Patterns - websockets 12.0 documentation
Description: Here are typical patterns for processing messages in a WebSocket server or client. You will certainly implement some of them in your application. This page gives examples of connection handlers for...

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# Patterns

Here are typical patterns for processing messages in a WebSocket server or client. You will certainly implement some of them in your application.

This page gives examples of connection handlers for a server. However, they’re also applicable to a client, simply by assuming that `websocket` is a connection created with `connect()`.

WebSocket connections are long-lived. You will usually write a loop to process several messages during the lifetime of a connection.

## Consumer

To receive messages from the WebSocket connection:

    async def consumer_handler(websocket):
        async for message in websocket:
            await consumer(message)

In this example, `consumer()` is a coroutine implementing your business logic for processing a message received on the WebSocket connection. Each message may be `str` or `bytes`.

Iteration terminates when the client disconnects.

## Producer

To send messages to the WebSocket connection:

    async def producer_handler(websocket):
        while True:
            message = await producer()
            await websocket.send(message)

In this example, `producer()` is a coroutine implementing your business logic for generating the next message to send on the WebSocket connection. Each message must be `str` or `bytes`.

Iteration terminates when the client disconnects because `send()` raises a `ConnectionClosed` exception, which breaks out of the `while True` loop.

## Consumer and producer

You can receive and send messages on the same WebSocket connection by combining the consumer and producer patterns. This requires running two tasks in parallel:

    async def handler(websocket):
        await asyncio.gather(
            consumer_handler(websocket),
            producer_handler(websocket),
        )

If a task terminates, `gather()` doesn’t cancel the other task. This can result in a situation where the producer keeps running after the consumer finished, which may leak resources.

Here’s a way to exit and close the WebSocket connection as soon as a task terminates, after canceling the other task:

    async def handler(websocket):
        consumer_task = asyncio.create_task(consumer_handler(websocket))
        producer_task = asyncio.create_task(producer_handler(websocket))
        done, pending = await asyncio.wait(
            [consumer_task, producer_task],
            return_when=asyncio.FIRST_COMPLETED,
        )
        for task in pending:
            task.cancel()

## Registration

To keep track of currently connected clients, you can register them when they connect and unregister them when they disconnect:

    connected = set()

    async def handler(websocket):
        # Register.
        connected.add(websocket)
        try:
            # Broadcast a message to all connected clients.
            websockets.broadcast(connected, "Hello!")
            await asyncio.sleep(10)
        finally:
            # Unregister.
            connected.remove(websocket)

This example maintains the set of connected clients in memory. This works as long as you run a single process. It doesn’t scale to multiple processes.

## Publish–subscribe

If you plan to run multiple processes and you want to communicate updates between processes, then you must deploy a messaging system. You may find publish-subscribe functionality useful.

A complete implementation of this idea with Redis is described in the Django integration guide.