Re: [gnus git] branch master updated: n0-17-27-g43f8466 =1= nntp.el (nntp-open-connection): Set TCP keepalive option.

[Stefan Monnier <monnier@iro.umontreal.ca>]

> Keepalive is usually useful (on the client side) if you have a protocol
> where you're just sitting sleeping on a socket.  If the server dies,
> you'll never get a TCP RST, so the keepalive option will ensure you get
> that RST after a while.

The use case is the one mentioned in the comment: you sit behind a NAT
router.  Gnus connects, sends some commands, gets some responses, then
sits still for some hours because the user goes on to do something else
or reads newsgroup from another server (the machine may be put to sleep
in the mean time, but not necessarily).  When the user comes back to
this newsserver, the IP will often be the same as before, but the NAT
router will have completely forgotten about this open TCP connection, so
Emacs never receives an RST or anything like that and Gnus just sits
there waiting for the answer that'll never come.

> (And, besides, if nntp.el needs keepalive, doesn't all network
> connections need it?)

All the ones that may stay open without activity, yes.
Oddly enough nowadays these are rarely used by the "new" protocols like
http, video-streaming, etc...


        Stefan