Relay Modern: Connecting websocket to network layer

I’m having issues figuring out how to connect the Relay Modern network layer with my websocket instance.

I’m currently instantiating a websocket instance as:

const subscriptionWebSocket = new ReconnectingWebSocket('ws://url.url/ws/subscriptions/', null, options);

I'm specifying the subscription and creating a new instance of requestSubscription:

const subscription = graphql`
  subscription mainSubscription {
    testData {
      anotherNode {
        data
      }
    }
  }
`;

requestSubscription(
  environment,
  {
    subscription,
    variables: {},
    onComplete: () => {...},
    onError: (error) => {...},
    onNext: (response) => {...},
    updater: (updaterStoreConfig) => {...},
  },
);

Which then allows me to send any subscription requests:

function subscriptionHandler(subscriptionConfig, variables, cacheConfig, observer) {
  subscriptionWebSocket.send(JSON.stringify(subscriptionConfig.text));

  return {
    dispose: () => {
      console.log('subscriptionHandler: Disposing subscription');
    },
  };
}

const network = Network.create(fetchQuery, subscriptionHandler);

through to my server (currently using Graphene-python), and I’m able to interpret the received message on the server.

However, what I’m having issues figuring out is how to respond to a subscription; for example, when something changes in my DB, I want to generate a response and return to any potential subscribers.

The question being, how do I connect the onMessage event from my websocket instance into my Relay Modern Network Layer? I've browsed through the source for relay but can't seem to figure out what callback, or what method should be implementing an onreceive.

Any tips are appreciated.