return errCode
	}

	clientETag, err := etag.FromContentMD5(r.Header)
	if err != nil {
		return ErrInvalidDigest
	}

	// Extract either 'X-Amz-Content-Sha256' header or 'X-Amz-Content-Sha256' query parameter (if V4 presigned)
	// Do not verify 'X-Amz-Content-Sha256' if skipSHA256.
	var contentSHA256 []byte
	if skipSHA256 := skipContentSha256Cksum(r); !skipSHA256 && isRequestPresignedSignatureV4(r) {

   * by applying the given {@code AsyncFunction} to the result of the original {@code Future}.
   * Example usage:
   *
   * {@snippet :
   * FluentFuture<RowKey> rowKeyFuture = FluentFuture.from(indexService.lookUp(query));
   * ListenableFuture<QueryResult> queryFuture =
   *     rowKeyFuture.transformAsync(dataService::readFuture, executor);
   * }
   *

		}
	}

	// Parse date header.
	var err error
	date, err = time.Parse(iso8601Format, dateStr)
	if err != nil {
		return cred, "", "", time.Time{}, ErrMalformedDate
	}

	// Query string.
	queryStr := req.Form.Encode()

	// Get canonical request.
	canonicalRequest := getCanonicalRequest(extractedSignedHeaders, payload, queryStr, req.URL.Path, req.Method)

    }

    @Override
    public void add(@ParametricNullness V value) {
      previous = addNode(key, value, next);
      nextIndex++;
      current = null;
    }
  }

  // Query Operations

  @Override
  public int size() {
    return size;
  }

  @Override
  public boolean isEmpty() {
    return head == null;
  }

  @Override

O `Union` em `Union[str, None]` não é utilizado pelo FastAPI, mas permite ao seu editor de texto lhe dar um suporte melhor e detectar erros.

///

## Sem o Pydantic

    // Try the same server first
    InetAddress serverAddress = transport.getRemoteAddress();
    
    if (isWitnessServiceAvailable(serverAddress)) {
        return serverAddress;
    }
    
    // Query for cluster witness service via DNS
    try {
        String clusterName = getClusterName(serverAddress);
        if (clusterName != null) {
            return InetAddress.getByName(clusterName + "-witness");
        }

 *       contents of the current one (for example {@link #transform})
 *   <li>element extraction methods which facilitate the retrieval of certain elements (for example
 *       {@link #last})
 *   <li>query methods which answer questions about the {@code FluentIterable}'s contents (for
 *       example {@link #anyMatch})
 *   <li>conversion methods which copy the {@code FluentIterable}'s contents into a new collection

 *       contents of the current one (for example {@link #transform})
 *   <li>element extraction methods which facilitate the retrieval of certain elements (for example
 *       {@link #last})
 *   <li>query methods which answer questions about the {@code FluentIterable}'s contents (for
 *       example {@link #anyMatch})
 *   <li>conversion methods which copy the {@code FluentIterable}'s contents into a new collection

	public final fun password ()Ljava/lang/String;
	public final fun pathSegments ()Ljava/util/List;
	public final fun pathSize ()I
	public final fun port ()I
	public final fun query ()Ljava/lang/String;
	public final fun queryParameter (Ljava/lang/String;)Ljava/lang/String;
	public final fun queryParameterName (I)Ljava/lang/String;
	public final fun queryParameterNames ()Ljava/util/Set;

* **Sự hỗ trợ từ các trình soạn thảo**.
* **Kiểm tra kiểu dữ liệu (type checking)**.

...và **FastAPI** sử dụng các khia báo để:

* **Định nghĩa các yêu cầu**: từ tham số đường dẫn của request, tham số query, headers, bodies, các phụ thuộc (dependencies),...
* **Chuyển dổi dữ liệu*: từ request sang kiểu dữ liệu được yêu cầu.
* **Kiểm tra tính đúng đắn của dữ liệu**: tới từ mỗi request: