// come close.
    USING_DECODER_WITH_SIZE_HINT {
      @Override
      String read(ByteSource byteSource, Charset cs) throws IOException {
        Optional<Long> size = byteSource.sizeIfKnown();
        // if we know the size and it fits in an int
        if (size.isPresent() && size.get().longValue() == size.get().intValue()) {
          // otherwise try to presize a StringBuilder

For that you need to access the request directly.

{* ../../docs_src/using_request_directly/tutorial001_py310.py hl[1,7:8] *}

By declaring a *path operation function* parameter with the type being the `Request` **FastAPI** will know to pass the `Request` in that parameter.

/// tip

Note that in this case, we are declaring a path parameter beside the request parameter.

## Pin your `fastapi` version { #pin-your-fastapi-version }

The first thing you should do is to "pin" the version of **FastAPI** you are using to the specific latest version that you know works correctly for your application.

For example, let's say you are using version `0.112.0` in your app.

If you use a `requirements.txt` file you could specify the version with:

```txt
fastapi[standard]==0.112.0

That documentation will show up in the Swagger UI at `/docs` in your API, and it will let external developers know how to build the *external API*.

This example doesn't implement the callback itself (that could be just a line of code), only the documentation part.

/// tip

The actual callback is just an HTTP request.

                }
            } else {
                /*
                 * NOTE: This is to provide a migration path for implementors of the legacy API which did not know about
                 * getLifecycles().
                 */

                String[] lifecycleIds = {"default", "clean", "site"};

                for (String lifecycleId : lifecycleIds) {

import okhttp3.OkHttpClient;
import okhttp3.Protocol;
import okhttp3.Request;
import okhttp3.Response;

/**
 * This prints events for a single in-flight call. It won't work for multiple concurrent calls
 * because we don't know what callStartNanos refers to.
 */
public final class PrintEventsNonConcurrent {
  private final OkHttpClient client = new OkHttpClient.Builder()
      .eventListener(new PrintingEventListener())
      .build();

When you mount a sub-application as described above, FastAPI will take care of communicating the mount path for the sub-application using a mechanism from the ASGI specification called a `root_path`.

That way, the sub-application will know to use that path prefix for the docs UI.

And the sub-application could also have its own mounted sub-applications and everything would work correctly, because FastAPI handles all these `root_path`s automatically.

```

---

If your application (somehow) doesn't have to communicate with anything else and wait for it to respond, use `async def`, even if you don't need to use `await` inside.

---

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.

      default:
        return new ImmutableEnumSet<>(set);
    }
  }

  /*
   * Notes on EnumSet and <E extends Enum<E>>:
   *
   * This class isn't an arbitrary ForwardingImmutableSet because we need to
   * know that calling {@code clone()} during deserialization will return an
   * object that no one else has a reference to, allowing us to guarantee
   * immutability. Hence, we support only {@link EnumSet}.
   */

+ Submit a ticket for your issue, assuming one does not already exist.
  + Clearly describe the issue, including steps to reproduce when it is a bug.
  + Make sure you fill in the earliest version that you know has the issue.
+ Fork the repository on GitHub.

Making and Submitting Changes
--------------

We accept Pull Requests via GitHub. The [developer mailing list][dev-ml-list] is the