Middlewares¶

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In this section, you'll learn how middleware works in Ravyn and how to add your own.

What is middleware?¶

Middleware is ASGI code that runs around request handling.

Common uses:

Logging.
Authentication.
Compression.
Security headers.
Cross-cutting validation.

Adding middleware¶

Use DefineMiddleware and pass middleware classes in Ravyn(..., middleware=[...]).

from lilya.middleware import DefineMiddleware
from lilya.types import ASGIApp, Receive, Scope, Send
from ravyn import Gateway, Ravyn, get


class LogMiddleware:
    def __init__(self, app: ASGIApp):
        self.app = app

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        if scope["type"] == "http":
            print(f"{scope['method']} {scope['path']}")
        await self.app(scope, receive, send)


@get("/")
async def home() -> dict:
    return {"hello": "world"}


app = Ravyn(
    routes=[Gateway(handler=home)],
    middleware=[DefineMiddleware(LogMiddleware)],
)

Built-in middleware examples¶

CORS¶

from ravyn import CORSConfig, Ravyn

app = Ravyn(
    routes=[],
    cors_config=CORSConfig(
        allow_origins=["*"],
        allow_methods=["*"],
        allow_headers=["*"],
    ),
)

Trusted host¶

from lilya.middleware import DefineMiddleware
from ravyn import Ravyn
from ravyn.middleware import TrustedHostMiddleware

app = Ravyn(
    routes=[],
    middleware=[DefineMiddleware(TrustedHostMiddleware, allowed_hosts=["example.com", "localhost"])],
)

Middleware order¶

Middleware executes in declaration order from outermost to innermost.

middleware=[DefineMiddleware(A), DefineMiddleware(B)]

Execution order:

A before request.
B before request.
Handler.
B after handler.
A after handler.

Next step¶

Continue to background tasks.