fix(microservices): grpc client closing

[yurks]

PR Checklist

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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?

Currently, using GRPC client created through ClientProxyFactory, it's not possible to close once initiated connection.

const client = ClientProxyFactory.create({
      transport: Transport.GRPC
    });

const service = client.getService('ServiceName')

await firstValueFrom(service.callSomething())

// do nothing with connection
client.close()

// workaround to close connection properly
client.getClientByServiceName<Client>('ServiceName').close();

That looks like a bug, as close() method of ClientGrpcProxy class trying to call corresponding method not from Client instance, created by @grpc/grpc-js, but from parsed proto package definition, loaded by @grpc/proto-loader:

  // ! there is packages definitions inside this.grpcClients, not a clients
  public close() {
    this.grpcClients
      .filter(client => client && isFunction(client.close))
      .forEach(client => client.close());
    this.grpcClients = [];
  }

As a result, network connection to GRPC server never ends, once initiated.

Additionally, connections are not gratefully closing on app termination, using GRPC client via ClientsModule, as above described method set for client.onApplicationShutdown hook:

    static assignOnAppShutdownHook(client) {
        client.onApplicationShutdown =
            client.close;
        return client;

Issue Number: N/A

What is the new behavior?

public close() method has been rewritten to properly close the network connection.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[coveralls]

Pull Request Test Coverage Report for Build c3aa89dd-6768-4bd8-bcb3-9213772bcb6e

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.001%) to 92.101%

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Totals
Change from base Build 7ac098a9-c60b-4faa-9612-e3dbed2e2eb6:	0.001%
Covered Lines:	6716
Relevant Lines:	7292

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💛 - Coveralls

[kamilmysliwiec]

any chance we could keep using filter & forEach combination instead of an inline && condition?

[yurks]

this.clients is a map, and there is no .filter
Sure, we can convert map to array here, then filter, then foreach over it, but I found this approach too complicated for this functionality

[kamilmysliwiec]

so instead of using an inline condition could we just use a regular if statement here? (for better readability)

[yurks]

changed