celery-salt 1.5.0

Event-driven architecture library for Python that extends Celery with event publishing/subscribing patterns

CelerySalt

A schema-driven event API on top of Celery: publish/subscribe (broadcast) and RPC with Pydantic validation and a schema registry.

Features

• Pydantic schemas: type-checked event payloads with validation.
• Broadcast: fire-and-forget pub/sub (one event to many subscribers).
• RPC: request/response with response and error schema validation.
• Schema registry: schema registration and lookup by topic/version.
• Versioning: topic stays stable; versions are metadata.
• Django integration: optional helpers for wiring queues and module discovery.
• Protocol compatibility: interoperates with tchu-tchu (tchu_events exchange and _tchu_meta).

Quick Start

Installation

pip install celery-salt

Broadcast Example

from celery_salt import event, subscribe

# Define event schema
@event("user.signup.completed")
class UserSignupCompleted:
    user_id: int
    email: str
    company_id: int
    signup_source: str = "web"

# Publish event
UserSignupCompleted.publish(
    user_id=123,
    email="[e-mail]",
    company_id=1,
    signup_source="web"
)

# Subscribe to event
@subscribe("user.signup.completed")
def send_welcome_email(data: UserSignupCompleted):
    print(f"Sending welcome email to {data.email}")

RPC Example

from celery_salt import event, subscribe, RPCError

# Define RPC request/response schemas
@event("rpc.calculator.add", mode="rpc")
class CalculatorAddRequest:
    a: float
    b: float

@event.response("rpc.calculator.add")
class CalculatorAddResponse:
    result: float
    operation: str = "add"

@event.error("rpc.calculator.add")
class CalculatorAddError:
    error_code: str
    error_message: str

# Handler
@subscribe("rpc.calculator.add")
def handle_add(data: CalculatorAddRequest) -> CalculatorAddResponse:
    return CalculatorAddResponse(result=data.a + data.b, operation="add")

# Client call (returns SaltResponse: .event, .data, .payload, attribute access)
response = CalculatorAddRequest.call(a=10, b=5, timeout=10)
print(f"Result: {response.result}")  # 15.0
# For DRF/JsonResponse: use response.payload (JSON-serializable dict/list)

Architecture

Publisher → RabbitMQ Exchange (tchu_events) → Subscribers

• Exchange: tchu_events (topic exchange, protocol compatible)
• Routing: Topic-based with wildcard support (user.*, #)
• Serialization: JSON with Pydantic validation
• Result Backend: Redis (required for RPC)

Documentation

• Examples: ./examples/
• Docs: ./docs/
• Unified API (SaltEvent / SaltResponse): ./docs/EVENT_CLASS_UNIFIED_API.md
• Typing subscriber payloads: ./docs/TYPING_SUBSCRIBER_EVENTS.md

Requirements

• Python 3.10+
• Celery 5.3+
• RabbitMQ (message broker)
• Redis (optional, required for RPC)

Django is optional. The core library is Celery + Pydantic; events and validation do not require Django. Install with pip install celery-salt[django] only if you use the optional Django helpers below.

Django (optional)

If you use Django:

1. Wire the Celery app
   Add 'celery_salt.django' to INSTALLED_APPS and set CELERY_APP = "myproject.celery:app" in settings. Then .publish() and .call() work from views with no extra code.

2. Configure the worker
   In your celery.py, call setup_celery_queue(app, queue_name="my_queue", subscriber_modules=[...]) so the dispatcher task is bound to your queue and @subscribe handlers.

3. Optional: auto-publish on model save/delete
   Use the @auto_publish decorator on a Django model to publish events on create/update/delete.

Examples

See the examples directory for complete working examples:

• Basic Broadcast - Pub/sub messaging
• Basic RPC - Request/response pattern

Run examples with Docker Compose:

cd examples
docker-compose up -d  # Starts RabbitMQ and Redis

Key Concepts

Event Schemas

Schemas are defined using Pydantic models and registered at import time:

@event("user.created")
class UserCreated:
    user_id: int
    email: str
    created_at: datetime

Publishing Events

# Broadcast (fire-and-forget)
UserCreated.publish(user_id=123, email="[e-mail]", created_at=datetime.now())

# RPC (synchronous)
response = CalculatorAddRequest.call(a=10, b=5, timeout=10)

Subscribing to Events

@subscribe("user.created")
def handle_user_created(data: UserCreated):
    # Process event
    pass

RPC Response Validation

@event.response("rpc.calculator.add")
class CalculatorAddResponse:
    result: float

@event.error("rpc.calculator.add")
class CalculatorAddError:
    error_code: str
    error_message: str

Protocol Compatibility

CelerySalt maintains protocol compatibility with tchu-tchu:

• Same exchange name: tchu_events
• Same message format: _tchu_meta field
• Same routing key conventions

This allows gradual migration: apps using celery-salt can communicate with apps still using tchu-tchu.

Development

git clone https://github.com/sigularusrex/celery-salt.git
cd celery-salt

# tests
python -m pytest

License

MIT License - see LICENSE file for details.

Contributing

Please open an issue or pull request on GitHub.

Links

• GitHub: https://github.com/sigularusrex/celery-salt
• Issues: https://github.com/sigularusrex/celery-salt/issues