Add Write Composite Operation

[sbernard31]

This aims to add Write Composite support.

Atomicity at client side is not supported.

API at server side looks like :

Map<String, LwM2mNode> nodes = new HashMap<>();
nodes.put("/3/0/14", LwM2mSingleResource.newStringResource(14, "+02"));
nodes.put("/1/0/2", LwM2mSingleResource.newIntegerResource(2, 100));

WriteCompositeResponse response = server.send(helper.getCurrentRegistration(),
        new WriteCompositeRequest(ContentFormat.SENML_COBOR, nodes));

This is not so good because resource Id is duplicate but for now I didn't find a better idea.

(This is a work in progress)

[sbernard31]

This is probably not perfect but I think it's now in reviewable/testable state.

The WriteCompositeRequest API at server side is still not so good. Ideas are welcomed.

At client side :

• There isn't real transaction support for atomicity. Maybe we need a kind of rollback/commit support ? Transactional API at client side #968
• We probably also need a new kind of synchronization, locking/synchronized at Object level could be not enough. Enhance LWM2M tree synchronizaton mechanism at client side #967

[sbernard31]

I changed the WriteCompositeRequest API to avoid this double Id issue, this looks like :

Map<String, Object> nodes = new HashMap<>();
nodes.put("/3/0/14", "+02");
nodes.put("/1/0/2", 100);

WriteCompositeResponse response = server.send(helper.getCurrentRegistration(),
        new WriteCompositeRequest(ContentFormat.SENML_COBOR, nodes));

[sbernard31]

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