[stunnel-users] Fullduplex in stunnel

Michal Trojnara Michal.Trojnara at mirt.net
Sat Sep 7 23:42:04 CEST 2013

On 2013-09-05 17:50, Krzysztof Kwiatkowski wrote:
> I'm planning to use stunnel to do stress testing of my application. I
> decided to use stunnel because I've noticed that full-duplex has been
> added to version 3.2 (around 1999) and my application handles high
> throughput.
> AFAIK Stunnel uses openssl. Also I know that openssl doesn't handle
> fullduplex traffic very well. In fact without any tricks, half-duplex
> is most what I could get from openssl.
> As the full-duplex feature has been added to stunnel in 1999 (so long
> time ago) can you confirm that it is still there and full-duplex is
> still supported? If it is a case, how it is possible that stunnel
> handles fullduplex?

Well... It depends on how you define "tricks".  Doing full duplex data
transfer was definitely nontrivial.  Handling of half-closed connections
was was even harder.  My solution boils down to a state machine
implemented with asynchronous handling of read/write/close events using
non-blocking sockets.  All the details you need are within the
transfer() function in the src/client.c file.


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