# OpenAPI Webhooks

There are cases where you want to tell your API **users** that your app could call *their* app (sending a request) with some data, normally to **notify** of some type of **event**.

This means that instead of the normal process of your users sending requests to your API, it's **your API** (or your app) that could **send requests to their system** (to their API, their app).

This is normally called a **webhook**.

## Webhooks steps

Asynchronous code just means that the language 💬 has a way to tell the computer / program 🤖 that at some point in the code, it 🤖 will have to wait for *something else* to finish somewhere else. Let's say that *something else* is called "slow-file" 📝.

So, during that time, the computer can go and do some other work, while "slow-file" 📝 finishes.

```

### `HTMLResponse`

Takes some text or bytes and returns an HTML response, as you read above.

### `PlainTextResponse`

Takes some text or bytes and returns an plain text response.

```Python hl_lines="2  7  9"
{!../../../docs_src/custom_response/tutorial005.py!}
```

### `JSONResponse`

Takes some data and returns an `application/json` encoded response.

* Each application that you have running on your computer has some process behind it, each running program, each window, etc. And there are normally many processes running **at the same time** while a computer is on.
* There can be **multiple processes** of the **same program** running at the same time.

And these same full-stack generators were the base of the [**FastAPI** Project Generators](project-generation.md){.internal-link target=_blank}.

!!! info
    Flask-apispec was created by the same Marshmallow developers.

!!! check "Inspired **FastAPI** to"
    Generate the OpenAPI schema automatically, from the same code that defines serialization and validation.

Then your API will (let's imagine):

* Send the invoice to some customer of the external developer.
* Collect the money.
* Send a notification back to the API user (the external developer).
    * This will be done by sending a POST request (from *your API*) to some *external API* provided by that external developer (this is the "callback").

## The normal **FastAPI** app

        name = "CHECK_CLEAN_M2_ANDROID_USER_HOME"
        executionMode = BuildStep.ExecutionMode.ALWAYS
        scriptContent = if (os == Os.WINDOWS) {
            checkCleanDirWindows("%teamcity.agent.jvm.user.home%\\.m2\\repository") +
                checkCleanDirWindows("%teamcity.agent.jvm.user.home%\\.m2\\.gradle-enterprise") +
                checkCleanDirWindows("%teamcity.agent.jvm.user.home%\\.m2\\.develocity") +

## Client and SDK Generators - Sponsor

There are also some **company-backed** Client and SDK generators based on OpenAPI (FastAPI), in some cases they can offer you **additional features** on top of high-quality generated SDKs/clients.

          approvals: 2

# To simplify the automations section, some calculations are placed under unique YAML keys defined here.
# Read the "|" not as "or", but as a "pipe", taking the output of the previous command and passing it to the next command.
# This section could also appear ahead of the automations section.

            )
        }
    }

    @Test
    fun `should fail if some method was upgraded but it was not actually changed`() {
        checkBinaryCompatibleFailsWithoutReport(
            v1 = {
                withFile(
                    "java/com/example/Task.java",