fix(HttpResponse): forward cookies only when response is used

[kettanaito]

Currently, we are forwarding the mocked response cookies onto document.cookie as a part of the HttpResponse constructor. That means that even constructing an HttpResponse instance will immediately forward its Set-Cookie onto document.cookie, even if that response never gets used (e.g. is conditional).

Changes

• HttpResponse no longer forwards its Set-Cookie onto document.cookie in the constructor.
• Response cookie forwarding is moved down to RequestHandler.run and applies only to the mocked response getting used.

[coderabbitai]

📝 Walkthrough

Walkthrough

Request handling now supports optional mocked responses and forwards raw Set-Cookie strings to the browser via a new exported forwardResponseCookies. The internal kSetCookie symbol was made private, with getRawSetCookie exposing stored raw cookie strings; cookie storage reads via that helper.

Changes

Cohort / File(s)	Summary
Request Handler src/core/handlers/RequestHandler.ts	Widened resolver result type to `Response
HTTP Response Decorators src/core/utils/HttpResponse/decorators.ts	Made kSetCookie symbol private; removed headers-polyfill import/usage here; store raw set-cookie string on responses via internal symbol and added exported `getRawSetCookie(response: Response): string
Request Cookie Storage src/core/utils/request/storeResponseCookies.ts	Replaced direct Reflect.get(..., kSetCookie) access with getRawSetCookie(response) call before passing value to cookieStore.setCookie.
Browser Test Mocks test/browser/rest-api/request/request-cookies.mocks.ts	Modified /set-cookies MSW mock to construct an additional HttpResponse whose Set-Cookie header is set to must-not=be-set before returning the original response that echoes the request body.

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant RequestHandler
    participant MockedResponse
    participant forwardResponseCookies
    participant Document

    Client->>RequestHandler: send request
    RequestHandler->>MockedResponse: invoke resolver -> Response | undefined
    alt mocked Response present
        RequestHandler->>forwardResponseCookies: forwardResponseCookies(response)
        forwardResponseCookies->>MockedResponse: read raw Set-Cookie(s)
        forwardResponseCookies->>Document: assign each to document.cookie
    end
    RequestHandler->>Client: return mocked or proxied response

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 I found cookies in a mocked reply,
Snuck them to document under moonlit sky,
Symbols hid the crumbs so neat,
getRawSetCookie whispers what to eat,
Forwarded treats make the browser sigh 🍪

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: moving cookie forwarding from HttpResponse construction to actual response usage.
Description check	✅ Passed	The description is directly related to the changeset, explaining the problem (cookies forwarded on construction) and the solution (move forwarding to RequestHandler.run).
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/response-cookies-on-exhaust

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[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/msw@2728

commit: 5afdabf

[coderabbitai]

🧹 Nitpick comments (1)

src/core/handlers/RequestHandler.ts (1)

340-340: Prefer explicit Response narrowing before cookie forwarding.

At Line 353, the truthy check works in practice, but instanceof Response makes the contract explicit and safer for untyped consumers.

Suggested tweak

-    if (mockedResponse) {
+    if (mockedResponse instanceof Response) {
       forwardResponseCookies(mockedResponse)
     }

Also applies to: 353-355

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@src/core/handlers/RequestHandler.ts` at line 340, Replace the loose truthy
check used before cookie forwarding with an explicit Response type guard: ensure
the value returned where the code currently narrows with a truthy check is first
checked with "instanceof Response" (or a dedicated isResponse helper) before you
call response.clone()/forwardCookies or access Response properties; update the
Promise<Response | undefined> handling in RequestHandler (the code that
currently treats the resolved value as truthy) to branch on instanceof Response
and only forward cookies in that branch, returning undefined or handling other
cases otherwise.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@src/core/handlers/RequestHandler.ts`:
- Line 340: Replace the loose truthy check used before cookie forwarding with an
explicit Response type guard: ensure the value returned where the code currently
narrows with a truthy check is first checked with "instanceof Response" (or a
dedicated isResponse helper) before you call response.clone()/forwardCookies or
access Response properties; update the Promise<Response | undefined> handling in
RequestHandler (the code that currently treats the resolved value as truthy) to
branch on instanceof Response and only forward cookies in that branch, returning
undefined or handling other cases otherwise.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 209eb580-c94a-4edc-89ad-7c7f48544994

📥 Commits

Reviewing files that changed from the base of the PR and between 686d87d and 5afdabf.

📒 Files selected for processing (4)

• src/core/handlers/RequestHandler.ts
• src/core/utils/HttpResponse/decorators.ts
• src/core/utils/request/storeResponseCookies.ts
• test/browser/rest-api/request/request-cookies.mocks.ts

🚧 Files skipped from review as they are similar to previous changes (3)

• test/browser/rest-api/request/request-cookies.mocks.ts
• src/core/utils/request/storeResponseCookies.ts
• src/core/utils/HttpResponse/decorators.ts

[kettanaito]

Released: v2.14.0 🎉

This has been released in v2.14.0.

• 📄 Release notes
• 📦 View on npm

Get these changes by running the following command:

npm i msw@latest

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