Fix panic when assign to nil header and cookie when host is not found

[chojs23]

What?

When a request fails, the Response object is still returned but previously the Headers and Cookies maps were nil.

Why?

Trying to assign to a nil map causes a panic. Now these maps are always initialized, so users can safely modify them even for failed requests.

Checklist

• I have performed a self-review of my code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have added tests for my changes.
• I have run linter and tests locally (make check) and all pass.

Checklist: Documentation (only for k6 maintainers and if relevant)

Please do not merge this PR until the following items are filled out.

• I have added the correct milestone and labels to the PR.
• I have updated the release notes: link
• I have updated or added an issue to the k6-documentation: grafana/k6-docs#NUMBER if applicable
• I have updated or added an issue to the TypeScript definitions: grafana/k6-DefinitelyTyped#NUMBER if applicable

Related PR(s)/Issue(s)

Closes #5213

[inancgumus]

Hi @chojs23, thanks for the contribution!

Can you add a test to reproduce this issue to avoid future regressions?

When a request fails, the Response object is still returned but previously the Headers and Cookies maps were nil. Trying to assign to a nil map causes a panic. Now these maps are always initialized, so users can safely modify them even for failed requests.

[chojs23]

Hi @inancgumus, I added some tests.

[inancgumus]

Thanks for adding the tests. All LGTM but one thing.

[inancgumus]

Can you use the NewResponse function here? Other than that, your PR is LGTM.

[chojs23]

@inancgumus Thanks for review!

[AgnesToulet]

This is actually breaking a test because we expect the body to be null here: https://github.com/grafana/k6/blob/master/js/modules/k6/http/request_test.go#L2256 so I think this should be added in both places.

[inancgumus]

@chojs23, sure. Can you check @AgnesToulet's suggestion please?

[chojs23]

@inancgumus Creating Response with NewResponse function initialize body with empty array but this could break TestBinaryResponseWithStatus0 test as @AgnesToulet mentioned.

Hmm, Can we change the initial body null to empty array? I don't know the original code that creating Response with nil body was intended.

[AgnesToulet]

I'd prefer to keep the original behavior as users could rely on checking if the response body is null in some cases.

[inancgumus]

To keep the original behavior, can you revert the last commit? Thank you!

[chojs23]

Sure, I reverted it.