feat(event-handler): add streaming functionality

[svozza]

Summary

This PR adds the logic for returning streaming HTTP responses as currently supported by Lambda Function URLs. As event-handler does not currently support Function URLs, we are not exposing the final streamify function that users will use to enable streaming:

import {Router, streamify} from '@aws-lambda-powertools/event-handler/experimental-rest';

const app = new Router(); 

// ...

app.get('/test', ({event}) => {
  return {
    headers: {
      'content-type': 'application/json'
    },
    statusCode: 200,
    body: Readable.from(Buffer.from(JSON.stringify(event)))
  }
});

// ...

export handler = streamify(app);

This means that we will not have to have a long lived branch with the logic for this feature while we wait on Function URL support.

Changes

• Add new resolveStream method that takes a Lambda ResponseStream as one of its arguments
• Adds support for returning both Nodejs and web streams from middleware and route handlers but only when returned as a valid APIGatewayProxyResult type.
• Unit tests for resolveStream method and assoicated helper functions.

Issue number: closes #4476

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Disclaimer: We value your time and bandwidth. As such, any pull requests created on non-triaged issues might not be successful.

[dreamorosi]

Thank you for the PR - I'll need a day or two to review and test it.

Looking forward to streaming!

[sdangol]

added a few minor comments and questions

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
3.9% Duplication on New Code

See analysis details on SonarQube Cloud

[dreamorosi]

Amazing work, this is really nice.

We should write a small short blog post on Builder Hub about this.