add a failsafe where if you're about to serve a consensus that you know is obsolete, don't do it
is offering me a microdesc consensus document which is
valid-until 2016-09-28 22:00:00. Today is Oct 31.
That relay knows what time it is -- when I establish my Tor channel to it and do a begindir fetch, it gives me good answers in the http header responses.
Yet it is happy to give me a consensus that's a month old. And my Tor client doesn't complain in any obvious useful way. I just get the cryptic line:
Oct 31 23:12:29.455 [notice] I learned some more directory information, but not enough to build a circuit: We have no recent usable consensus.
Is there a consensus age past which the correct answer for a dir cache in that situation should be "I'm really sorry, but it's for your own good: 404"?
We wouldn't want that age to be too small, or the network would fall over a lot faster in the case where it really has been 15 hours since the directory authorities made a consensus.
(Also, is 404 the right return code? It isn't that I don't have it, it's that you're not going to like it.)