Signal System

Lback Framework incorporates a Signal system based on a central SignalDispatcher.

This system provides a mechanism for decoupling components by allowing them to notify other parts of the application about events without needing direct references to the listeners.

This is useful for:

  1. Extensibility: Allowing developers to hook into core framework events or application-specific events to add custom logic (e.g., sending emails on user registration, logging specific actions).

  2. Monitoring: Listening to signals related to request lifecycle, errors, cache operations, etc., for logging, monitoring, and debugging purposes.

  3. Decoupling: Keeping components independent of each other, as they only need to know how to send or receive signals, not directly call other components’ methods.

How to Use:

Access the Dispatcher: The framework provides a single, globally accessible SignalDispatcher instance.

This instance is created early in the application’s startup process and can be accessed by importing it from lback.core.dispatcher_instance.

# Example: Connecting a function to a signal
from lback.core.dispatcher_instance import dispatcher # Access the dispatcher

def my_custom_error_handler(sender, **kwargs):
    status = kwargs.get('status_code', 'N/A')
    path = getattr(kwargs.get('request'), 'path', 'N/A')
    print(f"Signal received from: {type(sender).__name__}, Status: {status}, Path: {path}")
dispatcher.connect("error_response_generated", my_custom_error_handler)

  • Signals Emitted by the Framework: The framework emits signals at various points, including:

  • Server Lifecycle: server_starting, server_started, server_shutting_down, server_request_received, server_request_finished, server_response_sent.

  • Middleware Processing: Signals related to the middleware chain and individual middleware execution.

  • Authentication/Authorization: user_login_successful, user_login_failed, admin_login_successful, admin_login_failed, etc.

  • Database/ORM: Signals related to database session management (via SQLAlchemy Middleware).

  • Cache Operations: cache_item_set, cache_hit, cache_miss, cache_item_deleted.

  • Error Handling: error_response_generated, unhandled_exception_response_generated.

  • Initialization: Signals indicating when core components are initialized.

… and many more throughout the framework components.

By connecting your custom logic to these signals, you can extend the framework’s behavior without modifying its core code.

Refer to the documentation or component source code for a full list of available signals and the data they pass.