{* ../../docs_src/custom_response/tutorial004.py hl[7,21,23] *}

In this example, the function `generate_html_response()` already generates and returns a `Response` instead of returning the HTML in a `str`.

By returning the result of calling `generate_html_response()`, you are already returning a `Response` that will override the default **FastAPI** behavior.

FastAPI will use this return type to:

* **Validate** the returned data.
    * If the data is invalid (e.g. you are missing a field), it means that *your* app code is broken, not returning what it should, and it will return a server error instead of returning incorrect data. This way you and your clients can be certain that they will receive the data and the data shape expected.
* Add a **JSON Schema** for the response, in the OpenAPI *path operation*.

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.

You can also declare the `Response` parameter in dependencies, and set cookies (and headers) in them.

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

You can also create cookies when returning a `Response` directly in your code.

To do that, you can create a response as described in [Return a Response Directly](response-directly.md){.internal-link target=_blank}.

Then set Cookies in it, and then return it:

**FastAPI** provides the same `starlette.responses` as `fastapi.responses` just as a convenience for you, the developer. But most of the available responses come directly from Starlette.

///

## Returning a custom `Response` { #returning-a-custom-response }

5. You can use other standard type annotations with dataclasses as the request body.

    In this case, it's a list of `Item` dataclasses.

6. Here we are returning a dictionary that contains `items` which is a list of dataclasses.

    FastAPI is still capable of <abbr title="converting the data to a format that can be transmitted">serializing</abbr> the data to JSON.

// reduceReadQuorumErrs behaves like reduceErrs but only for returning
// values of maximally occurring errors validated against readQuorum.
func reduceReadQuorumErrs(ctx context.Context, errs []error, ignoredErrs []error, readQuorum int) (maxErr error) {
	return reduceQuorumErrs(ctx, errs, ignoredErrs, readQuorum, errErasureReadQuorum)
}

// reduceWriteQuorumErrs behaves like reduceErrs but only for returning

	b.mu.Lock()
	defer b.mu.Unlock()

	// Check if exists already.
	if c, ok := b.caches[o.ID]; ok {
		c.lastHandout = time.Now()
		b.caches[o.ID] = c
		b.debugf("returning existing %v", o.ID)
		return c
	}

	if !o.Create {
		return metacache{
			id:     o.ID,
			bucket: o.Bucket,
			status: scanStateNone,
		}
	}

	// Create new and add.

It will use the default status code or the one you set in your *path operation*.

## Additional status codes { #additional-status-codes_1 }

If you want to return additional status codes apart from the main one, you can do that by returning a `Response` directly, like a `JSONResponse`, and set the additional status code directly.

        assertNotNull(provider1);
        assertNotNull(provider2);
        assertNotSame(provider1, provider2);
    }

    // Test with config returning null time adjustment
    public void test_nullTimeAdjustment() {
        FessConfig nullAdjustConfig = new FessConfig.SimpleImpl() {
            private static final long serialVersionUID = 1L;

            @Override