Pipeline Behaviors

Pipeline behaviors in Bazario enable pre- and post-processing logic for requests and notifications. These behaviors form a chain around the core handler logic and can modify or enhance the data flow.

Defining Pipeline Behaviors

from bazario import (
    PipelineBehavior,
    Resolver,
    HandleNext,
    Request,
    Notification,
)

# Behavior for all requests
from bazario import PipelineBehavior, HandleNext, Request

class AuthenticationCheckBehavior(PipelineBehavior[Request, Any]):
    def __init__(self, user_provider: UserProvider) -> None:
        self._user_provider = user_provider

    def handle(self, request: Request, handle_next: HandleNext[Request, Any]) -> Any:
        # Check if user is authenticated
        if not self._user_provider.is_authenticated():
            raise PermissionError("User is not authenticated.")

        # Proceed to the next handler or behavior
        return handle_next(request)


# Behavior for all notifications
class AddToEventStoreBehavior(PipelineBehavior[Notification, None]):
    def __init__(self, event_store: EventStore) -> None:
        self._event_store = event_store

    def handle(
        self, 
        request: Notification, 
        handle_next: HandleNext[Notification, None],
    ) -> None:
        self._event_store.add(request)
        return handle_next(request)

# Behavior specific to AddPost request
class AddPostValidationBehavior(PipelineBehavior[AddPost, int]):
    def handle(
        self,
        request: AddPost,
        handle_next: HandleNext[AddPost, int],
    ) -> int:
        if not request.title:
            raise ValidationError("Title required")

        if not request.content:
            raise ValidationError("Content required")

        return handle_next(request)

# Behavior specific to PostAdded notification
class PostAddedEmailBehavior(PipelineBehavior[PostAdded, None]):
    def __init__(self, email_service: EmailService) -> None:
        self._email_service = email_service

    def handle(self, request: PostAdded, handle_next: HandleNext[PostAdded, None]) -> None:
        # Send a thank-you email to the user
        self._email_service.send_email(
            to_user_id=request.user_id,
            subject="Thank you for adding a post!",
            body=f"Dear User {request.user_id}, thank you for your post with ID {request.post_id}!"
        )

        # Proceed with the next behavior or handler
        return handle_next(request)

Registering Pipeline Behaviors

Register your behaviors to Registry. The order of behavior registration determines the execution sequence - behaviors are executed in the order they are added:

from bazario import Registry

def provide_registry() -> Registry:
    registry = Registry()
    # Behaviors will execute in this order:
    # 1. AuthenticationCheckBehavior
    # 2. AddToEventStoreBehavior
    # 3. AddPostValidationBehavior
    # 4. PostAddedEmailBehavior
    registry.add_pipeline_behaviors(Request, AuthenticationCheckBehavior)
    registry.add_pipeline_behaviors(Notification, AddToEventStoreBehavior)
    registry.add_pipeline_behaviors(AddPost, AddPostValidationBehavior)
    registry.add_pipeline_behaviors(PostAdded, PostAddedEmailBehavior)

    return registry

The execution order follows these rules: 1. Global behaviors (registered for base types like Request or Notification) execute first 2. Specific behaviors (registered for concrete types like AddPost or PostAdded) execute after global ones 3. Within each category (global/specific), behaviors execute in the order they were registered 4. For a single request/notification, all applicable behaviors form a chain in this order

Example of execution flow for an AddPost request:

def provide_registry() -> Registry:
    registry = Registry()

    registry.add_behaviors(Request, RequestLoggingBehavior)
    registry.add_behaviors(AddPost, ValidationBehavior, MetricsBehavior)

    return registry

# Execution sequence for AddPost request:
# 1. RequestLoggingBehavior
# 2. ValidationBehavior
# 3. MetricsBehavior
# 4. Actual AddPost handler

Add to your IoC Container:

# ...
container.register(Registry, provide_registry)
# ...

Benefits of Pipeline Behaviors

Pipeline behaviors solve several common issues: - Centralize cross-cutting concerns - Keep handlers focused on business logic - Enable flexible behavior execution order - Eliminate code duplication in validation and response modification