/**
	 * CoAP defines four types of messages:
	 * Confirmable, Non-confirmable, Acknowledgment, Reset.
	 */
	public enum Type {

		/** The Confirmable. */
		CON(0),

		/** The Non-confirmable. */
		NON(1),

		/** The Acknowledgment. */
		ACK(2),

		/** The Reject. */
		RST(3);

		/** The integer value of a message type. */
		public final int value;
	}

/**
	 * The enumeration of request codes: GET, POST, PUT and DELETE.
	 */
	public enum Code {

		/** The GET code. */
		GET(1),

		/** The POST code. */
		POST(2),

		/** The PUT code. */
		PUT(3),

		/** The DELETE code. */
		DELETE(4);

		/** The code value. */
		public final int value;
	}

/** The Constant NONE in case no MID has been set. */
	public static final int NONE = -1;
	/**
	 * The largest message ID allowed by CoAP.
	 * <p>
	 * The value of this constant is 2^16 - 1.
	 */
	public static final int MAX_MID = (1 << 16) - 1;

	/** The type. One of {CON, NON, ACK or RST}. */
	private CoAP.Type type;

	/** The 16-bit Message Identification. */
	private volatile int mid = NONE; // Message ID

	/**
	 * The token, a 0-8 byte array.
	 * <p>
	 * This field is initialized to {@code null} so that client code can
	 * determine whether the message already has a token assigned or not. An
	 * empty array would not work here because it is already a valid token
	 * according to the CoAP spec.
	 */
	private volatile Token token = null;

	/** The set of options of this message. */
	private OptionSet options;

	/** The payload of this message. */
	private byte[] payload;

	/**
	 * Destination endpoint context. Used for outgoing messages.
	 */
	private volatile EndpointContext destinationContext;

	/**
	 * Source endpoint context. Used for incoming messages.
	 */
	private volatile EndpointContext sourceContext;

	/** Indicates if the message has sent. */
	private volatile boolean sent;

	/** Indicates if the message has been acknowledged. */
	private volatile boolean acknowledged;

	/** Indicates if the message has been rejected. */
	private volatile boolean rejected;

	/** Indicates if the message has been canceled. */
	private volatile boolean canceled;

	/** Indicates if the message has timed out */
	private volatile boolean timedOut; // Important for CONs

	/** Indicates if the message is a duplicate. */
	private volatile boolean duplicate;

	/** Indicates if sending the message caused an error. */
	private volatile Throwable sendError;

	/** The serialized message as byte array. */
	private volatile byte[] bytes;

/**
	 * Convenience factory method to construct a POST request and equivalent to
	 * <code>new Request(Code.POST);</code>
	 * 
	 * @return a new POST request
	 */
	public static Request newPost() {
		return new Request(Code.POST);
	}

	/**
	 * Convenience factory method to construct a PUT request and equivalent to
	 * <code>new Request(Code.PUT);</code>
	 * 
	 * @return a new PUT request
	 */
	public static Request newPut() {
		return new Request(Code.PUT);
	}

	/**
	 * Convenience factory method to construct a DELETE request and equivalent
	 * to <code>new Request(Code.DELETE);</code>
	 * 
	 * @return a new DELETE request
	 */
	public static Request newDelete() {
		return new Request(Code.DELETE);
	}

/**
	 * Creates a response to the provided received request with the specified
	 * response code. The destination endpoint context of the response will be
	 * the source endpoint context of the request. Type and MID are usually set
	 * automatically by the {@link ReliabilityLayer}. The token is set
	 * automatically by the {@link Matcher}.
	 *
	 * @param receivedRequest the request
	 * @param code the code
	 * @return the response
	 * @throws IllegalArgumentException if request has no source endpoint
	 *             context.
	 */
	public static Response createResponse(Request receivedRequest, ResponseCode code) {
		if (receivedRequest.getSourceContext() == null) {
			throw new IllegalArgumentException("received request must contain a source context.");
		}
		Response response = new Response(code);
		response.setDestinationContext(receivedRequest.getSourceContext());
		return response;
	}

protected void work() throws IOException {
			datagram.setLength(size);
			socket.receive(datagram);
			LOGGER.debug("UDPConnector ({}) received {} bytes from {}:{}",
					new Object[]{socket.getLocalSocketAddress(), datagram.getLength(),
						datagram.getAddress(), datagram.getPort()});
			byte[] bytes = Arrays.copyOfRange(datagram.getData(), datagram.getOffset(), datagram.getLength());
			RawData msg = RawData.inbound(bytes, new AddressEndpointContext(datagram.getAddress(), datagram.getPort()), false);

			receiver.receiveData(msg);
		}

2.05
{"Content-Format":"text/plain"}
Hello CoAP!This is from Java coap server

Advanced

==[ CoAP Response ]============================================
MID    : 26037
Token  : [6243fee1521b9e40]
Type   : ACK
Status : 2.05
Options: {"Content-Format":"text/plain"}
RTT    : 43333 ms
Payload: 40 Bytes
---------------------------------------------------------------
Hello CoAP!This is from Java coap server
===============================================================