# Middleware { #middleware }

You can add middleware to **FastAPI** applications.

A "middleware" is a function that works with every **request** before it is processed by any specific *path operation*. And also with every **response** before returning it.

* It takes each **request** that comes to your application.
* It can then do something to that **request** or run any needed code.

These are the exceptions that you can raise to show errors to the client.

When you raise an exception, as would happen with normal Python, the rest of the execution is aborted. This way you can raise these exceptions from anywhere in the code to abort a request and show the error to the client.

You can use:

* `HTTPException`
* `WebSocketException`

These exceptions can be imported directly from `fastapi`:

```python

But you can return a `JSONResponse` directly from your *path operations*.

It might be useful, for example, to return custom headers or cookies.

## Return a `Response` { #return-a-response }

In fact, you can return any `Response` or any sub-class of it.

/// tip

`JSONResponse` itself is a sub-class of `Response`.

///

# Body - Fields { #body-fields }

The same way you can declare additional validation and metadata in *path operation function* parameters with `Query`, `Path` and `Body`, you can declare validation and metadata inside of Pydantic models using Pydantic's `Field`.

## Import `Field` { #import-field }

First, you have to import it:

{* ../../docs_src/body_fields/tutorial001_an_py310.py hl[4] *}


/// warning

# Background Tasks - `BackgroundTasks`

You can declare a parameter in a *path operation function* or dependency function with the type `BackgroundTasks`, and then you can use it to schedule the execution of background tasks after the response is sent.

You can import it directly from `fastapi`:

```python
from fastapi import BackgroundTasks
```

```

The command deploys MinIO on the Kubernetes cluster in the default configuration. The [configuration](#configuration) section lists the parameters that can be configured during installation.

### Installing the Chart (toy-setup)

Minimal toy setup for testing purposes can be deployed using:

```bash

# Templates { #templates }

You can use any template engine you want with **FastAPI**.

A common choice is Jinja2, the same one used by Flask and other tools.

There are utilities to configure it easily that you can use directly in your **FastAPI** application (provided by Starlette).

## Install dependencies { #install-dependencies }

<%@page pageEncoding="UTF-8" contentType="text/html; charset=UTF-8"%>
<h2>Query Syntax</h2>
<dl>
	<dt>Field</dt>
	<dd>
		You can search any field by typing the field name followed by a colon
		":" and then the term you are looking for. If you want to find
		documents which has "Fess" as the document title, you can enter:
		<pre>title:Fess</pre>
		The available fields are "url", "host", "site", "title", "content",

# Sub-dependencies { #sub-dependencies }

You can create dependencies that have **sub-dependencies**.

They can be as **deep** as you need them to be.

**FastAPI** will take care of solving them.

## First dependency "dependable" { #first-dependency-dependable }

You could create a first dependency ("dependable") like:

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[8:9] *}

The key ID is `E2F38302C8075E3D` and its fingerprint is `1BD97A6A154E7810EE0BC832E2F38302C8075E3D`.
You can also find the key in the [Gradle website](https://gradle.org/keys/) and on [public key servers](https://keys.openpgp.org/search?q=maven-publishing%40gradle.com).

## Verification instructions

### Importing the key

You can import the key into your GPG keyring in one of two ways.