BasePacket.java

package emu.grasscutter.net.packet;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

import com.google.protobuf.GeneratedMessageV3;
import emu.grasscutter.net.proto.PacketHeadOuterClass.PacketHead;
import emu.grasscutter.utils.Crypto;

public class BasePacket {
	private static final int const1 = 17767; // 0x4567
	private static final int const2 = -30293; // 0x89ab
	
	private int opcode;
	private boolean shouldBuildHeader = false;

	private byte[] header;
	private byte[] data;
	
	// Encryption
	private boolean useDispatchKey;
	public boolean shouldEncrypt = true;
	
	public BasePacket(int opcode) {
		this.opcode = opcode;
	}
	
	public BasePacket(int opcode, int clientSequence) {
		this.opcode = opcode;
		this.buildHeader(clientSequence);
	}
	
	public BasePacket(int opcode, boolean buildHeader) {
		this.opcode = opcode;
		this.shouldBuildHeader = buildHeader;
	}

	public int getOpcode() {
		return opcode;
	}

	public void setOpcode(int opcode) {
		this.opcode = opcode;
	}

	public boolean useDispatchKey() {
		return useDispatchKey;
	}

	public void setUseDispatchKey(boolean useDispatchKey) {
		this.useDispatchKey = useDispatchKey;
	}

	public byte[] getHeader() {
		return header;
	}

	public void setHeader(byte[] header) {
		this.header = header;
	}

	public boolean shouldBuildHeader() {
		return shouldBuildHeader;
	}

	public byte[] getData() {
		return data;
	}

	public void setData(byte[] data) {
		this.data = data;
	}
	
	public void setData(GeneratedMessageV3 proto) {
		this.data = proto.toByteArray();
	}
	
	@SuppressWarnings("rawtypes")
	public void setData(GeneratedMessageV3.Builder proto) {
		this.data = proto.build().toByteArray();
	}
	
	public BasePacket buildHeader(int clientSequence) {
		if (this.getHeader() != null && clientSequence == 0) {
			return this;
		}
		setHeader(PacketHead.newBuilder().setClientSequenceId(clientSequence).setTimestamp(System.currentTimeMillis()).build().toByteArray());
		return this;
	}
	
	public byte[] build() {
		if (getHeader() == null) {
			this.header = new byte[0];
		}
		
		if (getData() == null) {
			this.data = new byte[0];
		}
		
		ByteArrayOutputStream baos = new ByteArrayOutputStream(2 + 2 + 2 + 4 + getHeader().length + getData().length + 2);
		
		this.writeUint16(baos, const1);
		this.writeUint16(baos, opcode);
		this.writeUint16(baos, header.length);
		this.writeUint32(baos, data.length);
		this.writeBytes(baos, header);
		this.writeBytes(baos, data);
		this.writeUint16(baos, const2);
		
		byte[] packet = baos.toByteArray();
		
		if (this.shouldEncrypt) {
			Crypto.xor(packet, this.useDispatchKey() ? Crypto.DISPATCH_KEY : Crypto.ENCRYPT_KEY);
		}

		return packet;
	}
	
	public void writeUint16(ByteArrayOutputStream baos, int i) {
		// Unsigned short
        baos.write((byte) ((i >>> 8) & 0xFF));
        baos.write((byte) (i & 0xFF));
    }
	
	public void writeUint32(ByteArrayOutputStream baos, int i) {
    	// Unsigned int (long)
        baos.write((byte) ((i >>> 24) & 0xFF));
        baos.write((byte) ((i >>> 16) & 0xFF));
        baos.write((byte) ((i >>> 8) & 0xFF));
        baos.write((byte) (i & 0xFF));
    }
	
	public void writeBytes(ByteArrayOutputStream baos, byte[] bytes) {
    	try {
			baos.write(bytes);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
    }
}