Broadcasting a message from a manager to clients in websocket using fastapi

[artaasd95]

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Example Code

from typing import List

from fastapi import FastAPI, WebSocket, WebSocketDisconnect
from fastapi.responses import HTMLResponse

app = FastAPI()

class ConnectionManager:
    def __init__(self):
        self.active_connections: List[WebSocket] = []

    async def connect(self, websocket: WebSocket):
        await websocket.accept()
        self.active_connections.append(websocket)

    def disconnect(self, websocket: WebSocket):
        self.active_connections.remove(websocket)

    async def send_personal_message(self, message: str, websocket: WebSocket):
        await websocket.send_text(message)

    async def broadcast(self, message: str):
        for connection in self.active_connections:
            await connection.send_text(message)

manager = ConnectionManager()


@app.get("/")
async def get():
    return (f"Hi!")


@app.websocket("/ws/{client_id}")
async def websocket_endpoint(websocket: WebSocket, client_id: int):
    await manager.connect(websocket)
    try:
        while True:
            data = await websocket.receive_text()
            await manager.send_personal_message(f"You wrote: {data}", websocket)
            await manager.broadcast(f"Client #{client_id} says: {data}")
    except WebSocketDisconnect:
        manager.disconnect(websocket)
        await manager.broadcast(f"Hello everyone")

Description

I want to make a websocket server using Fastapi then get a message from a manager then broadcast it to all clients. The messages are just text. Here is the process:

The manager connects to server.
The clients connect to server.
The manager send a message to server and server receive the message(could send OK status or response for error handling)
The server broadcast the message to all clients(no matter to manager or not)
The manager and clients are preferred to be MQL4/5 Experts. A simple topology of the system:

The server is using fastapi sockets FastAPI websocket

The simple server code like the above code The manager of system

I want to know how can I connect the manager to system the get it's message and broadcast it. I want to know how can I make the system.

Operating System

Windows

Operating System Details

No response

FastAPI Version

0.75.1

Python Version

3.8.12

Additional Context

No response

[jgould22]

I am not super well versed in this space but one way would be to use a message broker.

Use a message broker of some type and when you accept requests on your web socket you can either make that connection a publisher or a subscriber to your message brokers topic.

Redis is one option https://redis.io/docs/manual/pubsub/ but there are many in this space that you could investigate.

Another option might be to use some form of queue between the publishers and the subscribers but you might run into issues depending on how you choose to deploy the service.

[accelleon]

Honestly, the code in the example is basically what you want.
Just define a different endpoint for the manager than the clients. Don't listen for messages on websockets connected through the client path, broadcast messages received on the manager path.

[mauroalejandrojm]

Bear in mind the mdn web docs about websockets to learn a little more about how does a WebSocket work and then, you can follow tiagolo's explanation about WebSockets in FastAPI. Also there is an example I posted for another question.

The main idea of the example is to show that the server is going to create a WebSocket and served at the localhost or cloud machine endpoint.

Each time a client tries to connect to the server a client Id is assigned to that user. so let's say a new client tries to connect to the endpoint a client Id is assigned to that user by the server and the endpoint for that client would look like http://127.0.0.1:8000/1650006000079, another client might try to connect with an endpoint like ws://127.0.0.1:8000/ws/1649927783794, if one of the clients due to the manager left or send a message, that information is broadcasted from the server to all the clients, that is due to the code and logic under the WebSocket decorator, but you can change it to your requirements.

Also notice that I'm using the WebSocket using the include_router method but you can use tiagolo's example that you posted.

[parth-bril22]

@mauroalejandrojm Can you please tell how can we customise the code where each client and manager's chat doesn't show to all other clients which are connected ?

[mauroalejandrojm]

Hello parth,

I hope you are having a really great day.

you can check the documentation about WebSockets, specificly at Handling disconnections and multiple clients websockets, you can see when tiagolo creates the instance manager using the ConnectionManager Class, this class has some methods that use the WebSocket class from fastapi. There is a method called broadcast in the ConnectionManager that allows you to send message to all active connections, so if you don't want to send a message from one client to another don't call that method or comments the calls from that method:

# main.py
@app.websocket("/ws/{client_id}")
async def websocket_endpoint(websocket: WebSocket, client_id: int):
    await manager.connect(websocket)
    try:
        while True:
            data = await websocket.receive_text()
            await manager.send_personal_message(f"You wrote: {data}", websocket)
            # await manager.broadcast(f"Client #{client_id} says: {data}")
    except WebSocketDisconnect:
        manager.disconnect(websocket)
        # await manager.broadcast(f"Client #{client_id} left the chat")

Best regards!

[parth-bril22]

@mauroalejandrojm Thank you so much for solution. It helps me.

Actually , I want to use fastapi web-socket for the chat application where admin can interact with each client privately.

[mauroalejandrojm]

what do you mean when you are referring to interact, the admin is a bot that automatically responds to clients based on some condition or regular expression match or the admin is an actual person reading and sending responses manually to each client?

[parth-bril22]

the admin is actual person reading and sending responses manually to each client

[mauroalejandrojm]

the admin is actual person reading and sending responses manually to each client

I think you can break the problem into a small sets of subproblems which in conjunction can solve the problem, take a look at the methods implemented by tiagolo and add the parts that you require, it doesn't have to be complex using database or admin portal, just try to simplify the process:

*Catching messages from clients can be model using arrays, or tuples using the client id.
*creating an endpoint for the admin to send message to clients.

Once you are done with those task, you can increase the complexity adding databases, changing data type to match your needs and so on.

[tiangolo]

Thanks for the help here everyone! 👏 🙇

If that solves the original problem, then you can close this issue @artadp ✔️

[github-actions]

Assuming the original need was handled, this will be automatically closed now. But feel free to add more comments or create new issues or PRs.