Python ASGI Middleware

Usage Introduction

On making custom Middleware, we use starlette middleware abstract class BaseHTTPMiddleware. To implement a middleware class using BaseHTTPMiddleware, you must override the async def dispatch(request, call_next) method.

Example

Overriding async def dispatch(request, call_next) method.

class CustomHeaderMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request, call_next):
        response = await call_next(request)
        response.headers['Custom'] = 'Example'
        return response

Add more configuration options (optional)

class CustomHeaderMiddleware(BaseHTTPMiddleware):
    def __init__(self, app, header_value='Example'):
        super().__init__(app)
        self.header_value = header_value

    async def dispatch(self, request, call_next):
        response = await call_next(request)
        response.headers['Custom'] = 'Example'
        return response

Then we include the middleware to Starlette application instance.

middleware = [
    Middleware(CustomHeaderMiddleware)
]

app = Starlette(routes=routes, middleware=middleware)

Then we include the middleware to FastAPI application instance.


from fastapi import FastAPI

app = FastAPI()

app.add_middleware(CustomHeaderMiddleware, header_value='custom_header')

Another way to use middleware for FastAPI.

import time

from fastapi import FastAPI, Request

app = FastAPI()


@app.middleware("http")
async def add_process_time_header(request: Request, call_next):
    start_time = time.time()
    response = await call_next(request)
    process_time = time.time() - start_time
    response.headers["X-Process-Time"] = str(process_time)
    return response

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