feat(network-activity-plugin): Override and mock network responses

[IanLuan]

Override and mock network responses

This feature is inspired by Chrome DevTools overrides. It allows developers to edit the response and see how their app behaves, without changing the backend. Currently, it’s possible to override the response body and status.

With local overrides, you can unblock your workflow by prototyping and testing changes and fixes without waiting for the backend, third-parties, or APIs to support them.

Demo:

Override.network.compressed.mp4

How it works

The DevTools and the app both store the overrides. Every time a response is overridden, the DevTools send it to the app. The overrides list is persisted in the DevTools’ local storage, so it survives app reloads. On the DevTools side, it’s stored in Zustand store; in the app, it’s stored in a registry. If a request has an override, the response body and status are monkey-patched during XMLHttpRequest interception. On load, the DevTools send all overrides stored in local storage to the app, keeping the data in sync.

---

Note

Adds editable, persisted HTTP response overrides (status/body) in DevTools that sync to the app and are applied via XHR interception at runtime.

• Core/Protocol:
  • Add RequestOverride type and set-overrides event in shared/client.
• React Native (runtime):
  • New overrides-registry to store URL→override mappings.
  • Extend XHRInterceptor with setOverrideCallback and invoke before listeners.
  • network-inspector uses overrides to monkey‑patch XMLHttpRequest response/status and responseType based on Content-Type.
  • useNetworkActivityDevTools listens for set-overrides to update registry.
• DevTools (store + wiring):
  • Zustand store now persists overrides (Map) to localStorage and exposes addOverride/clearOverride actions; sends set-overrides to app.
  • InspectorView sends current overrides on setup and when overrides change.
• UI:
  • Add CodeEditor and OverrideResponse components for editing overrides.
  • ResponseTab integrates override workflow (edit/save/clear) and action slot via updated Section.
  • RequestList and SidePanel indicate when a request/response has an override.

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[vercel]

@IanLuan is attempting to deploy a commit to the Callstack Team on Vercel.

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[V3RON]

Let's split the implementation into two components:
a) one for showing up real responses
b) one for showing up overrides

When user clicks 'override', the second component will be shown.

[IanLuan]

Moved override logic into a new component – 79695a6 . Let me know if you think I should change anything.

[V3RON]

Let's add some sort of version control system, so if we change the state in the future, we will have the option to purge the local state and replace it with the new one. A simple STORE_VERSION constant and a __version property should be sufficient. If there is a mismatch, we should ignore the persisted state.

[IanLuan]

Added the STORE_VERSION constant and applied it to the version attribute of zustand persist - 438db9b.

[V3RON]

Isn't handleRequestOverride already called in readystatechange? Should we verify that readyState has a specific value?

[IanLuan]

You're right, I moved the overrideCallback invocation outside of event listener. It's on the same level as sendCallback (da64858)

[cursor]

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[cursor]

Bug: Inefficient Handling and Incorrect JSON Parsing

The handleRequestOverride function's readystatechange listener applies overrides on every state change, causing inefficient, repeated property assignments and potential timing issues. Additionally, when responseType is 'json', request.response is incorrectly assigned a string instead of a parsed JSON object, which violates the XMLHttpRequest specification.

 

[cursor]

Bug: Override Component Fails with Invalid Status Codes

The OverrideResponse component saves NaN as the override status if the status code input is empty or contains non-numeric characters. This occurs because parseInt returns NaN in these cases, which can lead to unexpected behavior when applying the network override.