Working with Request Parameters in aiohttp

When building web applications and APIs with aiohttp, accessing and validating request parameters is a common task. Parameters can be sent via the URL query string, form data, or JSON body. aiohttp provides easy ways to get at these values.

Accessing Request Parameters

The Request object in aiohttp contains the request details. The parameters can be accessed like:

url_params = request.query # query string params
form_data = await request.post() # form data
json_data = await request.json() # json body

The request.query returns a multi-dict, while request.post() and request.json() return awaitables that give access to form data and the JSON body.

Validating Parameters

For validation, aiohttp provides middleware that can check parameters before reaching route handlers:

from aiohttp import web

async def validate_params(app, handler):
    async def middleware(request):
        # Validate params
        # Raise HTTPBadRequest on issues
        
        return await handler(request)
    return middleware

app.router.add_get("/", handler, middlewares=[validate_params])

The middleware can check the parameter values and types, and raise HTTPBadRequest on errors before reaching the route.

Practical Examples

Some cases where parameter validation is useful:

Doing checks in middleware reduces code duplication and separates concerns.

Conclusion

aiohttp makes it easy to get request parameters. Adding validation middleware helps create robust APIs and catch issues early. Proper input validation reduces assumptions in route handlers.