Express + Routing-Controllers on Firebase Functions

Overview

A lightweight, flexible approach to building a serverless API with Firebase Functions, leveraging the routing-controllers library in conjunction with Express.js. Unlike the heavier NestJS framework, which also builds upon routing-controllers and typedi, this setup opts for simplicity and flexibility, making it easier to understand and customize for your specific needs.

Why routing-controllers?

• Simplicity and Flexibility: Offers a straightforward way to define routes and middleware, making it easier to work with and adapt than more complex frameworks like NestJS.
• Compatibility: Seamlessly integrates with any Express application, allowing for the use of existing Express middleware and patterns.
• Dependency Injection: Utilizes typedi for dependency injection, simplifying the management of service instances and their dependencies.
• Reduced Overhead: Avoids the extra complexity and overhead introduced by frameworks like NestJS, focusing instead on the core functionalities needed for routing and control.

Project Structure

• Middleware: Custom middleware, such as LoggingMiddleware for logging requests and CustomErrorHandler for handling errors, can be globally applied before controller actions.
• Controllers: Business logic is encapsulated within controllers, e.g., ThingController, keeping the code organized and maintainable.
• Decorators: Utilizes decorators for routing, middleware, and dependency injection, making the code cleaner and more expressive.

Features

• Express Setup: Basic Express server setup with JSON body parsing and a simple root route.
• Global Middleware: Demonstrates how to use global middleware for logging and custom error handling.
• Dependency Injection: Shows how to integrate typedi for dependency injection in controllers and services.
• Custom Decorators: Implements custom decorators for authorization and current user context, showcasing the extensibility of routing-controllers.

Getting Started

1. Install Dependencies: Run npm install to install the required packages, including express, reflect-metadata, routing-controllers, and typedi.

2. Local Development:

   • Start the local development server using Firebase Emulator or deploy it to Firebase Functions for testing.
   • Use firebase serve (if using the Firebase CLI) to test locally.

3. Deployment:

   • Deploy your function to Firebase using firebase deploy and specify your project details in firebase.json.

Configuration

• Controllers: Add or modify controllers in the controllers directory, following the ThingController example for handling specific routes.
• Middleware: Implement custom middleware for global or route-specific functionality, ensuring they are registered in the Express application setup.
• Error Handling: Customize the CustomErrorHandler to manage how application errors are handled and responses are sent.

Security and Authentication

• Authorization Checker: The authorizationChecker function is a placeholder for implementing route-specific authorization logic.
• Current User Context: The currentUserChecker function demonstrates how to integrate user context into your controllers, potentially using session or token-based authentication.

Conclusion

This project template offers a streamlined approach to building serverless APIs with Firebase Functions, emphasizing simplicity, flexibility, and the effective use of routing-controllers and typedi. It's an excellent starting point for developers looking to create scalable, maintainable serverless applications without the overhead of more complex frameworks.