Limitations¶

The adapter is a thin bridge, therefore some aiohttp and ASGI mechanisms need attention.

The resource takes no prefix from aiohttp¶

ASGIResource.add_prefix() raises NotImplementedError, therefore Application.add_subapp() does not accept an application which holds the resource:

subapp = web.Application()
subapp.router.register_resource(ASGIResource(asgi_app))

# NotImplementedError
aiohttp_app.add_subapp("/sub", subapp)

Use the root_path argument of the resource instead of a subapp prefix:

aiohttp_app.router.register_resource(
    ASGIResource(asgi_app, root_path="/sub"),
)

Application.add_domain() works, because it gives no prefix to the resources.

A catch-all resource changes the registration order¶

With the default root_path="/" the resource accepts every path. aiohttp reuses the last added resource when its raw_match() accepts the path, therefore a router.add_get() call after such a resource raises AttributeError: 'ASGIResource' object has no attribute 'add_route'. Add the aiohttp routes before the resource, or give the resource a prefix. See Hybrid application.

The command line server sends no lifespan events¶

The aiohttp-asgi command serves the requests, but it does not send lifespan.startup and lifespan.shutdown. An application which needs those events runs through an aiohttp application with lifespan_mount().

The resource gives no routes to aiohttp¶

The resource reports no routes, so len(resource) is zero and the iteration over it gives nothing. get_info() raises NotImplementedError, and url_for() returns the root_path. The aiohttp tools which list the routes, for example a route table in a debug page, therefore show no ASGI route.

Worker processes need fork¶

The -w/--workers option of the command needs fork and forklib, so it exists on POSIX systems only. Windows runs one process.

The ASGI extensions are not implemented¶

The adapter speaks the HTTP and the WebSocket part of the ASGI specification. The scope holds no extensions key, therefore an application which needs an extension, for example http.response.push or a path send extension, gets no answer for it.

The deprecated set_current_app()¶

ASGIMatchInfo.set_current_app() is deprecated. Use add_app(), which the aiohttp application does itself.

Versions¶

Python 3.9 or later.
aiohttp 3.x. The adapter uses the match info and the resource interfaces of that series.