Override @c Publisher Default Endpoint

 namespace pubsub = ::google::cloud::pubsub; using ::google::cloud::Options; [](std::string project_id, std::string topic_id) { auto topic = pubsub::Topic(std::move(project_id), std::move(topic_id)); return pubsub::Publisher(pubsub::MakePublisherConnection( std::move(topic), Options{}.set<google::cloud::EndpointOption>( "private.googleapis.com"))); }