NFD

In 2014 Face design, FaceManager invokes Face::getFaceStatus method on every face to obtain its FaceStatus struct.

In #3177, Face::getFaceStatus is eliminated, and FaceManager becomes responsible to populate the FaceStatus struct, but "remaining lifetime" field wasn't considered.

Currently, Face class and Transport class lack a getter for FaceManager to obtain or compute "remaining lifetime".

To fix this bug, a getter needs to be defined in "dynamic properties" section.

/** \return expiration time of the face
 *  \retval time::steady_clock::TimePoint::max() the face has indefinite lifetime
 */
time::steady_clock::TimePoint
getExpirationTime() const;

Is this field only applicable to unicast UDP or is it also used by other Transports?

Nevermind the question in note 3.

However, I have another question: FaceManager::collectFaceProperties is used with both FaceStatus and FaceEventNotification, the former having an ExpirationPeriod field, while the latter does not. As such, I see two options to proceed: Either remove the template and create separate functions for each class or add an ExpirationPeriod field to FaceEventNotification. Does anyone have any better ideas?

Answer to note-3:

Face lifetime is applicable to on-demand datagram faces only.

Answer to note-4:

1. Introduce ndn::nfd::FaceStatus FaceManager::collectFaceStatus(const Face& face, time::steady_clock::TimePoint now) static method, that calls FaceManager::collectFaceProperties and Face:: getExpirationTime.
2. Merge collectFaceCounters into collectFaceStatus since this is the only usher.
3. Use collectFaceStatus in both listFaces and queryFaces.