API for Determining if App is Running on Citrix or Terminal Services

Question

I'm looking for an API/function I can call to determine if software is running on Citrix, Terminal Services, or a stand-alone PC. Optimally, it would work something like this:

Select Case APIWhatSystem.Type.ToString
   Case "Citrix"
      bCitrix = True
   Case "TS"
      bTerminalServices = True
   Case "PC"
      bPC = True
End Select

I would prefer something that worked from an API call as opposed to looking at something in the registry as we're having more and more customers that are locking down the registry.

Thanks.

Answer 1

There is an API function that lets you determine whether a specific user session is displayed on the console (locally) or via one the the remoting protocols Citrix ICA (nowadays called HDX) or Microsoft RDP.

Call WTSQuerySessionInformation with 3rd parameter set to WTSClientProtocolType. The function returns:

• 0 for console sessions
• 1 for ICA sessions
• 2 for RDP sessions

Interestingly the return value of 1 is not documented as WTS_PROTOCOL_TYPE_ICA on MSDN (second link above) any more, but as "This value is retained for legacy purposes.".

Update:

XenDesktop sessions cannot be detected with WTSQuerySessionInformation (it returns 0, meaning Console). If you want a universal solution:

• Call WTSQuerySessionInformation. If that returns 1 or 2 (ICA or RDP), you are done.
• If WTSQuerySessionInformation returns 0 (Console), dynamically load wfapi.dll and get the address of WFGetActiveProtocol
• Call WFGetActiveProtocol with a parameter of WF_CURRENT_SESSION, which is defined as ((DWORD)-1)
• The return value of WFGetActiveProtocol is the session type. It should be either 0 (Console) or 1 (ICA)

I have described the process in detail here along with a C++ code sample and a working compiled tool that returns the current session's remoting protocol type.