rob-blackbourn / aiohttp-route-middleware

An extension for aiohttp which provides route local middleware

aiohttp-routed-middleware

Overview

An extension for aiohttp which provides route local middleware while remainining compatible with the existing router.

With the built in router the technique for managing route local middleware is to make nested applications. However nested applications require a unique url prefix. so the following cannot be achieved:

Request	Middleware	Handler
GET /post/{id}	authenticate, authorise(['post:read'])	get_post
POST /post/{id}	authenticate, authorise(['post:read:', 'post:write'])	create_post
DELETE /post/{id}	authenticate, authorise(['post:read:', 'post:write'])	delete_post

This router allows a chain of middleware terminated by a handler. For example:

post_app = web.Application(router=UrlDispatcherEx())
post_app.router.add_get('/{id}', authenticate, authorise(['post:read']), get_posts)
post_app.router.add_post('/{id}', authenticate, authorise(['post:read', 'post:write']), get_posts)
post_app.router.add_delete('/{id}', authenticate, authorise(['post:read', 'post:write']), get_posts)

app = web.Application()
app.add_subapp('/post', post_app)

Usage

Basic

A middleware function differs from a normal request handler, in that it gets given the next handler to call.

The following example shows how to add middleware to a route.

from aiohttp import web
from aiohttp_route_middleware import UrlDispatcherEx

app = web.Application(router=UrlDispatcherEx())

async def test(request):
    print("..entering handler")
    response = web.Response(text=f"extra_stuff=[{', '.join(request.extra_stuff)}]")
    print("..exiting handler")
    return response

@web.middleware
async def middleware1(request, handler):
    print("entering middleware 1")
    request.extra_stuff = ['foo']
    response = await handler(request)
    print("exiting middleware 1")
    return response

@web.middleware
async def middleware2(request, handler):
    print(".entering middleware 2")
    request.extra_stuff.append('bar')
    response = await handler(request)
    print(".exiting middleware 2")
    return response

app = web.Application(router=UrlDispatcherEx())
app.router.add_get('/', middleware1, middleware2, test)
web.run_app(app)

This would print out the following:

entering middleware 1
.entering middleware 2
..entering handler
..exiting handler
.exiting middleware 2
exiting middleware 1

Middleware failure

A middleware function may choose not to call the next handler; for example if there was an authentication error.

from aiohttp import web
from aiohttp_route_middleware import UrlDispatcherEx

async def test(request):
    return web.Response(text="Success")

@web.middleware
async def authenticate(request, handler):
    return web.Response(body="unauthenticated", status=401)

app = web.Application(router=UrlDispatcherEx())
app.router.add_get('/', authenticate, test)
web.run_app(app)

Installation

You can install it using pip:

pip install aiohttp-route-middleware

Details

The extension provides a router UrlDispatcherEx which extends from the built in class UrlDispatcher. The class can be used in the following manner:

from aiohttp_route_middleware import UrlDispatcherEx

...

app = web.Application(router=UrlDispatcherEx())

The extension allows multiple handlers to be specified. The handlers are called in order until a handler returns a non None response, at which point the response is returned and execution stops.

An example of this might be a route to update a comment on a post, The sequence might be:

1. Authenticate the user.
2. Check the user is authorised to post a comment.
3. Fetch the post.
4. Post the comment.

app.router.add_post('/comment?post_id=1234', authenticate, authorise, fetch_post, post_comment)

Each handler is written in the same manner as a normal handler, in that it takes a single request argument. The request argument may be modified or enriched by each handler.