Building Custom Middleware in FastAPI

Middleware in FastAPI acts as a powerful tool that sits between incoming requests and outgoing responses, allowing developers to add or modify functionalities without altering the core framework. FastAPI offers several built-in middleware components like CORS, TrustedHost, Session, and GZip, which address common API requirements. However, the true strength lies in creating custom middleware, which provides flexibility, reusability, code separation, and extensibility, enabling developers to tailor API behavior to specific use cases. This article explores the process of building custom middleware, both function-based and class-based, to modify requests and responses and implement features like rate limiting. It emphasizes the importance of middleware ordering, chaining, and testing to ensure robust API performance and security. Additionally, the article provides practical insights into middleware best practices, including performance optimization, security considerations, and the avoidance of common pitfalls, ultimately guiding developers in building efficient, scalable, and secure APIs with FastAPI.