WMI Client POC function for setting brightness

wmi-brightness.cpp

#include <objbase.h>
#include <windows.h>
#include <stdio.h>
#include <wbemidl.h>
#include <comdef.h>
#include <string>

#pragma comment(lib, "wbemuuid.lib")
#pragma comment(lib, "comsuppw.lib")

errno_t setScreenbrightness(int percent) {
    if (percent > 100 || percent < 0) {
        return E_INVALIDARG;
    }

    std::wstring percentWS = std::to_string(percent);

    // Pointers for accessing and calling the WMI service
    IWbemLocator*           pLocator    = NULL;
    IWbemServices*          pNamespace  = 0;
    IWbemClassObject*       pClass      = NULL;
    IWbemClassObject*       pInClass    = NULL;
    IWbemClassObject*       pInInst     = NULL;
    IEnumWbemClassObject*   pEnum       = NULL;

    // Result type for checking the process
    HRESULT hr = S_OK;

    BSTR path       = SysAllocString(L"root\\wmi");
    BSTR classPath  = SysAllocString(L"WmiMonitorbrightnessMethods");
    BSTR methodName = SysAllocString(L"WmiSetbrightness");
    BSTR timeout    = SysAllocString(L"Timeout");
    BSTR brightness = SysAllocString(L"Brightness");
    BSTR bstrQuery  = SysAllocString(L"Select * from WmiMonitorbrightnessMethods");

    if (!path || ! classPath || !methodName || ! timeout) {
        hr = ::GetLastError();
        goto cleanup;
    }

    // Initialize COM and connect up to CIMOM
    hr = CoInitialize(0);

    if (FAILED(hr)) {
        hr = ::GetLastError();
        goto cleanup;
    }

    //  NOTE:
    //  When using asynchronous WMI API's remotely in an environment where the "Local System" account
    //  has no network identity (such as non-Kerberos domains), the authentication level of
    //  RPC_C_AUTHN_LEVEL_NONE is needed. However, lowering the authentication level to
    //  RPC_C_AUTHN_LEVEL_NONE makes your application less secure. It is wise to
    //  use semi-synchronous API's for accessing WMI data and events instead of the asynchronous ones.
    hr = CoInitializeSecurity(
             NULL,
             -1,
             NULL,
             NULL,
             RPC_C_AUTHN_LEVEL_DEFAULT,
             RPC_C_IMP_LEVEL_IMPERSONATE,
             NULL,
             EOAC_NONE,
             NULL
         );

    if (FAILED(hr)) {
        hr = ::GetLastError();
        goto cleanup;
    }

    hr = CoCreateInstance(CLSID_WbemLocator,
                        0,
                        CLSCTX_INPROC_SERVER,
                        IID_IWbemLocator,
                        (LPVOID *) &pLocator);
    if (FAILED(hr)) {
        hr = ::GetLastError();
        goto cleanup;
    }

    hr = pLocator->ConnectServer(
             path,
             NULL,
             NULL,
             NULL,
             0,
             NULL,
             NULL,
             &pNamespace
         );

    if (hr != WBEM_S_NO_ERROR) {
        goto cleanup;
    }

    hr = CoSetProxyBlanket(
             pNamespace,
             RPC_C_AUTHN_WINNT,
             RPC_C_AUTHZ_NONE,
             NULL,
             RPC_C_AUTHN_LEVEL_CALL,
             RPC_C_IMP_LEVEL_IMPERSONATE,
             NULL,
             EOAC_NONE
         );

    if (hr != WBEM_S_NO_ERROR) {
        goto cleanup;
    }

    hr = pNamespace->ExecQuery(
             _bstr_t(L"WQL"),   // Query Language
             bstrQuery,         // Query to Execute
             WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY, // Make a semi-synchronous call
             NULL,              // Context
             &pEnum             // Enumeration Interface
         );

   if (hr != WBEM_S_NO_ERROR) {
       goto cleanup;
    }

    hr = WBEM_S_NO_ERROR;

    ULONG ulReturned;
    IWbemClassObject *pObj;
    DWORD retVal = 0;

    // Get the Next Object from the collection
    hr = pEnum->Next(
             WBEM_INFINITE, // timeout
             1,             // No of objects requested
             &pObj,         // Returned Object
             &ulReturned    // No of object returned
         );

    if (hr != WBEM_S_NO_ERROR) {
        goto cleanup;
    }

    // Get the class object
    hr = pNamespace->GetObject(classPath, 0, NULL, &pClass, NULL);
    if (hr != WBEM_S_NO_ERROR) {
        goto cleanup;
    }

    // Get the input argument and set the property
    hr = pClass->GetMethod(methodName, 0, &pInClass, NULL);
    if (hr != WBEM_S_NO_ERROR) {
        goto cleanup;
    }

    hr = pInClass->SpawnInstance(0, &pInInst);
    if (hr != WBEM_S_NO_ERROR) {
        goto cleanup;
    }

    VARIANT timeoutVar;
    VariantInit(&timeoutVar);

    V_VT(&timeoutVar)   = VT_BSTR;
    V_BSTR(&timeoutVar) = SysAllocString(L"0");
    hr = pInInst->Put(
             timeout,
             0,
             &timeoutVar,
             CIM_UINT32
         );

    VariantClear(&timeoutVar);
    if (hr != WBEM_S_NO_ERROR) {
        goto cleanup;
    }

    VARIANT brightVar;
    VariantInit(&brightVar);

    V_VT(&brightVar) = VT_BSTR;
    // V_BSTR(&brightVar) = SysAllocString(L"100");
    V_BSTR(&brightVar) = percentWS.c_str();
    hr = pInInst->Put(brightness, 0, &brightVar, CIM_UINT8);

    VariantClear(&brightVar);

    if (hr != WBEM_S_NO_ERROR) {
        goto cleanup;
    }

    VARIANT pathVariable;
    VariantInit(&pathVariable);

    hr = pObj->Get(
             _bstr_t(L"__PATH"),
             0,
             &pathVariable,
             NULL,
             NULL
         );

    if (hr != WBEM_S_NO_ERROR) {
        goto cleanup;
    }

    hr = pNamespace->ExecMethod(
             pathVariable.bstrVal,
             methodName,
             0,
             NULL,
             pInInst,
             NULL,
             NULL
         );

    VariantClear(&pathVariable);

    if (hr != WBEM_S_NO_ERROR) {
        goto cleanup;
    }

// Free up resources
cleanup:
    SysFreeString(path);
    SysFreeString(classPath);
    SysFreeString(methodName);
    SysFreeString(timeout);
    SysFreeString(brightness);
    SysFreeString(bstrQuery);

    if (pClass) pClass->Release();
    if (pInInst) pInInst->Release();
    if (pInClass) pInClass->Release();
    if (pLocator) pLocator->Release();
    if (pNamespace) pNamespace->Release();

    CoUninitialize();

    return hr;
}