Re: #1416 Reinjection - an attempted summary, and a suggested resolution

[Russ Allbery <rra@xxxxxxxxxxxx>]

Charles Lindsey <chl@xxxxxxxxxxxxxxxx> writes:

> But if an injecting agent is aware of the cutoff of its immediately
> following relaying agent (which is a reasonable assumption, because they
> are often two aspects of the same agent), then it will also be aware
> whether said relaying agent understands Injection-Date. In which case
> that SHOULD should not apply. IOW, what you are proposing should be
> regarded as only a temporary measure for use when Injection-Date is not
> observed (i.e.  a continuation of what some agents are currently doing
> anyway).

Yes, exactly.  I think that the root of our disagreement is again that I
believe said transition period until Injection-Date is widely enough
observed that an article with a very stale Date will propagate usefully is
on the order of five to ten years.

>> I don't agree with this at all.  I think that you're selling posting
>> agents short.  Many posting agent authors know very well what identity
>> model they're using and know that Date plus Message-ID make up the
>> message's identity, and provide header fields appropriately.  We will
>> cause problems if we break this.

> If you are saying that some posting agents deliberately don't add the
> Date header until they are actually about to inject, then that is fine,
> and in future they will be doing the same with Injection-Date. But I
> suspect the majority of current agents either create the Date at
> composition time, or else don't create it at all.

I believe that some posting agents deliberately add the Message-ID and
Date header so that they can inject the article with the same identity to
multiple servers simultaneously.  I know that at least some proxies have
that capability.  If each injecting agent then adds their own
Injection-Date, we break the identity model.

>> This will continue to work as expected in my proposal (just to be
>> clear) since in that case the injecting agent can add an Injection-Date
>> as well (and indeed MUST).

> Yes, but what I want is MUST when Injection-Date is absent, irrespective
> of whether Date is present or not. I still do not see what can go wrong
> in that situation. Can you construct an example?

Sure.  Suppose that I'm using a local news proxy which talks to three
different remote servers for me and presents me with a combined view of
newsgroups from those servers.  (This is an increasingly common substitute
for running a full-fledged local news server, and in some ways works much
nicer.)  Suppose that for maximum propagation (for exactly the same sorts
of reasons that you do something similar with C News), I have it
configured to post my messages to all of those remote servers at the same
time.

If one of those servers is down at the time of the posting, the safest and
most reliable behavior, and the one that I believe is currently
implemented in at least some software of this sort, is to queue the post
and keep trying.

So you potentially get multiple injection separated by time, which if
Injection-Date is added separately by each injection agent creates the
possibility of duplicate articles via the means that we've just been
discussing in this thread.

-- 
Russ Allbery (rra@xxxxxxxxxxxx)             <http://www.eyrie.org/~eagle/>