feat(sse): Implement Server-Sent Events

[soyuka]

PR Checklist

• 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

[x] Feature see #4826

See discussion in #4826. You can test this using the new sample 28.

Usage:

@Controller()
export class AppController {
  @Get()
  getHello(): string {
    return `
    <script type="text/javascript">
      const ee = new EventSource('/sse')
      ee.onmessage = ({data}) => {
        console.log('New message', JSON.parse(data))
      }
    </script>
    `;
  }

  @Sse('/sse')
  sse(): Observable<MessageEvent> {
    return interval(1000).pipe(map((_) => ({ data: { hello: 'world' } })));
  }
}

[kamilmysliwiec]

Can we remove the 28-sse? I don't think it makes sense to create a separate sample for this (likewise, we don't have dedicated samples for @Redirect() or any similar decorators)

[soyuka]

I see this @sse directive as we could see the Websocket one. I think that this may serve as a functional test or a test application to understand how it works and to understand that it can be used for real-time updates.

[coveralls]

Pull Request Test Coverage Report for Build 1eed7a91-71e0-4b54-963b-382fb2a112fe

• 62 of 63 (98.41%) changed or added relevant lines in 7 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 94.859%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/core/services/sse-stream.service.ts	28	29	96.55%

Totals
Change from base Build e71e44e4-8e59-4613-8899-b4e4a3d5c916:	0.04%
Covered Lines:	4982
Relevant Lines:	5252

---

💛 - Coveralls

[kamilmysliwiec]

The overall API looks good! Would you like to create a PR to the docs? We can add it under the "Techniques" category (as a new, dedicated page) or just add a new section in the "Controllers" chapter

[soyuka]

see nestjs/docs.nestjs.com#1387 lmk if I should rebase

[soyuka]

rebased and added docs

[jdgriffith]

Any chance this will land soon? Our team could use this feature :)

[soyuka]

Any chance this will land soon? Our team could use this feature :)

Would you be able to test my branch and make some feedbacks?

[mfcodeworks]

Any chance for this being merged soon? Would love to provide SSE updates to clients

[lukeheath]

Same here! This will be a great feature add for the framework.

[soyuka]

Any chance for this being merged soon? Would love to provide SSE updates to clients
Same here! This will be a great feature add for the framework.

Same comment as above: Would you be able to test my branch and make some feedbacks?

[soyuka]

I have benchmarks where this hits 80k req/s pushed on a single node. I'd love to know what maintainers think of this work!

[kamilmysliwiec]

Thank you for this amazing contribution! This feature will be available in 7.5.0

[ruslanguns]

Nice feature! Thank you !

[ningacoding]

Hello, how do you send data from a service? to an already subscribed client.

i tried but observables only works in the method scope and when trying to emit data from another endpoint (for example, when another user/client is updating data) the observable just do not emit to the other client to receive the update.

[kamilmysliwiec]

Please, use our Discord channel (support) for such questions. We are using GitHub to track bugs, feature requests, and potential improvements.