Mastering Static Files: Middleware and 100% Test Coverage

Serving static assets efficiently is a cornerstone of web development. Today, we're introducing the staticFiles middleware for Fastro—a robust solution designed for performance and reliability.

Key Features

The new static middleware isn't just a simple file server. It's built with modern production requirements in mind:

• Intelligent LRU Caching: In production mode (ENV=production), Fastro caches files in memory using a Least Recently Used (LRU) eviction strategy. This drastically reduces disk I/O for frequently accessed assets.
• SPA Fallback: A critical feature for modern Single Page Applications (React, Vue, Svelte, etc.).
  • The Problem: In SPAs, routing is handled on the client side. If a user refreshes the page at /dashboard, the server looks for a physical file named dashboard which doesn't exist, resulting in a 404 error.
  • The Solution: With spaFallback: true, the server automatically serves index.html when a requested file is missing. This allows the client-side router (e.g., React Router) to take over and render the correct component based on the URL.
• Auto MIME Mapping: Support for a wide range of extensions out of the box, from standard .html and .js to modern web fonts (.woff2, .ttf).
• Cache Control: Intelligent headers based on the environment, ensuring browsers cache assets effectively in production while allowing developers to see changes instantly in development.

Engineering Excellence: 100% Coverage

Software reliability is non-negotiable at Fastro. To ensure the staticFiles middleware works flawlessly under all conditions, we've implemented a comprehensive test suite.

Using the Deno.test runner and @std/testing/time's FakeTime, we've achieved 100% test coverage for both lines and branches.

What we tested:

• Root & Subdirectory Serving: Ensuring files are found regardless of path depth.
• Cache Expiry Logic: Using virtual time to verify that cached items are correctly invalidated after 1 hour.
• LRU Eviction: Simulating heavy load to confirm that the cache respects its 100-file limit.
• Security & Method Handling: Verifying that only GET requests are served and prefixes are strictly enforced.

How to Use

Adding static file support to your Fastro app is now easier than ever:

import { Fastro } from "https://deno.land/x/fastro/mod.ts";
import { staticFiles } from "https://deno.land/x/fastro/middlewares/static/static.ts";

const app = new Fastro();

// Serve files from the 'public' folder at the '/static' URL prefix
app.use(staticFiles("/static", "./public", { spaFallback: true }));

await app.serve();

Conclusion

With the addition of the static middleware and our commitment to 100% test coverage, Fastro continues to provide a solid foundation for building high-performance web applications.

Stay tuned for more updates as we continue to refine the framework!