Support header-only feed from innfeed

[eagle]

Implements Diablo-style MODE HEADFEED. It might be better to wait for some standardization of the protocol before adding something like this.

From Miquel van Smoorenburg:

This is a patch I've had laying around for a few years and that I never got around to testing. It's against inn-2.4.1 and compiled fine in 2004, but its completely untested.

Anyway I'm posting it here so that it's in the archives, so that if anyone ever wants to implement this functionality inn innfeed they have a possible starting point.

[eagle]

Patch against INN 2.4.1

[Julien ÉLIE]

Not a compliance with standards, strictly speaking. But it may be in the future. That's why I mark this ticket as related to NNTP compliance.

[Julien ÉLIE]

See this thread in the ​IETF-NNTP mailing-list:

Does the Diablo implementation do streaming for header feeds? If so, we need a header-only equivalent for TAKETHIS, maybe TAKEHEADER.

I think it does streaming but I am not sure. And CHECK also needs to be split in order to know whether the news server only has the headers (?)
And IHAVEHDR?

We'd need more information about how it's used. Does it rely on being able to distinguish between CHECK for a header and CHECK for a full article? What does a Diablo implementation with a header feed do if it gets a traditional CHECK for an article for which it has only the header? It may be that it's not that complicated.

Given that it's a new protocol, it's not clear to me that there's any reason to bother with an IHAVE equivalent. Again, though, we'd have to look at Diablo and see if it implements both.