Hello,

I use libcurl in a performance-sensitive application, where timeout
values need to be well-adjusted. An issue has arisen with some domain
names pointing to a round-robin of IP addresses. libcurl tries each IP
address sequentially and divides the timeout value between all of them.
Let's say that I set a connection timeout of 2 seconds, which seems
plenty reasonable for normally responsive hosts. Let's say that I hit
a host pointing to 10 IP addresses. 2s / 10 = 200 ms, so despite my
reasonable 2 seconds timeout, libcurl will try to connect to every IP
with a timeout of only 200 ms. If the host is on another continent, even
with good network connections, this isn't enough, and the 10 connections
will just all fail, timing out one after the other. This is an issue.

Now this behavior may not seem so smart. Personally, if I was trying to
connect by hand, I'd try to first IP address, then if it fails the
second one, then maybe the third one because I'm patient, but no way I'd
go through all 10 addresses just to see them all fail. So I suggest
improving this.

One possibility would be to truncate the list of IP addresses to try,
or to give up after it consistently fails so many times (which is
effectively the same). An interesting idea would be, instead of equally
dividing 2 seconds, to for example try the first address for 1 second,
then if it fails the second one for 500 ms, then the third one for 250
ms and then whatever (if waiting didn't help for the first address, I'm
not very likely to wait a long time for the following ones too). Another
way would be to guarantee a minimum value above the RTT (like 500 ms)
below which the connect timeout for one address won't drop when divided
between many of them; this value could be either hardcoded or a new
configuration option. What do you think?

Regards,

-- 
Pierre Ynard
"Une âme dans un corps, c'est comme un dessin sur une feuille de papier."
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