Python Falcon – Middleware

Middleware in Falcon is a powerful mechanism that allows you to preprocess requests and post-process responses globally across your application. It acts as a bridge between incoming and outgoing requests, allowing you to perform authentication, logging, and request/response modification tasks.

What is Python Falcon – Middleware?

Middleware in Python Falcon is a critical component for intercepting and altering incoming requests and outgoing responses within web applications. It links the server and the application logic, allowing developers to preprocess requests and post-process responses in a global context. The fundamental technique for constructing middleware in Falcon is to define classes with appropriate event handler methods. These methods are used at various phases of request and response processing, giving developers fine-grained control over request lifecycle management.

Python Falcon – Middleware

In Falcon, middleware is implemented as classes that define various event handler methods. These methods are executed at different stages of request and response processing.

• WSGI Middleware methods
• ASGI Middleware methods

Python Falcon – WSGI Middleware Methods

WSGI Middleware Methods are pivotal for processing incoming requests and responses in a WSGI application. The process_request() method facilitates preprocessing tasks before routing the request to a specific resource or endpoint, enabling modifications or validation. Similarly, the process_resource() method handles the request after routing, providing an opportunity for further processing or validation based on the resource being accessed. .

File Structure

--project
            -app.py
            -middleware.py
            -resources.py

app.py : In this example, below Python code sets up a Falcon application, a lightweight framework for building RESTful APIs, with middleware and a sample resource. It then configures a WSGI server to run the Falcon app on localhost, port 8000, continuously serving incoming HTTP requests.

Python3

import falcon
from wsgiref import simple_server
from middleware import SampleWSGIMiddleware
from resources import SampleResource

# Create a Falcon App instance and add middleware
app = falcon.App(middleware=SampleWSGIMiddleware())

# Add the resource to the Falcon API
app.add_route('/', SampleResource())

# Run the Falcon application
if __name__ == '__main__':
    # Create a WSGI server instance
    httpd = simple_server.make_server('127.0.0.1', 8000, app)

    # Start the server
    print('Falcon server starting on port 8000...')
    httpd.serve_forever()

middleware.py : below Python code sets up a Falcon web API using Falcon framework. It imports necessary modules, including Falcon itself, sets up middleware, defines a resource, creates an instance of the Falcon application, adds a route for the defined resource, creates a WSGI server instance.

Python3

class SampleWSGIMiddleware:
    def process_request(self, req, resp):
        print("Processing request...")
        # Modify request object if needed

    def process_resource(self, req, resp, resource, params):
        print("Processing resource...")
        # Modify request and response objects if needed

    def process_response(self, req, resp, resource, req_succeeded):
        print("Processing response...")
        # Modify response object if needed

resources.py: Below, code defines a Falcon resource class `SampleResource` with an `on_get` method to handle GET requests, responding with a “Hello, WSGI Falcon Middleware!” message.

Python3

import falcon


class SampleResource:
    def on_get(self, req, resp):
        resp.status = falcon.HTTP_200
        resp.body = "Hello, WSGI Falcon Middleware!"

Output

Hello, WSGI Falcon Middleware!

Python Falcon – ASGI Middleware Methods

ASGI Middleware Methods serve to manage the initialization and shutdown processes of an ASGI application. The process_startup() method handles the startup event, allowing for the initialization of necessary resources or connections. Conversely, the process_shutdown() method manages the shutdown event, ensuring graceful termination by releasing resources or closing connections.

File structure

--project
            -app.py
            -middleware.py
            -resources.py

app.py : Below, Python code sets up a Falcon web API using the Falcon framework. It imports necessary modules, defines a Falcon application instance, adds middleware (`SampleASGIMiddleware`) to handle requests, adds a route for a resource (`SampleResource`), creates a WSGI server instance listening on port 8000.

Python3

import falcon
from wsgiref import simple_server
from middleware import SampleASGIMiddleware
from resources import SampleResource

# Create a Falcon App instance
app = falcon.App()

# Add middleware to the aFalcon App
app.req_options.middleware.append(SampleASGIMiddleware())

# Add the resource to the Falcon API
app.add_route('/', SampleResource())

# Run the Falcon application
if __name__ == '__main__':
    # Create a WSGI server instance
    httpd = simple_server.make_server('127.0.0.1', 8000, app)

    # Start the server
    print('Falcon server starting on port 8000...')
    httpd.serve_forever()

middleware.py: below Python class, SampleASGIMiddleware, defines two asynchronous methods: process_request and process_response. The former is called before passing the request to the application, while the latter is called after generating the response.

Python3

class SampleASGIMiddleware:
    async def process_request(self, req, resp):
        print("Processing request...")
        # Modify request object if needed

    async def process_response(self, req, resp, resource, req_succeeded):
        print("Processing response...")
        # Modify response object if needed

resources.py : below code defines a Falcon resource class `SampleResource` with an asynchronous `on_get` method to handle GET requests, responding with a “Hello, ASGI Falcon Middleware!” message.

Python3

import falcon

class SampleResource:
    async def on_get(self, req, resp):
        resp.status = falcon.HTTP_200
        resp.body = "Hello, ASGI Falcon Middleware!

Output

Hello, ASGI Falcon Middleware!

Conclusion

In conclusion, middleware in Python Falcon is a critical component for intercepting and processing requests and answers within Falcon applications. Middleware enables developers to implement numerous preprocessing and postprocessing functions like as authentication, logging, and request/response modification in a modular and reusable manner. Understanding the various middleware technologies, such as WSGI and ASGI, allows developers to improve the functionality.