Add Send Operation

[sbernard31]

This aims to add support of Send Operation to Leshan.

See LWM2M specification for more details :

• core§6.4.6-Send-Operation
• transport§6.4.5-Infomation-Reporting-Interface

The API look like this :

Client Side:

// send data
SendResponse r = client.sendData (server,
                                  ContentFormat.SENML_JSON, 
                                  Arrays.asList("/3/0/1", "/3/0/2"),
                                  timeoutInMs);

Server Side:

// listen for new data
server.getSendService().addListener(new SendListener() {
  @Override
  public void dataReceived(Registration registration, Map<LwM2mPath, LwM2mNode> data, SendRequest request) {
      System.out.println(data);
  }
});

List of concerns or potential improvements :

• at client side, add more low level function allowing to send SendRequest directly.
• at server side, current Map<LwM2mPath, LwM2mNode> data is not so good. LwM2mPath is largely used internally but generally not so exposed. (we have same problem with WriteComposite)
• at server side, if an error occurred when handling SendRequest, this is not reported to application layer, it should maybe be reported in SendListener.
• at server side, in addition of listener maybe we should add a kind of DataCollector which could be able to report the data handling state. This could be useful to let device know when data was not collected/handled correctly.

[sbernard31]

I changed the Send API at server side like this :

// listen for new data
server.getSendService().addListener(new SendListener() {
  @Override
  public void dataReceived(Registration registration, Map<String, LwM2mNode> data, SendRequest request) {
      System.out.println(data);
  }
});

(data attribute changed from Map<LwM2mPath, LwM2mNode> to Map<String, LwM2mNode> data)

[sbernard31]

Still not entirely satisfied by the API an maybe we should go to something like #981.