Use isObervable from rxjs instead of our own implementation. Drop few deprecated APIs from 3rd-party libs. And other minor refactorings

[micalevisk]

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Issue Number: closes #8595

As you can see here: https://cs.github.com/nestjs/nest?&q=isObservable there are few versions of isObservable on this codebase. Which are implemented as follow:

function isObservable(input): input is Observable<any> {
  return input && isFunction(input.subscribe)
}

I'm under assumption that all of them are supposed to return true when the input is an Observable object created by rxjs lib.

What is the new behavior?

Using isObservable type guard from rxjs instead (introduced in rxjs@6)

which is implemented as follows here:

function isObservable<T>(obj: any): obj is Observable<T> {
  return !!obj && (obj instanceof Observable || (isFunction(obj.lift) && isFunction(obj.subscribe)))
}

thus, I believe this should fix the linked Issue.

I've fixed the return type of Server#transformToObservable as well:

before

now

---

Also, I've used eslint-plugin-deprecation to detected and remove deprecated APIs of rxjs and body-parser and ones related with Buffer (nodejs). The latter only touches .spec.ts files.

Does this PR introduce a breaking change?

• Yes
• No

Do notice that, basically:

• before: obj is observable when isFunction(obj.subscribe)
• now: obj is observable when isFunction(obj.subscribe) && isFunction(obj.lift)

I'm pretty sure this means that there are no breaking changes due to how isObservable is being used in this codebase but I could be wrong.

[coveralls]

Pull Request Test Coverage Report for Build d4447bdf-1f5d-4944-ba9e-8984ae03e7c3

• 26 of 27 (96.3%) changed or added relevant lines in 9 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.003%) to 94.126%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/microservices/server/server-grpc.ts	2	3	66.67%

Totals
Change from base Build f821b4c8-5d49-4afa-9ee8-5265f6c6b09b:	-0.003%
Covered Lines:	5689
Relevant Lines:	6044

---

💛 - Coveralls

[micalevisk]

I didn't wrote missing tests for server-grpc.ts because I'm not familiar with gRPC.

Also, I didn't really understand the following

nest/packages/microservices/server/server-grpc.ts

Lines 257 to 267 in 7825c02

	call.on('error', (e: any) => {
	// Check if error means that stream ended on other end
	const isCancelledError = String(e).toLowerCase().indexOf('cancelled');
	if (isCancelledError) {
	call.end();
	return;
	}
	// If another error then just pass it along
	req.error(e);
	});

because if (isCancelledError) will be evaluate to true when e !== 'canceled', which doesn't make sense to me.

[jmcdo29]

Looks good to me

[kamilmysliwiec]

LGTM