[Qt-interest] QNetworkProxyFactory::setUseSystemConfiguration(true) slows down network access, even though proxy not used

[Tony Rietwyk]

Hi Everybody, 

My application uses QNAM.post to communicate with a server.  I had assumed
that QNAM would automatically use the system proxy settings if they were
required.  I have no idea how to setup an Apache proxy server to test this,
though.  The sales guy asked if we supported clients using proxies.  Looking
at the docs, I get the impression that proxies are NOT supported by default.
So I changed the startup code to add a call to
setUseSystemConfiguration(true) anyway.  Now every network access is much
slower - at least 1 second.  (The code shows a progress popup after a 1
second timeout, and it is constantly popping up, then disappearing).  I do
not have a proxy set on my system. 

I'm using 4.6.0 commercial downloads on Win 7 64-bit,  MS Visual Studio
2008.  

The application has been around for over 15 years (previously as Delphi),
and no-one has ever needed proxy settings - so at this stage, we just want
to be able to tick the proxy box if a new client needs it.  

I do appreciate that we may need to add proxy username/password settings
similar to Skype.  I also understand that there are several different types
of proxies with differing authentication requirements.  All the more reason
to be able to just use the default browser settings.  

Has anybody experienced a similar slow-down?  Is there something else that I
need to do to use the default settings efficiently?  Is there a way to
detect if a proxy will be required during startup and only make the call in
those cases?  

Thanks for any tips or help! 

Tony.