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pubsub

⚡🗞️ FastAPI Websocket Pub/Sub

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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):
          async with endpoint.broadcaster:
              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_event)

More Examples

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
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