Frequent Prefix Registration Failure

[justincpresley]

System: Ubuntu 20.04

Forwarder Version: NFD-nightly, latest pull

Scope: Likely just my machine / Individual Experience via configuration / setup

Error Frequency: Around 1 per 10 registrations

Problem: When working with applications (running it multiple times) that listen to around 6+ different prefixes, I occasionally get this error Registration for PREFIX failed: 403 authorization rejected. Since the frequency does not happen every run, I am able to just restart the application in order to successfully test what I need to test. However, I am curious on what could be the issue and ways to prevent this. What do you suggest or know about this problem? Any configuration that might help?

Notes: Everything else related to the Forwarder works as intended and I can perform all the other related operations.

[yoursunny]

My packages are built from the named-data/ppa-packaging.
You'll see the exact same error if you install from named-data/ppa.
This is not a bug in my build procedure, as I do not modify build scripts other than overwriting version numbers.

Your error message appears to come from python-ndn.
python-ndn is not implementing stop-and-wait correctly:

• Prefix registration commands are sequenced with a semaphore: https://github.com/named-data/python-ndn/blob/8867844971888e0c998d01c2af735faca7b75a3d/src/ndn/app.py#L404
• However, timestamp value is already derived from current clock: https://github.com/named-data/python-ndn/blob/8867844971888e0c998d01c2af735faca7b75a3d/src/ndn/app_support/nfd_mgmt.py#L230
• If NFD responds quickly such that two commands were sent in the same milliseconds, they have the same timestamp value, which violates the protocol.

The library should increment the timestamp on subsequent commands.

[yoursunny]

I do not modify build scripts other than overwriting version numbers.

While not related to this issue, this statement requires a correction:

Nowadays I indeed modify build scripts, not only version numbers, but also dependencies.
For example, libboost-all-dev is replaced with more specific packages, so that it would not bring in Python 2 ☠️.

I avoid modifying the source code though, so that with high probability, my builds have the same runtime behaviors as the PPA builds on the same source code version.