The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

{* ../../docs_src/dependencies/tutorial013_an_py310.py ln[19:21] *}

...would be run after the response finishes sending the slow data:

{* ../../docs_src/dependencies/tutorial013_an_py310.py ln[30:38] hl[31:33] *}

But as `generate_stream()` doesn't use the database session, it is not really necessary to keep the session open while sending the response.

* It's running without any authentication, it doesn't have to send any credentials.
* The browser thinks it's not sending JSON (because of the missing `Content-Type` header).

Then the malicious website could make the local AI agent send angry messages to the user's ex-boss... or worse. 😅

## Open Internet { #open-internet }

## Raw Data { #raw-data }

If you need to send data **without** JSON encoding, use `raw_data` instead of `data`.

This is useful for sending pre-formatted text, log lines, or special <dfn title="A value used to indicate a special condition or state">"sentinel"</dfn> values like `[DONE]`.

{* ../../docs_src/server_sent_events/tutorial003_py310.py hl[17] *}

/// note

```console
$ pip install python-multipart
```

This is because **OAuth2** uses "form data" for sending the `username` and `password`.

///

Run the example with:

<div class="termy">

```console
$ fastapi dev

  }

  override fun flushRequest() {
    socket.sink.flush()
  }

  override fun finishRequest() {
    socket.sink.flush()
  }

  /** Returns bytes of a request header for sending on an HTTP transport. */
  fun writeRequest(
    headers: Headers,
    requestLine: String,
  ) {
    check(state == STATE_IDLE) { "state: $state" }
    socket.sink.writeUtf8(requestLine).writeUtf8("\r\n")

the server (the machine, host, etc.) and **managing all the HTTPS parts**: receiving the **encrypted HTTPS requests**, sending the **decrypted HTTP requests** to the actual HTTP application running in the same server (the **FastAPI** application, in this case), take the **HTTP response** from the application, **encrypt it** using the appropriate **HTTPS certificate** and sending it back to the client using **HTTPS**. This server is often called a **[TLS Termination Proxy](https://en.wikipedia.or...

    } catch (e: IOException) {
      failConnection(e)
    }
  }

  /** For testing: sends a ping and waits for a pong. */
  @Throws(InterruptedException::class)
  fun writePingAndAwaitPong() {
    writePing()
    awaitPong()
  }

  /** For testing: sends a ping to be awaited with [awaitPong]. */
  @Throws(InterruptedException::class)
  fun writePing() {
    withLock {

This includes, for example:

* Email notifications sent after performing an action:
    * As connecting to an email server and sending an email tends to be "slow" (several seconds), you can return the response right away and send the email notification in the background.
* Processing data:

## Base64 vs Files { #base64-vs-files }

Consider first if you can use [Request Files](../tutorial/request-files.md) for uploading binary data and [Custom Response - FileResponse](./custom-response.md#fileresponse--fileresponse-) for sending binary data, instead of encoding it in JSON.

JSON can only contain UTF-8 encoded strings, so it can't contain raw bytes.