Middlewares
Middleware is a component in a web application that acts as an intermediary between the client request and the server response. In Flask, middleware is used to process requests before they reach the Flask application or after the application has processed the request but before sending the response back to the client.
Flask, being a lightweight and extensible framework, provides a way to implement middleware to perform additional processing, such as logging, authentication, input validation, error handling, or modifying requests and responses.
What is Middleware?
Middleware functions lie between the WSGI server (like Gunicorn or uWSGI) and the Flask application. They can:
- Inspect or modify incoming requests before they reach the Flask application.
- Inspect or modify outgoing responses before they are sent back to the client.
- Add additional functionality, such as logging or security headers.
Middleware Workflow
- The client sends a request.
- The middleware intercepts the request, processes it, and optionally modifies it.
- The request is forwarded to the Flask application.
- The Flask application processes the request and generates a response.
- The middleware intercepts the response, processes it, and optionally modifies it.
- The response is sent back to the client.
Types of Middleware in Flask
- Request Middleware: Runs before the Flask view function is called. It processes the incoming request.
- Response Middleware: Runs after the Flask view function generates a response. It processes the outgoing response.
Implementing Middleware in Flask
Flask does not have a built-in concept of middleware. However, middleware can be implemented in Flask using:
before_request
andafter_request
Hooks- WSGI Middleware
- Custom Middleware Classes