Strange Proxy Issue, or Connection Issue

[Andrew.W]

Background: Application works reliably on a number of different sites, both directly and indirectly through a proxy. Our application opens about 3 connections to our server that it uses for different things.

A strange issue has come up on a user site with Windows 7 and a Proxy server. What is happening is that the some of the httpcli connections are working (the 1st one) but others are failing (connects but then you get connection lost). The app absolutely uses the same connections, and it works well in all other cases.

The problem is only seen on Windows 7 machines with a Proxy.

[D.Tkalcec (RTC)]

I'm not sure about Windows 7, but on Windows Vista and older when using the WinInet API (useProxy=TRUE; useWinHTTP=False) you are limited to 2 physical connections per destination address in your application. If your application expects to have 3 working physical connections to the same address and port, only 2 of them will be working while the 3rd one will always end up in a queue waiting for one of the other 2 to become available.

As said, I did not test this under Windows 7, but it is possible that the above behavior was changed by MS in Windows 7 to report a connection problem if you try using a 3rd connection while 2 other connections are already in use.

If the issue is related to this WinInet API limitation and NOT a limitation of some Proxy Server through which the connections are routed, you should be able to solve the problem by switching over to the WinHTTP APIs (set useWinHTTP to TRUE). The WinHTTP does not have such a low limit on the number of physical connections, but it forces you to set up proxy parameters manually (for example, entering the ProxyAddress, ProxyUsername and ProxyPassword in the UserLogin property on the TRtcHttpClient component).

The only other solution I can think of is to redesign your application to work with max 2 physical connections at a time (use only 2 TRtcHttpClient components).

Best Regards,
Danijel Tkalcec

[Andrew.W]

Thanks Daniel, a quick follow up question. Does the option to use SSL work with WinHttp as it does with Wininet?

[D.Tkalcec (RTC)]

Yes, the RTC SDK has the same SSL support when using the WinHTTP API as with the WinInet API.

Best Regards,
Danijel Tkalcec