NFD » ndn-tools

I doubt whether or not it is a bug?

The point of using iterative version discovery is to discover the latest version from the producer. (see: https://github.com/named-data/ndn-tools/tree/master/tools/chunks#version-discovery-methods-in-ndncatchunks). It's implemented with the following logic(https://github.com/named-data/ndn-tools/blob/master/tools/chunks/catchunks/discover-version-iterative.cpp):

1. consumer express an Interest, and it hits the content store (assuming producer has died).
2. consumer express the same Interest again (excluding the first one), this Interest gets no route to go since the producer has died.

I think seeing NACK in this case is what it is supposed to be. If a user just wants to retrieve the content without worrying about the latest version, he can use fixed version discovery instead. I've tested the above 5 steps with fixed version discovery, and it works fine.

This is a bug. A network Nack should never result in a worse outcome than a timeout.

Copying Beichuan's argument.

A consumer never knows whether its request will hits the producer or not. Thus the so-called “latest” version is the latest version that is available from the network, not necessarily from the producer. When the producer is not available, the discovery should return the latest version it can find, in this case, the version in the CS. While NACK-NoRoute is fine, the consumer should treat this NACK the same way as it treats a timeout, and concludes that the last version it got is the latest version it can find.

Code review url: https://gerrit.named-data.net/#/c/3778/