Programmatically registering and unregistering COM servers

In certain situations, there may be a need to programmatically register or unregister a COM server
given just the name of the module that actually implements it. The specified server could be an
InProcess COM server or an OutOfProcess COM server. As we all know, inprocess COM servers are
registered by loading the DLL module and invoking the exported function DllRegisterServer().
The unregistration operation is performed by invoking DllUnregisterServer() instead.

OutOfProcess COM servers are registered by passing /REGSERVER on the command line for that executable.
The corresponding unregistration is done by passing /UNREGSERVER on the command line. Given this,
the only thing left is to detect if the file passed in is a DLL or an EXE.
This is easily achieved by using the GetFileVersionInfo() Platform SDK function.

I have written a C++ function to achieve all of this and the code for the same follows. This code uses
MFC but can be easily rewritten using std::basic_string() to make it usable within a pure ATL project.


HRESULT RegisterOleServer(const CString& strOleServerFile, bool bRegister)
{
CString strTempName = strOleServerFile;

DWORD dwFileType = VFT_UNKNOWN;

DWORD dwVerInfoBytes;
DWORD dwHandle;

LPBYTE pVerInfo = NULL;

VS_FIXEDFILEINFO* pFixedFileInfo = NULL;
UINT uiLength;

HRESULT hResult = S_OK;

// Detect if the server is an InProc or OutProc server.
dwVerInfoBytes = ::GetFileVersionInfoSize(strTempName.GetBuffer(0), &dwHandle);

if (dwVerInfoBytes == 0)
return HRESULT_FROM_WIN32(::GetLastError());

// Allocate memory to hold the version information for the specified file.
try
{
pVerInfo = new BYTE[dwVerInfoBytes];
}
catch(CMemoryException* e)
{
e->Delete();

return E_OUTOFMEMORY;
}

// Determine the server type.
if (::GetFileVersionInfo(strTempName.GetBuffer(0), 0, dwVerInfoBytes, pVerInfo) &&
::VerQueryValue(pVerInfo, _T(“\”), (LPVOID*)&pFixedFileInfo, &uiLength))
{
//if (AfxIsValidAddress(pFixedFileInfo, sizeof(VS_FIXEDFILEINFO)))
//{
dwFileType = pFixedFileInfo->dwFileType;
//}
}

// Cleanup resources allocated while determing the server type.
delete pVerInfo;

// Register the Ole Server depending on whether it is an Exe or Dll.
switch (dwFileType)
{
case VFT_APP:
{
CString strRegServerCommand;

if (bRegister)
strRegServerCommand.Format(_T(“%s /REGSERVER”), (LPCTSTR)strTempName);
else
strRegServerCommand.Format(_T(“%s /UNREGSERVER”), (LPCTSTR)strTempName);

// Code for ExecuteCommand() follows this function.
hResult = ExecuteCommand(strRegServerCommand, 10000);
}
break;

case VFT_DLL:
{
HINSTANCE hOleServerInst = NULL;

// Load the server dll into our process space.
hOleServerInst = ::LoadLibrary(strTempName);

if (hOleServerInst)
{
HRESULT (STDAPICALLTYPE *pfnRegServer)(void);

if (bRegister)
{
(FARPROC&)pfnRegServer = ::GetProcAddress(hOleServerInst, _T”DllRegisterServer”));

}
else
{
(FARPROC&)pfnRegServer = ::GetProcAddress(hOleServerInst, _T”DllUnregisterServer”));

}

if (pfnRegServer)
{
hResult = (*pfnRegServer)();
}
else
{
hResult = HRESULT_FROM_WIN32(::GetLastError());
}

::CoFreeLibrary(hOleServerInst);
}
else
{
hResult = HRESULT_FROM_WIN32(::GetLastError());
}
}
break;

default:
hResult = E_INVALIDARG;
break;
}

return hResult;
}

HRESULT ExecuteCommand(CString& strCommand, DWORD dwTimeout)
{
STARTUPINFO si;
PROCESS_INFORMATION pi;

HRESULT hResult = S_OK;

// Initialize start-up information for the new process.
::ZeroMemory(&si, sizeof(si));
si.cb = sizeof(si);

::ZeroMemory(&pi, sizeof(pi));

if (::CreateProcess(NULL, strCommand.GetBuffer(0), NULL, NULL, FALSE, NULL, NULL, NULL,
&si, &pi))
{
if (dwTimeout)
{
::WaitForSingleObject(pi.hProcess, dwTimeout);

::CloseHandle(pi.hProcess);
::CloseHandle(pi.hThread);
}
}
else
hResult = HRESULT_FROM_WIN32(::GetLastError());

return hResult;
}

More by Author

Must Read