// If the most recent read or write operation on the buffer was
// not a successful [Buffer.ReadRune], UnreadRune returns an error.  (In this regard
// it is stricter than [Buffer.UnreadByte], which will unread the last byte
// from any read operation.)
func (b *Buffer) UnreadRune() error {
	if b.lastRead <= opInvalid {
		return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune")
	}

        handler -->> client: HTTP-Error-Response
    end
    operation ->> client: Sendet Response an Client
    Note over client,operation: Response wurde gesendet, kann nicht mehr geändert werden
    opt Tasks
        operation -->> tasks: Sendet Hintergrundtasks
    end
    opt Löst andere Exception aus
        tasks -->> tasks: Handhabt Exception im Hintergrundtask-Code
    end
```

/// info

 */
@Experimental
public interface DependencyResolver extends Service {

    /**
     * Collects the transitive dependencies of some artifacts and builds a dependency graph for the given path scope.
     * Note that this operation is only concerned about determining the coordinates of the transitive dependencies and
     * does not actually resolve the artifact files.
     *
     * @param session the {@link Session}, must not be {@code null}

  protected UnmodifiableListIterator() {}

  /**
   * Guaranteed to throw an exception and leave the underlying data unmodified.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Unsupported operation.
   */
  @Deprecated
  @Override
  @DoNotCall("Always throws UnsupportedOperationException")
  public final void add(@ParametricNullness E e) {
    throw new UnsupportedOperationException();
  }

  /**

# Body - Fields

The same way you can declare additional validation and metadata in *path operation function* parameters with `Query`, `Path` and `Body`, you can declare validation and metadata inside of Pydantic models using Pydantic's `Field`.

## Import `Field`

First, you have to import it:

{* ../../docs_src/body_fields/tutorial001_an_py310.py hl[4] *}


/// warning

  // This field must only be set by the entity completing the attach
  // operation, i.e. the external-attacher.
  // +optional
  optional VolumeError attachError = 3;

  // detachError represents the last error encountered during detach operation, if any.
  // This field must only be set by the entity completing the detach
  // operation, i.e. the external-attacher.
  // +optional

		return
	}

	// Validate operation
	operation := mux.Vars(r)["operation"]
	if operation != "attach" && operation != "detach" {
		writeErrorResponseJSON(ctx, w, errorCodes.ToAPIErr(ErrAdminInvalidArgument), r.URL)
		return
	}

	isAttach := operation == "attach"

	// Validate API arguments in body.
	password := cred.SecretKey

///

```Python hl_lines="22"
{!> ../../docs_src/dependencies/tutorial005.py!}
```

////

/// info

Notice that we are only declaring one dependency in the *path operation function*, the `query_or_cookie_extractor`.

But **FastAPI** will know that it has to solve `query_extractor` first, to pass the results of that to `query_or_cookie_extractor` while calling it.

///

```mermaid

  override fun checkClientTrusted(
    chain: Array<out X509Certificate>,
    authType: String?,
  ) = throw CertificateException("Unsupported operation")

  override fun checkServerTrusted(
    chain: Array<out X509Certificate>,
    authType: String,
  ) = throw CertificateException("Unsupported operation")

## Use the `Request` object directly

Let's imagine you want to get the client's IP address/host inside of your *path operation function*.

For that you need to access the request directly.

```Python hl_lines="1  7-8"
{!../../docs_src/using_request_directly/tutorial001.py!}
```

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

/// tip