Negotiation fails with `rmw_cyclonedds_cpp`

[nvcyc]

Negotiated publisher holds a callback to trigger additional negotiation when it detects a change in graph in terms of the list of negotiated subscriber connected to the same topic. The list is based on ROS pub/sub internal GIDs.

A GID is recorded here when a negotiated subscriber is connected:

negotiated/negotiated/src/negotiated_publisher.cpp

Lines 498 to 501 in eac198b

	std::copy(
	std::begin(msg_info.get_rmw_message_info().publisher_gid.data),
	std::end(msg_info.get_rmw_message_info().publisher_gid.data),
	std::begin(gid_key));

It gets a GID in a different way to check if a connected negotiated subscriber (more precisely, its negotiation publisher) is already existed here:

negotiated/negotiated/src/negotiated_publisher.cpp

Lines 389 to 393 in eac198b

	if (negotiated_subscription_type_gids_->count(endpoint.endpoint_gid()) > 0) {
	std::vector<std::string> old_type =
	negotiated_subscription_type_gids_->at(endpoint.endpoint_gid());
	new_negotiated_subscription_gids->emplace(endpoint.endpoint_gid(), old_type);
	}

In rmw_fastrtps_cpp GIDs obtained from these two methods are identical, but they are different when using rmw_cyclonedds_cpp, which causes the algorithm to think that a negotiated has been removed and hence removing all negotiated results. As a result, negotiation can fail in rmw_cyclonedds_cpp when it should be successful.