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Fiddler solves my HTTPS Post request

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Mauricio asked on 29 Jun 2019, 06:34 PM


Hi All,


I'm trying to solve an issue I've been facing for almost 2 weeks, trying to invoke a web service, using POST over HTTPS, which is getting the message "The underlying connection was closed". The strange thing is that the invoke works well when Fiddler is running on my PC.


I've read several post and forums entries, like the one wrote by Eric:!-running-fiddler-fixes-my-app-. But none of the suggestions there worked for me. The server certificate seems to be trusted by my PC, so I think it's not related to that. 


So is there any way I can see what Fiddler does to change the original request?


The C# code I'm using is as follows, when I'm trying to reach the following web service:


 ServicePointManager.Expect100Continue = true;
 ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;
 ServicePointManager.SetTcpKeepAlive(true, 10000, 10000);
 ServicePointManager.DefaultConnectionLimit = 1000;
 WsSecureSvc.WsSecureClient client = new WsSecureSvc.WsSecureClient();
 WsSecureSvc.resultLog resp = client.log(someParam);


Please let me know if I'm doing something wrong there.

Any help would be really appreciatted as I'm totally stuck on getting this working.


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Eric R | Senior Technical Support Engineer
Telerik team
answered on 08 Jul 2019, 08:00 PM
Hi Mauricio,

Thank you for using the Telerik Fiddler Forums. Just a heads up, I deleted the duplicate posting that contained the same information.

As for as the Underlying Connection Closed issue, without testing the application my first guess would be the Protocol Versioning. More information about which protocol versions Fiddler supports is outlined in the Fiddler and Modern TLS Versions article.

To test this out, try different versions from the application as seen in the Underlying Connection Closed StackOverflow thread.
I hope this helps. Please let me know if you need any additional information.


Eric R
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Eric R | Senior Technical Support Engineer
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