Websockets server with anvil

Anvil Q&A
1

Hi all,

Is it possible to setup a websockets server with anvil?

Code below works great when running it on my local computer, but it seems that this code cannot be run in a server-side script in anvil? is that correct?

import asyncio
import websockets

async def handle_websocket(websocket, path):
    # This function will be called whenever a new WebSocket connection is established
    print(f"Client connected to {path}")

    try:
        while True:
            # Wait for data from the client
            message = await websocket.recv()
            print(f"Received message: {message}")

            # Send a response back to the client
            response = f"Received: {message}"
            await websocket.send(response)

    except websockets.exceptions.ConnectionClosed:
        # Handle the case where the connection is closed
        print(f"Client disconnected from {path}")

# Set up the WebSocket server
start_server = websockets.serve(handle_websocket, "localhost", 8765)

# Start the event loop to run the server
asyncio.get_event_loop().run_until_complete(start_server)
asyncio.get_event_loop().run_forever()

I know that i normally can run a uplink (client) but it is not possible in this case since the websockets client code is/will be run from a C# application.

Any help is appreciated!

2

In order for your function to work, it should start and keep running forever.

The Anvil server will kill any function that runs longer than 30 seconds, unless it’s in a background task. And even if it’s in a background task, it could be killed at will.

You may be able to use sockets for short lived tasks, but it’s unlikely to work with long running ones.

3

With anvil-app-server:

runtime_options: {‘server_persist’ : True}

enables persistent server modules. I wonder if your code would run as needed with that configuration.

4

Even with persistent server, processes can be killed. It’s unlikely, most of the time the same process keeps responding, but it is not guaranteed.

5

Thanks, I will try that! So I can pick any port of choice for the websockets server?

6

I would probably run a separate websockets server and use the uplink from there to access anvil data or server-side functions.

1 Like
7

Thanks! Yeah I am considering that :slight_smile: