[Californium/CoAP/LWM2M]: Reusing message send endpoint for server not possible?

Question

I am building a tool that can send CoAP messages to another peer (different implementation), but I am having difficulties. I am using the CoAP library called "Californium" and am developing the tool in java/eclipse. Here's the deal: I send a message over californium's "default endpoint", which allows the system to make up a source-port for the UDP "connection". I want to listen on this same source-port using californium's Server object, but I am getting the following error:

SEVERE: Could not start endpoint
java.net.BindException: Address already in use

So my question is: how do I first send a CoAP message and start listening for other CoAP messages on the same socket using Californium?

Below is the java code for the client. What it does is "register" using a certain protocol layered on top of CoAP. After registering I want it to re-use the UDP socket for listening for subsequent messages of the entity I registered with earlier.

NOTE: The server part of the client works when I explicitly tell it to listen to a certain port (e.g. 5683), leave out the register part and test it with the Firefox Addon "Copper" (i.e. Copper can get to the /1 /1/1 /1/1/0 resources).

package com.example.l2mwm.client;

import java.net.InetSocketAddress;

import ch.ethz.inf.vs.californium.coap.CoAP.Code;
import ch.ethz.inf.vs.californium.coap.CoAP.ResponseCode;
import ch.ethz.inf.vs.californium.coap.CoAP;
import ch.ethz.inf.vs.californium.coap.Request;
import ch.ethz.inf.vs.californium.coap.Response;
import ch.ethz.inf.vs.californium.network.Endpoint;
import ch.ethz.inf.vs.californium.network.EndpointManager;
import ch.ethz.inf.vs.californium.server.Server;
import ch.ethz.inf.vs.californium.server.resources.CoapExchange;
import ch.ethz.inf.vs.californium.server.resources.Resource;
import ch.ethz.inf.vs.californium.server.resources.ResourceBase;

public class Main {

    public static void main(String[] args) {
        Endpoint endpoint;
        if ((endpoint = register()) != null) {
            listen(endpoint);
        } else {
            System.out.println("Couldn't register!");
        }
    }

    private static void listen(Endpoint endpoint) {
        InetSocketAddress sockAddress = endpoint.getAddress();
        int port = sockAddress.getPort();
        Server server = new Server(port);
        Resource topResource = new ResourceBase("1") {
            @Override
            public void handleGET(CoapExchange exchange) {
                exchange.respond(ResponseCode.CONTENT, "this is /1's value!");
            }

            @Override
            public String getPath() {
                return "/";
            }
        };

        Resource instanceResource = new ResourceBase("1") {
            @Override
            public void handleGET(CoapExchange exchange) {
                exchange.respond(ResponseCode.CONTENT, "this is /1/1's value!");
            }

            @Override
            public String getPath() {
                return "/1/";
            }
        };

        topResource.add(instanceResource);

        instanceResource.add(new ResourceBase("0") {
            @Override
            public void handleGET(CoapExchange exchange) {
                exchange.respond(ResponseCode.CONTENT, "this is /1/1/0's value!");
            }

            @Override
            public String getPath() {
                return "/1/1/";
            }
        });

        server.add(topResource);

        server.start();
    }

    private static Endpoint register() {
        Request request = new Request(Code.POST);
        request.setURI("localhost:5684/rd?ep=coapclient&lt=86400&b=U");
        request.setPayload("</1/1/0>");
        Endpoint endpoint = EndpointManager.getEndpointManager().getDefaultEndpoint();
        request.send(endpoint);

        Response response;
        ResponseCode responseCode = null;

        try {
            response = request.waitForResponse();
        } catch (InterruptedException e) {
            System.out.println(e.getMessage());
            return null;
        }

        responseCode = response.getCode();
        if (responseCode != CoAP.ResponseCode.CREATED) {
            return null;
        }

        return endpoint;
    }

}

Answer 1

You need to first bind your UDP socket and then start your LWM2M register.

Because what you do: create CoAP Endpoint (bind a udp server) and than you bind again in your listen method.

  // list to the UDP post 5555
  coapServer = new Server();
  Endpoint endpoint = new CoAPEndpoint(new InetSocketAddress("localhost",5555);
  coapServer.addEndpoint(endpoint);

  // send a message to a LWM2M server:
  request request = new Request(Code.POST);
  request.setURI("iot.eclipse.org:5683/rd?ep=coapclient&lt=86400&b=U");
  request.setPayload("</1/1/0>");
  Endpoint endpoint = EndpointManager.getEndpointManager().getDefaultEndpoint();
  request.send(endpoint);

You can still access to your client using copper on coap://localhost:5555