 150
			-3, 16, -3, -3, -3, -3, -3, 2, 12, -3, // 160
			6, -3, -3, -3, -3, -3, 2, -3, -3, -3, // 170
			-3, -3, -3, 4, -3, 8, -3, -3, -3, -3, // 180
			-3, 8, -3, 10, -3, -3, -3, -3, -1, -3, // 190
			-3, -3, 8, -3, -3, -3, -3, -3, -3, -3, // 200
			-3, -3, -3, 4, -3, -3, -3, -3, -3, 0, // 210
			-3, 6, -3, 2, -3, -3, -3, -3, -3, 9, // 220
			-3, 2, 14, -3, -3, -3, 8, -3, -3, -3, // 230
			-3, 8, -3, -3, -3, -3, -3, -3, -3, -1, // 240
			-3, -3, -3, -3, -3, -3,				    // 250
	});

In the code above, you can see a lot of -3. This would indicate that the packet's size has not been identified yet (The code is from the server). "-2" indicates that the size of the packet is variable and should be read as a short while "-1" indicates that the packet size must be read as a byte. Any positive value means that the size of the packet is fixed to that specific value.

After you read the size from the variable, what do you do? You just start using the packet like you do after size validation, right?

Originally Posted by JonyFX

So the opcode is -1?

varbyte, varshort is -2.