2. By using a `with` block, we make sure that the file-like object is closed after the generator function is done. So, after it finishes sending the response.
3. This `yield from` tells the function to iterate over that thing named `file_like`. And then, for each part iterated, yield that part as coming from this generator function (`iterfile`).

    So, it is a generator function that transfers the "generating" work to something else internally.

The `shutdown` would happen when you are **stopping** the application.

Maybe you need to start a new version, or you just got tired of running it. 🤷

///

### Lifespan function { #lifespan-function }

The first thing to notice, is that we are defining an async function with `yield`. This is very similar to Dependencies with `yield`.

{* ../../docs_src/events/tutorial003_py39.py hl[14:19] *}

     * Wait for the interrupting thread to set DONE. (See interruptTask().) We want to wait so that
     * the interrupting thread doesn't interrupt the _next_ thing to run on this thread.
     *
     * Note: We don't reset the interrupted bit, just wait for it to be set. If this is a thread
     * pool thread, the thread pool will reset it for us. Otherwise, the interrupted bit may have

# character that might be a shell metacharacter, then use eval to reverse
# that process (while maintaining the separation between arguments), and wrap
# the whole thing up as a single "set" statement.
#
# This will of course break if any of these variables contains a newline or
# an unmatched quote.
#

eval "set -- $(

MockWebServer
=============

A scriptable web server for testing HTTP clients


### Motivation

This library makes it easy to test that your app Does The Right Thing when it
makes HTTP and HTTPS calls. It lets you specify which responses to return and
then verify that requests were made as expected.

Because it exercises your full HTTP stack, you can be confident that you're

    }

    /**
     * Gets the cookie remember-me key for persistent login.
     * Currently returns empty as remember-me functionality is not enabled.
     *
     * @return an optional thing containing the remember-me key, or empty if not configured
     */
    @Override
    protected OptionalThing<String> getCookieRememberMeKey() {
        // example to use remember-me

  }

  companion object {
    @JvmOverloads
    fun body(
      hex: String,
      charset: String? = null,
    ): ResponseBody {
      val mediaType = if (charset == null) null else "any/thing; charset=$charset".toMediaType()
      return hex.decodeHex().toResponseBody(mediaType)
    }

    fun exhaust(reader: Reader): String {
      val builder = StringBuilder()
      val buf = CharArray(10)

This is something that you have to do yourself in your code, and make sure you use those JSON keys.

It's almost the only thing that you have to remember to do correctly yourself, to be compliant with the specifications.

For the rest, **FastAPI** handles it for you.

///

## Update the dependencies { #update-the-dependencies }

/// tip

The `callback_url` query parameter uses a Pydantic <a href="https://docs.pydantic.dev/latest/api/networks/" class="external-link" target="_blank">Url</a> type.

///

The only new thing is the `callbacks=invoices_callback_router.routes` as an argument to the *path operation decorator*. We'll see what that is next.

## Documenting the callback { #documenting-the-callback }

So, to avoid ID collisions, when creating the JWT token for the user, you could prefix the value of the `sub` key, e.g. with `username:`. So, in this example, the value of `sub` could have been: `username:johndoe`.

The important thing to keep in mind is that the `sub` key should have a unique identifier across the entire application, and it should be a string.

## Check it { #check-it }