Add an EndpointProvider at Server side for CoAP based on java-coap(fork)

[sbernard31]

This aims to experiment transport abstraction layer implementing another endpoint provider at Server side for CoAP based on java-coap(fork).

See more details at #1373.

[szysas]

There is no restart after stop, need to create new instance to start again.
Out of curiosity, what's the use case for restart?

[sbernard31]

To be honest I'm not so sure if this is really needed, I know that we use it in some tests (especially at LWM2M client side to simulate that device is sleeping).

Californium has a start / stop / destroy mechanism where stop means that's you can restart unlike destroy.
Stop is kind of "pause".

As Leshan was strongly tied to californium, we follow this API.
Then when I did first transport abstraction layer, I keep it...
Always easier to add feature than remove it, but maybe better to just keep start() and destroy(). 🤔

[sbernard31]

@szysas thx a lot for reviewing this 😉

[sbernard31]

I finally succeed to pass all CoAP (only) integration tests with Californium used at LWM2M client side and java-coap at LWM2M server side.

(Probably not exhaustive) Missing feature :

• composite operation because Patch, IPatch and Fetch is not implemented in java-coap but should be available soon (318fe3d92dd61555ac260d8c86a4c03bdaf85960) and should not be so hard to implement.
• observe can not be shared / persisted : probably the biggest issue. Shared 'observe relation' store at CoAP client side. open-coap/java-coap#36
• we can not stop then restart a endpoint based on java-coap.

[sbernard31]

With java-coap v6.12.0, I was able to :

• Remove some workaround using new API : ae98e56
• Add support of Composite operation : b52be48

Thx @szysas 🙏

[sbernard31]

I rebased this in master (several conflict especially because of Identity Refactoring)

There is also some observe code available at java_coap_server_observe which depends on "not yet released version" of java-coap

[sbernard31]

✔️ Observe relation can now be shared / persisted, since we use java-coap v6.18.0.

All integration test are OK ✔️, there are still some TODO in the code but I think this is now in a testable state.
So, I plan to integrate in master soon and so it will be available in sandbox.

[sbernard31]

This is now integrated in master.

java-coap endpoint is available in leshan-server-demo, see Server tab:

The port and host can be configured with options:

-jh, --java-coap-host=<jlocalAddress>
                  Set the local CoAP address of endpoint based on
                    java-coap library.
                  Default: any local address.
-jp, --java-coap-port=<jlocalPort>
                  Set the local CoAP port of endpoint based on java-coap
                    library.
                  Default: 5685