How to debug a TLSv1.3 protocol problem?

Claus Assmann ca+ssl-users at
Thu May 21 12:28:41 UTC 2020

On Wed, May 20, 2020, Matt Caswell wrote:

> This sounds odd. Why does the client fail because it hasn't read the
> expected data yet? Normally (with non-blocking sockets), a failure to

Sorry, I should have written that the read call is timing out
(doesn't matter whether the timeout is 5s or 20s).

I spent a lot of time debugging the I/O layer which is basically
stdio from Chris Torek/*BSD with timeouts. It seems there is a
problem but I'm not sure whether that's a bug in the code or it is
just not supposed to be used that way (the buffering layer discards
data when it switches from read to write - in case someone is
interested: *wsetup clears the read buffer).

I need some more time to understand the internals of that
code, but it looks like this is not an OpenSSL/TLSv1.3 problem
(it just triggers the problem in the I/O layer).

Thanks for all the help and finally getting me to look at
the "right" place, I appreciate the patience and feedback
(and I learned a lot about the low level debugging and
available callbacks to show data at the various stages).

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