Middleware

Middleware is a chain of functions terminated by a callback.

It can be used to add content to the request and response or to control the calling of subsequent handlers.

A middleware callback is an async function with the following prototype.

response = await fn(request)

This is the same as an HTTP handler, with the addition of the callback which is either another middleware callback or an HTTP handler.

Simple Example

Here is a simple middleware example.

import uvicorn
from bareasgi import Application, text_writer

async def first_middleware(request, handler):
    request.context['message'] = 'This is first the middleware. '
    response = await handler(request)
    return response


async def second_middleware(request, handler):
    request.context['message'] += 'This is the second middleware.'
    response = await handler(request)
    return response


async def http_request_callback(request):
    return HttpResponse(200, [(b'content-type', b'text/plain')], text_writer(request.context['message']))


app = Application(middlewares=[first_middleware, second_middleware])
app.http_router.add({'GET'}, '/test', http_request_callback)

uvicorn.run(app, port=9009)