If you just don't know, use normal `def`.

---

**Note**: You can mix `def` and `async def` in your *path operation functions* as much as you need and define each one using the best option for you. FastAPI will do the right thing with them.

Anyway, in any of the cases above, FastAPI will still work asynchronously and be extremely fast.

But by following the steps above, it will be able to do some performance optimizations.

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 }

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)

  private final long totalLoadTime;

  private final long evictionCount;

  /**
   * Constructs a new {@code CacheStats} instance.
   *
   * <p>Five parameters of the same type in a row is a bad thing, but this class is not constructed
   * by end users and is too fine-grained for a builder.
   */
  @SuppressWarnings("GoodTime") // should accept a java.time.Duration
  public CacheStats(
      long hitCount,

  private final long totalLoadTime;

  private final long evictionCount;

  /**
   * Constructs a new {@code CacheStats} instance.
   *
   * <p>Five parameters of the same type in a row is a bad thing, but this class is not constructed
   * by end users and is too fine-grained for a builder.
   */
  @SuppressWarnings("GoodTime") // should accept a java.time.Duration
  public CacheStats(
      long hitCount,

        }
        sessionBuilder.setProxySelector(proxySelector);

        // Note: we do NOT use WagonTransportConfigurationKeys here as Maven Core does NOT depend on Wagon Transport
        // and this is okay and "good thing".
        DefaultAuthenticationSelector authSelector = new DefaultAuthenticationSelector();
        for (Server server : request.getServers()) {
            AuthenticationBuilder authBuilder = new AuthenticationBuilder();

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 }

/// 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 }