Working with Middlewares and Events

As Batman's application grew more complex, Robyn taught him about middlewares, startup and shutdown events, and even working with WebSockets. Batman learned how to create functions that could execute before or after a request, manage the application's life cycle, and handle real-time communication with clients using WebSockets.

Handling Events

Batman discovered that he could add startup and shutdown events to manage his application's life cycle. He added the following code to define these events:

Batman was excited to learn that he could add events as functions as well as decorators.

Request

GET

/hello_world

async def startup_handler():
  print("Starting up")

app.startup_handler(startup_handler)

For an asynchronous request, Batman used:

Request

GET

/hello_world

@app.get("/")
async def h(request):
    return "Hello, world"

POST/http_requests

Handling Middlewares

Batman learned to use both sync and async functions for middlewares. He wrote the following code to add a middleware that would execute before and after each request. A before request middleware is a function that executes before each request. It can modify the request object or perform any other operation before the request is processed. An after request middleware is a function that executes after each request. It can modify the response object or perform any other operation after the request is processed.

Every before request middleware should accept a request object and return a request object. Every after request middleware should accept a response object and return a response object on happy case scenario.

The execution of the before request middleware is stopped if any of the before request middleware returns a response object. The response object is returned to the client without executing the after request middleware or the main entry point code.

Request

POST

/http_requests

@app.before_request("/")
async def hello_before_request(request: Request):
    request.headers["before"] = "sync_before_request"
    return request

@app.after_request("/")
def hello_after_request(response: Response):
    response.headers.set("after", "sync_after_request"")
    return response

What's next?

Robyn - Great, you're now familiar with the certain advanced concepts of Robyn. Middlewares serve the base of

Batman - "Authentication! I want to learn about authentication. I want to make sure that only the right people can access my application."

Robyn - Yes, Authentication!

Authentication