pub async fn process_msg<R: RuntimeIndexer>(
rpc: &LegacyRpcMethods<R::RuntimeConfig>,
trees: &Trees<<R::ChainKey as IndexKey>::ChainTrees>,
msg: RequestMessage<R::ChainKey>,
sub_tx: &UnboundedSender<SubscriptionMessage<R::ChainKey>>,
sub_response_tx: &UnboundedSender<ResponseMessage<R::ChainKey>>,
) -> Result<ResponseMessage<R::ChainKey>, IndexError>