feat(microservices): Add grpc metadata to server responce

[AlexDaSoul]

#5098 PR Checklist
Please check if your PR fulfills the following requirements:

• 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
[x] 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?

Cannot send metadata from @GrpcMethod

Issue Number: #1897

What is the new behavior?

import { Metadata } from 'grpc';

@GrpcMethod('Service', 'Method')
public method(request: any, metadata: Metadata, sendMetadata: Function): any {
   // 1. nothing to do with request that is empty in this case
   // 2. may something with metadata from client if needed
   // 3. send metadata with responce........
   const srvMetadata = new Metadata();

   srvMetadata.add('Set-Cookie', 'yummy_cookie=choco');

   sendMetadata(srvMetadata);

   return 'Hello World!!!';
}

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[coveralls]

Pull Request Test Coverage Report for Build d8106f42-dec7-49a5-bd41-01fe82ee1392

• 4 of 5 (80.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.02%) to 94.8%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/microservices/factories/rpc-params-factory.ts	0	1	0.0%

Totals
Change from base Build df8fd14f-cb6a-4c1f-a4b6-051ea09e4baa:	-0.02%
Covered Lines:	4922
Relevant Lines:	5192

---

💛 - Coveralls

[kamilmysliwiec]

Would you like to create a PR to the docs with this feature?

[AlexDaSoul]

Would you like to create a PR to the docs with this feature?

Sure, I will do it

[AlexDaSoul]

Would you like to create a PR to the docs with this feature?

@kamilmysliwiec done nestjs/docs.nestjs.com#1386

[tchambard]

@AlexDaSoul Is there a way to get these metadata from the response on the client side when using nestjs grpc client ? When I look into the code, it seems not, but maybe I'm missing something ?

[AlexDaSoul]

@AlexDaSoul Is there a way to get these metadata from the response on the client side when using nestjs grpc client ? When I look into the code, it seems not, but maybe I'm missing something ?

There is no direct option, but we can get metadata using the event 'metadata' of client

const client = new proto.MyService(host, creds);

call = client.GrpcMethod({ //... });
call.on('metadata', (metadata) => console.log(metadata));
call.on('data', fillSnapshot);
call.on('end', () => console.log('end'));
call.on('cancelled', () => console.log('cancelled'));
call.on('error', (err) => console.log(err));

[tchambard]

Ok. Thanks