Ah I think I found it:

On Nov 11, 2014, at 09:59 , Quinn The Eskimo! <eskimo1@apple.com> wrote:

Preflighting is almost always a mistake. The problem is that it's /really/ hard to tell whether a connection will succeed. The only way to know for sure is to try it. Doing a reachability preflight never helps because:

o reachability saying "yes" doesn't mean the connection will succeed (obviously), so you still have to deal with errors anyway

o reachability saying "no" doesn't guarantee that the connection will fail

This last one is a kicker because you're actively preventing folks from trying something that might have actually worked.

Reachability is good for guiding your retry policy and for improving error status in the event of an actual failure, but don't preflight connections.

On Jun 8, 2015, at 15:56 , Rick Mann <rmann@latencyzero.com> wrote:

I thought I'd seen advice from Apple engineers (Quinn?) that instead of first checking SCNetworkReachability, we should just try to make the actual connection, and then take action (e.g. alert the user) only if that fails.

But of course, if there's going to be a long timeout, I don't want to make the user wait that long.

In my app, there are many moving parts. Background processes try to make network connections (that should not necessarily complain if they fail), sometimes the user initiates network connections...it's challenging to get it all correct.

What was the specific advice regarding checking SCNR vs. just trying to connect?

Thanks,

-- Rick Mann rmann@latencyzero.com

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