public boolean unsubscribe(final UnsubscribeRequest request) {
    final Long subscriptionId = request.getSubscriptionId();
    final String connectionId = request.getConnectionId();

    LOG.debug("Unsubscribe request subscriptionId = {}", subscriptionId);

    final Subscription subscription = subscriptions.get(subscriptionId);
    if (subscription == null || !subscription.getConnectionId().equals(connectionId)) {
      throw new SubscriptionNotFoundException(subscriptionId);
    }

    destroySubscription(subscriptionId);

    return true;
  }
The SubscriptionManager is responsible for managing subscriptions and sending messages to the
clients that have an active subscription.
ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/jsonrpc/websocket/subscription/SubscriptionManager.java