⚡🗞️ FastAPI Websocket Pub/Sub

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

Installation 🛠️

pip install fastapi_websocket_pubsub

Intro

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

Usage example (server publishing following HTTP trigger):

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.

Server:

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"])

Client:

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)

More Examples

• 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

What can I do with this?

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

Foundations:

• 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

Logging

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)

Pull requests - welcome!

• Please include tests for new features