## Adding ASGI middlewares { #adding-asgi-middlewares }

As **FastAPI** is based on Starlette and implements the <abbr title="Asynchronous Server Gateway Interface">ASGI</abbr> specification, you can use any ASGI middleware.

A middleware doesn't have to be made for FastAPI or Starlette to work, as long as it follows the ASGI spec.

## ASGI Servers { #asgi-servers }

Let's go a little deeper into the details.

FastAPI uses a standard for building Python web frameworks and servers called <abbr title="Asynchronous Server Gateway Interface">ASGI</abbr>. FastAPI is an ASGI web framework.

* <a href="https://tartiflette.io/" class="external-link" target="_blank">Tartiflette</a>
    * With <a href="https://tartiflette.github.io/tartiflette-asgi/" class="external-link" target="_blank">Tartiflette ASGI</a> to provide ASGI integration
* <a href="https://graphene-python.org/" class="external-link" target="_blank">Graphene</a>

/// warning

If your application relies on lifespan events, the `AsyncClient` won't trigger these events. To ensure they are triggered, use `LifespanManager` from <a href="https://github.com/florimondmanca/asgi-lifespan#usage" class="external-link" target="_blank">florimondmanca/asgi-lifespan</a>.

///

## Other Asynchronous Function Calls { #other-asynchronous-function-calls }

## Technical Details { #technical-details }

Just a technical detail for the curious nerds. 🤓

Underneath, in the ASGI technical specification, this is part of the <a href="https://asgi.readthedocs.io/en/latest/specs/lifespan.html" class="external-link" target="_blank">Lifespan Protocol</a>, and it defines events called `startup` and `shutdown`.

/// info

/// note | Technical Details

ASGI is a new "standard" being developed by Django core team members. It is still not a "Python standard" (a PEP), although they are in the process of doing that.

Nevertheless, it is already being used as a "standard" by several tools. This greatly improves interoperability, as you could switch Uvicorn for any other ASGI server (like Daphne or Hypercorn), or you could add ASGI compatible tools, like `python-socketio`.

### Technical Details: `root_path` { #technical-details-root-path }

When you mount a sub-application as described above, FastAPI will take care of communicating the mount path for the sub-application using a mechanism from the ASGI specification called a `root_path`.

That way, the sub-application will know to use that path prefix for the docs UI.

The simpler the problem solved by the tool, the better performance it will get. And most of the benchmarks don't test the additional features provided by the tool.

The hierarchy is like:

* **Uvicorn**: an ASGI server
    * **Starlette**: (uses Uvicorn) a web microframework
        * **FastAPI**: (uses Starlette) an API microframework with several additional features for building APIs, with data validation, etc.

* **Uvicorn**:

/// note | Technical Details

The ASGI specification defines a `root_path` for this use case.

And the `--root-path` command line option provides that `root_path`.

///

### Checking the current `root_path` { #checking-the-current-root-path }

You can get the current `root_path` used by your application for each request, it is part of the `scope` dictionary (that's part of the ASGI spec).

For production you would use `fastapi run` instead. 🚀

Internally, **FastAPI CLI** uses <a href="https://www.uvicorn.org" class="external-link" target="_blank">Uvicorn</a>, a high-performance, production-ready, ASGI server. 😎

## `fastapi dev` { #fastapi-dev }

Running `fastapi dev` initiates development mode.