On Sat, 9 Jan 2021, Midnight Wonderer via curl-library wrote:
Regarding CURLOPT_CONNECTTIMEOUT_MS option, I found out that the timeout set
is shared between multiple hosts. Not only that, the allotment is weird,
IMO.
One person's sensible is another person's weird... This is the middle-way:
both sensible and weird.
If you set the connection timeout to 3 seconds, the first server gets 1.5s
budget; the second one gets 750ms, the third 375ms, and so on.
Don't get me wrong; I think splitting into [timeout]/N is equally weird too.
What I actually expect from the connection timeout is: it should be applied
per connection.
There's just no way to satisfy every possible request and desire without
overloading libcurl with even more options.
- Users expect the timeout to expire after the given time, so if the host has
N addresses, they still don't want the timeout to be multiplied with N.
- Users expect that just because one out of the N IP addresses is dead, the
timeout shouldn't needlessly expire and leave the user thinking all addresses
are inaccessible.
These two expectations don't work in combination with: "curl should spend the
entire connection timeout-out time trying to connect to the first IP address".
We simply felt a need to compromise a little.
(Once I attended a meeting with lots of HTTP people, where it was suggested
that maybe clients would be better off happy-eyevalling *every* IP address
that is returned - connect to all of them at once and stick only to the one
that connects the fastest... which would also solve this timeout issue!)
For instance, if I set the timeout to 1s, I expect connection timeouts of 1s
for each try. This is also the behavior of Nginx when used as a reverse
proxy.
So what does nginx do when the first IP address just silently drops all TCP
packets? Fail the connection after one second even if there are also 9 working
IP addresses?
--
/ daniel.haxx.se
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