A fast and durable Pub/Sub channel over Websockets. The easiest way to create a live publish / subscribe multi-cast over the web.

Supports and tested on Python >= 3.7

As seen at PyCon IL 2021 and EuroPython 2021

pip install fastapi_websocket_pubsub 

The classic pub/sub pattern made easily accessible and scalable over the web and across your cloud in realtime; while enjoying the benefits of FastAPI (e.g. dependency injection).

FastAPI + WebSockets + PubSub == ⚡💪 ❤️

• Subscribe

  • Clients subscribe to topics (arbitrary strings) and receive relevant events along with structured data (serialized with Pydantic).

    # Callback to be called upon event being published on server async def on_event(data): print("We got an event! with data- ", data) # Subscribe for the event  client.subscribe("my event", on_event)

• Publish

  • Directly from server code to connected clients.

    app = FastAPI() endpoint = PubSubEndpoint() endpoint.register_route(app, path="/pubsub") endpoint.publish(["my_event_topic"], data=["my", "data", 1])

  • From client to client (through the servers)

    async with PubSubClient(server_uri="ws://localhost/pubsub") as client: endpoint.publish(["my_event_topic"], data=["my", "data", 1])

  • Across server instances (using broadcaster and a backend medium (e.g. Redis, Kafka, ...))
    • No matter which server a client connects to - it will get the messages it subscribes to

    app = FastAPI() endpoint = PubSubEndpoint(broadcaster="postgres://localhost:5432/") @app.websocket("/pubsub") async def websocket_rpc_endpoint(websocket: WebSocket): await endpoint.main_loop(websocket)

    see examples/pubsub_broadcaster_server_example.py for full usage example Note: Requires install with dependencies e.g. pip install fastapi_websocket_pubsub[redis], pip install fastapi_websocket_pubsub[postgres], pip install fastapi_websocket_pubsub[kafka] or pip install fastapi_websocket_pubsub[all] to get support for all three backends

In the code below, a client connects to the server and subscribes to a topic named "triggered". Aside from PubSub websocket, the server also exposes a regular http route, which triggers publication of the event.

import asyncio import uvicorn from fastapi import FastAPI from fastapi.routing import APIRouter from fastapi_websocket_pubsub import PubSubEndpoint app = FastAPI() # Init endpoint endpoint = PubSubEndpoint() # register the endpoint on the app endpoint.register_route(app, "/pubsub") # Register a regular HTTP route @app.get("/trigger") async def trigger_events(): # Upon request trigger an event endpoint.publish(["triggered"])

from fastapi_websocket_pubsub import PubSubClient # Callback to be called upon event being published on server async def on_trigger(data): print("Trigger URL was accessed") async with PubSubClient(server_uri="ws://localhost/pubsub") as client: # Subscribe for the event  client.subscribe("triggered", on_trigger)

• See the examples and tests folders for more server and client examples.
• See fastapi-websocket-rpc depends example to see how to combine with FASTAPI dependency injections

The combination of Websockets, and bi-directional Pub/Sub is ideal to create realtime data propagation solution at scale over the web.

• Update mechanism
• Remote control mechanism
• Data processing
• Distributed computing
• Realtime communications over the web

• Based on fastapi-websocket-rpc for a robust realtime bidirectional channel

• Based on broadcaster for syncing server instances

• Server Endpoint:

  • Based on FastAPI: enjoy all the benefits of a full ASGI platform, including Async-io and dependency injections (for example to authenticate connections)

  • Based on Pydantic: easily serialize structured data as part of RPC requests and responses. Simply Pass Pydantic data models as PubSub published data to have it available as part of an event.

• Client :

  • Based on Tenacity: allowing configurable retries to keep to connection alive

    • see WebSocketRpcClient.init's retry_config

  • Based on python websockets - a more comprehensive client than the one offered by FastAPI

fastapi-websocket-pubsub uses fastapi-websocket-rpc for logging config. It provides a helper logging module to control how it produces logs for you. See fastapi_websocket_rpc/logger.py. Use logging_config.set_mode or the 'WS_RPC_LOGGING' environment variable to choose the logging method you prefer. Or override completely via default logging config (e.g. 'logging.config.dictConfig'), all logger name start with: 'fastapi.ws_rpc.pubsub'

example:

# set RPC to log like UVICORN from fastapi_websocket_rpc.logger import logging_config, LoggingModes logging_config.set_mode(LoggingModes.UVICORN)

• Please include tests for new features