feat: add initial requestThingDescription implementation

[JKRhb]

This PR adds an initial implementation for the requestThingDescription method.

The implementation details probably still need some additional discussion – looking forward to your feedback here :) For now, I extended the ProtocolClient interface with a new requestThingDescription method that is expected to return a Content object that is deserialized and (supposed to be ) validated by the WoT implementation.

I think this latter part also touches #1055 – in my opinion, there should be some validation happening so that library users can be sure that they always receive a valid Thing Description. Maybe the algorithm(s) in the Scripting API would need to be adjusted then as well.

For now, I only implemented the protocol-specific requestThingDescription method for HTTP and CoAP, if the general design works for you more protocols could be added in follow-up PRs.

[codecov]

Codecov Report

Attention: 90 lines in your changes are missing coverage. Please review.

Comparison is base (a494687) 76.67% compared to head (5aeb45d) 76.33%.
Report is 3 commits behind head on master.

Files	Patch %	Lines
packages/binding-file/src/file-client.ts	18.60%	35 Missing ⚠️
packages/binding-coap/src/coap-client.ts	27.77%	13 Missing ⚠️
packages/core/src/wot-impl.ts	18.75%	13 Missing ⚠️
packages/binding-coap/src/coaps-client.ts	29.41%	12 Missing ⚠️
packages/binding-http/src/http-client-impl.ts	41.66%	7 Missing ⚠️
packages/binding-mbus/src/mbus-client.ts	71.42%	2 Missing ⚠️
packages/binding-modbus/src/modbus-client.ts	71.42%	2 Missing ⚠️
packages/binding-mqtt/src/mqtt-client.ts	71.42%	2 Missing ⚠️
packages/binding-netconf/src/netconf-client.ts	71.42%	2 Missing ⚠️
...ackages/binding-opcua/src/opcua-protocol-client.ts	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1166      +/-   ##
==========================================
- Coverage   76.67%   76.33%   -0.35%     
==========================================
  Files          80       80              
  Lines       16625    16827     +202     
  Branches     1603     1616      +13     
==========================================
+ Hits        12748    12845      +97     
- Misses       3847     3952     +105     
  Partials       30       30              

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[relu91]

I would fix Ege's point and I left a couple of comments below. Moreover, I wondering if we can somehow track the different TODOs comments before merging. Maybe when we reched two accepts we can create the issues and do a quick update of the comments with a link to the issues? Finally, maybe I missed why there is so much discrepancy between coaps and coap implementation?

[JKRhb]

Finally, maybe I missed why there is so much discrepancy between coaps and coap implementation?

That is actually because we are currently using two different libraries for CoAP (node-coap) and CoAPS (node-coap-client) since node-coap does not support DTLS :/ A mid-term goal for me personally is definitely to arrive at a unified implementation that covers not only CoAP and CoAPS but also CoAP over TCP/TLS and WebSockets. For the time being, though, I think we need to live with this doubled CoAP implementation.

[danielpeintner]

I think for an initial implementation it is fine as is.

I added some comments below

[danielpeintner]

LGTM

[relu91]

Good enough for now. Let's improve it with future iterations!