Request Context Store (request-context.js)

💡 Overview

Unlike Client Components (which query the active tab url or browser storage), Server Components compile on-demand for incoming requests. A component deep inside the React tree might need to query cookie tokens or headers without passing parameters through props from top-level layouts.

The request-context.js file provides this functionality. It leverages Node's AsyncLocalStorage to store request-scoped data (like headers, search params, and cookies), exposing a clean getContext() accessor.

📊 Context Scope Flow

The flowchart below shows how request contexts are isolated and retrieved:

⚡ AsyncLocalStorage & Isolation

In standard Node.js scripts, global variables are shared across all requests. Under high traffic, storing request data in globals would cause **cross-talk bugs** (e.g. User A receives User B's private account data).

Dinou prevents this via AsyncLocalStorage:

• Thread Isolation: Associates request state maps ({ req, res }) with asynchronous execution chains. When a Server Component executes an async operation, Node carries the context along automatically.
• Global Persistency: Binds storage instances using Symbol.for() on the global scope. This preserves request contexts during Hot Module Replacement (HMR) reloads.
• Safe Client Bypasses: Mocks execution APIs in browser threads, rendering warnings to developers if getContext() is called in Client Components.

⚙️ Complete Code Walkthrough

Below is the full, complete code of request-context.js:

// dinou/core/request-context.js

const DINOU_CONTEXT_KEY = Symbol.for("dinou.request.context.storage");
let requestStorage;

// 1. Initialize AsyncLocalStorage only on Server side
if (typeof window === "undefined") {
  const nodeRequire =
    typeof module !== "undefined" && typeof module.require === "function"
      ? module.require.bind(module)
      : null;

  if (nodeRequire) {
    const { AsyncLocalStorage } = nodeRequire("node:async_hooks");

    // Persist storage globally to prevent hot-reload wipes
    if (!global[DINOU_CONTEXT_KEY]) {
      global[DINOU_CONTEXT_KEY] = new AsyncLocalStorage();
    }

    requestStorage = global[DINOU_CONTEXT_KEY];
  }
} else {
  // 2. Client Side Fallback Mock: prevents errors during build/hydration passes
  requestStorage = {
    run: (store, callback) => callback(),
    getStore: () => undefined,
  };
}

function getContext() {
  if (typeof window !== "undefined") {
    console.error(
      "[Dinou] ❌ You are calling getContext() inside a Client Component running in the browser. " +
      "This function is Server-Only. Pass the data as props from a Server Component instead."
    );
    return {};
  }
  if (!requestStorage) return undefined;
  
  // 3. Retrieve the context map associated with the active execution thread
  const store = requestStorage.getStore();
  return store;
}

module.exports = {
  requestStorage,
  getContext,
};