Can you explain what middleware means in the context of FastAPI and how it is used?

In FastAPI, middleware is a component that intercepts HTTP requests and/or responses, allowing for additional processing before and after the request is handled by the endpoint function.

Middleware is used for tasks such as:

• Logging requests and responses
• Authentication and authorization
• Handling CORS
• Modifying or adding headers
• Error handling

Example of simple middleware in FastAPI:

from fastapi import FastAPI, Request

app = FastAPI()

@app.middleware("http")
async def simple_middleware(request: Request, call_next):
    print(f"Received request: {request.method} {request.url}")
    response = await call_next(request)
    response.headers["X-Custom-Header"] = "Value"
    return response

Here, the middleware logs request information and adds a custom header to the response. Middleware in FastAPI allows centralized management of application behavior at the request and response level.