Packets4J

A lightweight abstract TCP/IP socket & packet library.

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Content

• Content

• Dependencies

• Packets

  • Data Blocks
  • Packet Build Order

• CodecManager

• EncryptionManager

  • Encryption
  • Decryption

• CompressionManager

  • Compression
  • Decompression

• Events

• Examples

• Compiling

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Dependencies

This project uses the following dependencies:

• JBCodec: Java Byte Codec >= v1.0

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Packets

A Packet<T> is an interface that represents a packet containing data of type T. The generic parameter T specifies the type of values that the packet encode and decode.
When working with packets, the T parameter allows you to define the specific type of data that the packet encapsulates. It provides a way to make the packet interface more flexible and reusable, as you can use different types for different packets.
The packet construction pattern consists of several elements that are used to construct a packet:

TYPE	LENGTH	NAME	DESCRIPTION
int	4B	LENGTH	The total Packet length, excluding the 4 bytes used to store the length itself.
int	4B	ID	The id of the Packet.
x	Variable	DATA	The data block(s) included in the packet.

The interface Packet implements 2 subinterfaces: S2CPacket<T> and C2SPacket<T>, to separate Server→Client and Client→Server communication.
The S2CPacket and C2SPacket could be registered with the same id as long as there is an outgoing (serverside) and an ingoing (clientside) Packet that take the same type of Object as input.
The server cannot send a S2CPacket<Object[]> with id 0, when the clients awaits a S2CPacket<String> as id 0. However, C2SPacket<String> (serverside) with id 0 would be a valid as long as the C2SPacket (clientside) also awaits a <String> with id 0.

This table represents a valid packet configuration:
(S/C : Server/Client where the packet was registered)

S/C	ID	TYPE	OBJECT
S	0	S2C	send T1
C	0	S2C	read T1
C	0	C2S	send T2
S	0	C2S	read T2

This table represents a wrong packet configuration:

S/C	ID	TYPE	OBJECT
S	0	S2C	send T2
C	0	S2C	read T1
C	0	C2S	send T2
S	0	C2S	read T3

Implementing S2CPacket and C2SPacket in the same subclass for the client and the server ensures that the awaited Object is the same for the two.

Data Blocks

The construction of a data block varies depending of the generic argument passed T, basic data blocks are defined as follows:

TYPE	LENGTH	NAME	DESCRIPTION
short	2B	HEADER	The header used to decode the following data, see CodecManager.
x	variable	DATA	The data of the block.

This definition is valable for generic types such as: Byte, Short, Integer, Double, Float, Long and Character, because their size is known. The header can be omitted in some cases, such as in arrays or maps where multiple following elements use the same header which is specified in the parent data block

Data blocks for types with variable size such as String, Arrays, Lists and Maps have a different construction:

TYPE	LENGTH	NAME	DESCRIPTION
short	2B	HEADER	The header used to decode the following data, see CodecManager.
int	4B	LENGTH	The length of the following data, see CodecManager.
x	variable	DATA	The data of the block.

Data blocks can be concatonated inside each other, for example a String[] (String array) is described this way:

TYPE	LENGTH	NAME	DESCRIPTION
short	2B	HEADER	The Array header.
int	4B	LENGTH	The count of elements contained int the array.
short	2B	HEADER	The String header.
x	variable	DATA	The data of the block.

This specific data is constructed this way:

TYPE	LENGTH	NAME	DESCRIPTION
int	4B	LENGTH	The length of the following String.
x	LENGTH	DATA	The bytes of the String.

Note that the Header is dropped because it is specified after the Array's length; the same decoder is used for all of the elements contained in the array.

Packet Build Order

Data Blocks generated by the CodecManager, are handed to the EncryptionManager and the CompressionManager.
These operations follow a specific order for writing the packet:

NAME	RETURNS	DESCRIPTION
new Packet<T>()	Packet	New packet instance created.
Packet#xWrite(x)	Object	The write method of the packet is called.
CodecManager#encode(Object)	ByteBuffer	The packet's content gets encoded by the corresponding Encoder<T>.
EncryptionManager#encoder(ByteBuffer)	ByteBuffer	The ByteBuffer gets encrypted using the registered Encryptor.
CompressionManager#compress(ByteBuffer)	ByteBuffer	The ByteBuffer gets compressed using the registered Compressor.
ADD LENGTH, ID	ByteBuffer	The length of the packet and it's ID is added.
write(ByteBuffer)	boolean	Writes the ByteBuffer to the OutputStream. Returns true if succeeded.

To read an incoming packet, the same operations are done in reverse.
Data Blocks are handed to the CompressionManager and the EncryptionManager:

NAME	RETURNS	DESCRIPTION
read(ByteBuffer (4))	int	Reads the input for 4 bytes. This represents the LENGTH of the following packet.
read(ByteBuffer (LENGTH))	int	Reads the input for LENGTH bytes.
PARSE ID	ByteBuffer	The 4 first bytes of the data represent the ID of the packet.
CompressionManager#decompress(ByteBuffer)	ByteBuffer	The ByteBuffer gets decompressed using the registered Decompressor.
EncryptionManager#decrypt(ByteBuffer)	ByteBuffer	The ByteBuffer gets decrypted using the registered Decryptor.
CodecManager#decode(Packet)	ByteBuffer	The packet's content gets decoded by the corresponding Decoder<T>.
PacketManager#packetInstance(ID)	Packet	New packet instance is created using it's id.
Packet#xRead(x, obj)	void	The packet is read by the receiver.

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CodecManager

See JBCodec's CodecManager.

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EncryptionManager

The EncryptionManager class is responsible for managing the encryption and decryption of the input and output ByteBuffers.

1. Encryptor getEncryptor(), Decryptor getDecryptor(): Getters for Encryptor/Decryptor.
2. void setEncryptor(Encryptor e), void setDecryptor(Decryptor d): Setters for Encryptor/Decryptor.
3. static EncryptionManager raw(): This static factory method creates and initializes a EncryptionManager instance with RawDecryptor and RawEncryptor, this does not encrypt.
4. static EncryptionManager aes(byte[] key): This static factory method creates and initializes a EncryptionManager instance using the AES symmetric key algorithm.

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CompressionManager

The CompressionManager class is responsible for managing the compressing and decompressing the input and output ByteBuffers.

1. Compressor getCompressor(), Decompressor getDecompressor(): Getters for Compressor/Decompressor.
2. void setCompressor(Compressor e), void setDecompressor(Decompressor d): Setters for Compressor/Decompressor.
3. static CompressionManager raw(): This static factory method creates and initializes a CompressionManager instance with RawCompressor and RawDecompressor, this does not compresses.

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Events

There are 2 default EventManagers:

• AsyncEventManager handles events asyncronously, in a separate thread pool.
• EventManager handles events syncronously, default EventManager.

Changing the default EventManager:
The default is SyncEventManager
P4JServer.setEventManager(<consumer>)
P4JCient.setEventManager(<consumer>)

Adding an EventListener:
P4JServer.getEventManager().register(<listener>)
P4JClient.getEventManager().register(<listener>)

EventListener usage:

• The @ListenerPriority (optional) annotation is used to change the listener's priority (higher = executed earlier, default is 0)
• The @EventHandler annotation is used to mark methods to handle the event specified by the first parameter. Example:

@ListenerPriority(priority = 10)
public class MyEventListener implements EventListener {
	@EventHandler
	public void onClientConnect(ClientConnectedEvent event) {
		// do something
	}
	// the name doesn't matter
	@EventHandler
	public void kjwdsfkjhsf(P4JEvent event) {
		// do something
	}
}

There are multiple events (implementing P4JEvent):

• ClientConnectedEvent(P4JClientInstance, P4JServerInstance): When a client connects to a server.
  Server side: ServerClient -> P4JServer
  Client side: P4JClient -> ClientServer
• S2CReadPacketEvent(P4JInstance, Packet, Class<Packet>, int, Throwable, boolean): When a client reads an incoming packet from the server.
• S2CWritePacketEvent(P4JClientInstance, Packet, Class<Packet>, int, Throwable, boolean): When a server writes an outgoing packet to the client.
• C2SReadPacketEvent(P4JClientInstance, Packet, Class<Packet>, int, Throwable, boolean): When a server reads an incoming packet from the client.
• C2SWritePacketEvent(P4JClientInstance, Packet, Class<Packet>, int, Throwable, boolean): When a client writes an outgoing packet to the server.
• ClosedSocketEvent(ClosedChannelException, P4JClientInstance): When a client connection gets closed.

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Examples

See Cat Dog Question Example

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Compiling

To compile use maven, implemented options are: test, package, install & defaults