25. Backend Development

25.1. XMLRPC Callbacks

The sysXMLRPCRequest.js file in the x0-framework implements the core functionality for handling XML-RPC (Remote Procedure Call) requests, supporting both synchronous and asynchronous operations. Below is an overview of its concept:

25.1.1. Key Concepts

  • Purpose:

    1. Handles communication between the client-side application and backend services using XML-RPC.

    2. Supports ASYNC (asynchronous) request handling.

  • Core Features:
    1. Request Types:

      Supports POST and GET HTTP methods.

    2. Asynchronous Support:

      Implements XMLHttpRequest for making asynchronous requests to the server.

    3. Authentication:

      Includes support for HTTP Basic Authentication with configurable credentials.

    4. Dynamic URL Parameters:

      Allows appending random URL parameters to avoid caching issues during requests.

  • Primary Methods:
    1. setRequestType:

      Configures the HTTP method (e.g., POST or GET).

    2. setRequestBasicAuth:

      Sets up Basic Authentication credentials for the request.

    3. Request:

      Executes the XML-RPC call, processes the response, and invokes the callback function if provided.

  • Callback Handling:

    1. In asynchronous mode, the onreadystatechange method processes the server response and parses it as JSON.

    2. The result is merged or directly assigned to the target object, and the callback function (e.g., callbackXMLRPCAsync) is invoked to handle post-request operations.

  • Session Management:

    1. Includes session data in requests when available, ensuring secure and contextual communication with the backend.

  • Error Handling:

    1. Logs errors and exceptions encountered during request preparation or response processing.

  • Flexibility:

    1. The system allows dynamic configuration of request headers, including Content-Type and Accept.

  • x0-object Callback:

    1. Always execute the x0-systems callbackXMLRPCAsync callback method in the caller x0-object.

25.1.2. Example Workflow

  • A request is initialized using the sysCallXMLRPC constructor with a target URL and optional parameters.

  • Configuration methods (e.g., setRequestType or setRequestBasicAuth) are used to customize the request.

  • The Request method is called with a target object containing data and callbackXMLRPCAsync callback method.

  • In asynchronous mode, the server response is processed, parsed, and passed to the callback function for further action.

25.1.3. Getting Backend Data

x0-application-developer and x0-systems-developer roles should always use x0-service-connector and x0-source-data-objects in the following situations:

  • Developing x0-applications

  • Modeling x0-system-objects

Direct usage of sysXMLRPCRequest is discouraged and should only be done when developing the x0-core-system. See 25.1.5. Nested RPC Requests for more details on nested x0-system XML-RPC calls.

25.1.4. Error Handling

A backend service must return the following JSON syntax when an error has occured:

"Result": {
    "Error": True
    "Exception": "Exception String / Description"
}

If x0-service handling is configured correctly, the AsynNotifyIndicator 14.5. Notify Indicator uses the error-metadata to display error information.

If no error has occured, the Error and Exception properties have to be ommited.

"Result": {
}

25.1.5. Nested RPC Requests

Only relevant for x0-core-system development.

Sometimes multiple / nested (pseudo-synchronous) XML-RPC requests are necessary.

25.1.6. Debugging Information

If something misbehaves drastically, first check Browser JS Console log / debug messages for relevant debugging keywords.

If this wont help, try to comment exception handling in the following files:

  • sysXMLRPCRequest.js

  • sysReactor.js

  • sysFactory.js

  • sysScreen.js

25.2. JSON Schemas

JSON schemas define the structure and validation rules for x0-system-objects. Properly defining JSON schemas ensures consistency and reduces runtime errors.

25.2.1. How to Define JSON Schemas

  1. Schema Structure: Define the schema for each x0-system-object, including required fields, data types, and default values.

  2. Validation: Use JSON schema validation tools to enforce correctness during development and runtime.

  3. Examples: Provide example JSON schemas in the documentation to guide developers.

25.2.2. Best Practices

  1. Version Control: Maintain versioned schemas to handle backward compatibility.

  2. Consistency: Ensure all schemas follow the same conventions and naming patterns.

  3. Documentation: Document the purpose and structure of each schema for easy reference.