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Calling remote COM component from MFC client?

I have a COM component that was originally written in Visual Studio 6. It is in a windows service which I have running on one of my development machines. I have written a quick MFC test app to call it and this works fine when run from this machine, the code looks like

COSERVERINFO si; 
MULTI_QI qi; 
COAUTHINFO cai = { RPC_C_AUTHN_NONE, RPC_C_AUTHZ_NONE, 0,RPC_C_AUTHN_LEVEL_NONE, RPC_C_IMP_LEVEL_IMPERSONATE,0, EOAC_NONE };
si.dwReserved1 = 0; 
si.pwszName =L"{machine name}"; 
si.pAuthInfo = &cai; 
si.dwReserved2 = 0; 

qi.pIID = &IID_IMyComponent; 
qi.pItf = NULL;
qi.hr = 1; 

HRESULT hr = CoCreateInstanceEx(CLSID_MyComponent,NULL,CLSCTX_REMOTE_SERVER ,&si,1,&qi);

However, when I move the MFC test app to my other development machine and try and call the component on the other machine it fails. The hresult returned from CoCreateInstanceEx is -2147024891

I have already created the proxy stub DLL and registered it on both machines. Am I missing something else?

UPDATE: I now updated the COUTHINFO structure to the below and it works.

    COAUTHINFO cai = { RPC_C_AUTHN_WINNT, RPC_C_AUTHZ_NONE, 0, RPC_C_AUTHN_LEVEL_DEFAULT, RPC_C_IMP_LEVEL_IMPERSONATE,0, EOAC_NONE };
Solution

  • The ERROR_ACCESS_DENIED is most likely due to the wrong parameters supplied with COAUTHINFO. You set Authentication, Authorization levels to NONE, which is not enough to get permissions to connect with remote machine. Try to set these values: RPC_C_AUTHN_DEFAULT (have COM negotiate the best authentication service), RPC_C_AUTHZ_NONE, RPC_C_AUTHN_LEVEL_DEFAULT, RPC_C_IMP_LEVEL_IMPERSONATE. Also see the MSDN source - COAUTHINFO structure