TIdHTTP.Get timeouts while the same call done with Postman succeeds: possible reasons?-CodePudding

I call a webapi with a Delphi app, in some pcs, the call timeouts, while in other it works fine.

The request done with Postman works fine.

It is a simple custom ping webservice (URL is in Edit1.Text in the code below), in fact the answer is a textual "Pong".

This is the Delphi code of the call:

 errormsg := '';
  {
  old way of setting custom headers
   IdHTTP1.Request.CustomHeaders.AddValue('X-HTTP-Method-Override', 'ForwardCommand');
  IdHTTP1.Request.CustomHeaders.AddValue('Connection', 'keep-alive');
  IdHTTP1.Request.CustomHeaders.AddValue('Accept', '*/*');
  IdHTTP1.Request.CustomHeaders.AddValue('User-Agent', 'QualibusSilent');
  IdHTTP1.Request.CustomHeaders.AddValue('Content-Type', 'text/plain');
   }
   //better way of setting custom headers
  IdHTTP1.Request.MethodOverride := 'ForwardCommand';
  IdHTTP1.Request.Connection := 'keep-alive';
  IdHTTP1.Request.UserAgent   := 'myCustomUserAgent';
  IdHTTP1.Request.ContentType   := 'text/plain';
  IdHTTP1.Request.Accept   := '*/*';
      IdSSLIOHandlerSocketOpenSSL1 :=  TIdSSLIOHandlerSocketOpenSSL.Create(IdHTTP1);
      IdSSLIOHandlerSocketOpenSSL1.SSLOptions.Mode       := sslmClient;
      IdSSLIOHandlerSocketOpenSSL1.SSLOptions.SSLVersions:= 
        [sslvTLSv1,sslvTLSv1_1,sslvTLSv1_2];
    
  startTime := GetTickCount;
  Try
  sHTML := IdHTTP1.Get(Edit1.Text);
  Except
    On E:Exception do
      errormsg := e.Message;
  End;
  EndTime := GetTickCount;
  ShowMessage('Time taken: '  
    IntToStr(endTime-startTime) #13#10 'Error:' errormsg);

Basically it is a call where instead of GET I do a custom method (ForwardCommand) that I call with X-HTTP-Method-Override.

In the code above I tried to add many headers so that the call is really as the Postman one.

If the call is done directly to the IP address it works, but if I call the https URL it timeouts, there is no evidence of error in the proxy server.

Checking the logs at the webserver side it seems the call is not performed at all.

And this occurs only from some Windows 10 machines, while in the majority of them the call is performed correctly.

Could you please suggest which could be the cause of the error? What should I try to change in the Delphi code to avoid the timeout so that Delphi behaves like Postman?

Thanks.

CodePudding user response：

As stated in comments:

Why when Tidhttp uses proxyParams timeout does not occur and the call succeeds?
...
I finally got the reason for the Postman vs Indy behavior: Proxy. By passing proxy IP and port to TIdHTTP it works, Postman manages to retrieve the system proxy automatically and therefore it works.

There is no "system proxy" on Windows, however there is a proxy in the WinInet API, which is what Internet Explorer (and Edge?) relies on.

In any case, it sounds like the failing PCs don't have direct access to the Internet to begin with, only through a proxy. Indy has no concept of any "system proxy" on any platform, so you will have to assign the proxy settings to TIdHTTP manually, as you have discovered.