class_docstr: OpenAPIServiceConnector connects to OpenAPI services, allowing for the invocation of methods specified in
  an OpenAPI specification of that service. It integrates with ChatMessage interface, where messages are used to
  determine the method to be called and the parameters to be passed. The message payload should be a JSON formatted
  string consisting of the method name and the parameters to be passed to the method. The method name and parameters
  are then used to invoke the method on the OpenAPI service. The response from the service is returned as a
  ChatMessage.
  
  Before using this component, one needs to register functions from the OpenAPI specification with LLM.
  This can be done using the OpenAPIServiceToFunctions component.
docstr: Invokes the specified method on the OpenAPI service.
  
  :param openapi_service: The OpenAPI service instance.
  :type openapi_service: OpenAPI
  :param method_invocation_descriptor: The method name and arguments.
  :type method_invocation_descriptor: Dict[str, Any]
  :return: A service JSON response.
  :rtype: Any
  :raises RuntimeError: If the method is not found or invocation fails.
code: def _invoke_method(
      self,
      openapi_service: OpenAPI,
      method_invocation_descriptor: Dict[str, Any],
  ) -> Any:
      """
      Invokes the specified method on the OpenAPI service.
  
      :param openapi_service: The OpenAPI service instance.
      :type openapi_service: OpenAPI
      :param method_invocation_descriptor: The method name and arguments.
      :type method_invocation_descriptor: Dict[str, Any]
      :return: A service JSON response.
      :rtype: Any
      :raises RuntimeError: If the method is not found or invocation fails.
      """
      name = method_invocation_descriptor["name"]
      # a bit convoluted, but we need to pass parameters, data, or both to the method
      # depending on the openapi operation specification, can't use None as a default value
      method_call_params = {}
      if (
          parameters := method_invocation_descriptor["arguments"].get(
              "parameters"
          )
      ) is not None:
          method_call_params["parameters"] = parameters
      if (
          arguments := method_invocation_descriptor["arguments"].get(
              "requestBody"
          )
      ) is not None:
          method_call_params["data"] = arguments
  
      method_to_call = getattr(openapi_service, f"call_{name}", None)
      if not callable(method_to_call):
          raise RuntimeError(
              f"Operation {name} not found in OpenAPI specification {openapi_service.info.title}"
          )
  
      # this will call the underlying service REST API
      return method_to_call(**method_call_params)
  
file_path: haystack/haystack/components/connectors/openapi_service.py
imports: import json
  import logging
  from typing import List, Dict, Any, Optional
  from haystack import component
  from haystack.dataclasses import ChatMessage, ChatRole
  from haystack.lazy_imports import LazyImport
label_desc: Use image node_id 5 for calling the OpenAPIServiceConnector obj's underlying member method code with example usage: obj._invoke_method(openapi_service, method_invocation_descriptor) and returns: method_to_call