Could anyone provide a fastapi websocket endpoint which could connect with the example given for RTK Query streaming updates

I'm trying to get my head around RTK Query as it applies to websockets. The example given is

import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react'
import { createEntityAdapter, EntityState } from '@reduxjs/toolkit'
import { isMessage } from './schemaValidators'

export type Channel = 'redux' | 'general'

export interface Message {
  id: number
  channel: Channel
  userName: string
  text: string
}

const messagesAdapter = createEntityAdapter<Message>()
export const api = createApi({
  baseQuery: fetchBaseQuery({ baseUrl: '/' }),
  endpoints: (build) => ({
    getMessages: build.query<EntityState<Message>, Channel>({
      query: (channel) => `messages/${channel}`,
      transformResponse(response: Message[]) {
        return messagesAdapter.addMany(
          messagesAdapter.getInitialState(),
          response
        )
      },
      async onCacheEntryAdded(
        arg,
        { updateCachedData, cacheDataLoaded, cacheEntryRemoved }
      ) {
        const ws = new WebSocket('ws://localhost:8080')
        try {
          await cacheDataLoaded

          const listener = (event: MessageEvent) => {
            const data = JSON.parse(event.data)
            if (!isMessage(data) || data.channel !== arg) return

            updateCachedData((draft) => {
              messagesAdapter.upsertOne(draft, data)
            })
          }

          ws.addEventListener('message', listener)
        } catch {}
        await cacheEntryRemoved
        ws.close()
      },
    }),
  }),
})

export const { useGetMessagesQuery } = api

for the frontend. It looks as though the idea is to make a request to /messages/{channel} and on successful receipt and caching of these messages to connect to a websocket api. I'm struggling to create a fastapi app that connects with this example so I can figure out the workings. Does anyone have an example they might be willing to please share?