#### Operation

"Operation" here refers to one of the HTTP "methods".

One of:

* `POST`
* `GET`
* `PUT`
* `DELETE`

...and the more exotic ones:

* `OPTIONS`
* `HEAD`
* `PATCH`
* `TRACE`

In the HTTP protocol, you can communicate to each path using one (or more) of these "methods".

---

In short:

* `100` and above are for "Information". You rarely use them directly.  Responses with these status codes cannot have a body.
* **`200`** and above are for "Successful" responses. These are the ones you would use the most.
    * `200` is the default status code, which means everything was "OK".
    * Another example would be `201`, "Created". It is commonly used after creating a new record in the database.

import java.io.PrintWriter;

import org.apache.maven.api.annotations.Nullable;
import org.apache.maven.api.cli.Logger;

/**
 * Proto {@link Logger}. Uses provided {@link PrintStream}s or {@link System} ones as fallback.
 * Supports only two levels: ERROR and WARNING, that is emitted to STDERR and STDOUT.
 */
public class ProtoLogger implements Logger {

    private final PrintWriter out;
    private final PrintWriter err;

                This is much simpler (less smart) than `response_model_exclude_unset`
                and `response_model_exclude_defaults`. You probably want to use one of
                those two instead of this one, as those allow returning `None` values
                when it makes sense.

                Read more about it in the

## Documenting the callback

The actual callback code will depend heavily on your own API app.

And it will probably vary a lot from one app to the next.

It could be just one or two lines of code, like:

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
httpx.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

In this case, it would be better to get **one extra server** and run some processes on it so that they all have **enough RAM and CPU time**.

It will all be combined and included in your OpenAPI, and shown in the API docs:

<img src="/img/tutorial/additional-responses/image01.png">

## Combine predefined responses and custom ones

You might want to have some predefined responses that apply to many *path operations*, but you want to combine them with custom responses needed by each *path operation*.

     * if any. Hence, the list returned by this method depends on which lifecycle step of the build was it invoked.
     * The head of returned list is result of {@link Project#getArtifacts()} method, so same applies here: the list can have
     * minimum of one element. The maximum number of elements is in turn dependent on build configuration and lifecycle

But we also pass a `list` of scopes, in this case with just one scope: `items` (it could have more).

And the dependency function `get_current_active_user` can also declare sub-dependencies, not only with `Depends` but also with `Security`. Declaring its own sub-dependency function (`get_current_user`), and more scope requirements.

In this case, it requires the scope `me` (it could require more than one scope).

/// note

The fast food store has 8 processors (cashiers/cooks). While the concurrent burgers store might have had only 2 (one cashier and one cook).

But still, the final experience is not the best. 😞

---

This would be the parallel equivalent story for burgers. 🍔

For a more "real life" example of this, imagine a bank.