feat(coap-server): add initial meta operation support

[JKRhb]

Based on the refactoring made in #1084, this PR adds initial support for meta operations, namely the reading of multiple or all properties, to the CoAP server. This corresponds with issue #1014 – as only one kind of meta operation is supported yet, I think the issue can be kept open for now.

I haven't figured out the correct way to implement writing multiple properties yet, which is why I left it out of this PR for now. However, a method skeleton already exists (at the moment, it simply returns an error response with code 5.01 (Not Implemented)) which can be expanded in a follow-up PR.

As this PR depends on #1084, I will rebase once that PR has been merged to make reviewing a bit easier. Until then, I will keep this PR in draft status.

[codecov]

Codecov Report

Patch coverage: 93.07% and project coverage change: +0.22% 🎉

Comparison is base (227be53) 75.31% compared to head (641cae5) 75.53%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1086      +/-   ##
==========================================
+ Coverage   75.31%   75.53%   +0.22%     
==========================================
  Files          80       80              
  Lines       16060    16172     +112     
  Branches     1503     1519      +16     
==========================================
+ Hits        12096    12216     +120     
+ Misses       3925     3917       -8     
  Partials       39       39              

Files Changed	Coverage Δ
packages/binding-coap/src/coap-server.ts	81.19% <93.07%> (+2.82%)	⬆️

... and 2 files with indirect coverage changes

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[egekorkan]

I haven't figured out the correct way to implement writing multiple properties yet, which is why I left it out of this PR for now.

You are not alone at this so it can definitely be postponed: w3c/wot-thing-description#848 . However, wouldn't it be better to never generate a TD with it?

[JKRhb]

However, wouldn't it be better to never generate a TD with it?

Good point, I removed it for now alongside the handleWriteMultipleProperties method in order to not confuse people. However, note that in the HTTP server, the write meta operations are actually added to the op array despite having no corresponding handler method defined:

node-wot/packages/binding-http/src/http-server.ts

Lines 346 to 366 in 227be53

	if (anyProperties) {
	const href = base + "/" + this.PROPERTY_DIR;
	const form = new TD.Form(href, type);
	if (allReadOnly && !allWriteOnly) {
	form.op = ["readallproperties", "readmultipleproperties"];
	} else if (allWriteOnly && !allReadOnly) {
	form.op = ["writeallproperties", "writemultipleproperties"];
	} else {
	form.op = [
	"readallproperties",
	"readmultipleproperties",
	"writeallproperties",
	"writemultipleproperties",
	];
	}
	if (!thing.forms) {
	thing.forms = [];
	}
	thing.forms.push(form);
	this.addUrlRewriteEndpoints(form, thing.forms);
	}

[relu91]

Just a small comment below. Test coverage could be also improved but we can do it in a future PR.

[relu91]

Actually, the spec is not clear about this semantic. One could still understand that the readallproperties operation just works on the set of readable properties of the thing. I guess for the time being is alright to leave as it is, but still other bindings implementations might act differently.