Windows: Calling a WMI function using FreePascal -- Working example? - winapi

Question

I am looking for sample code on how to call a WMI function. Does anyone has a working example in FreePascal, ideally including code on how to pass parameters to the function? Unfortunately, the "Delphi WMI code Creator" does not help me as the FreePascal code for creating a function does not work.
Just to be clear: This is not about querying WMI properties, but calling a function like Win32_Printer.AddPrinterConnection (just to name an example).

Answer 1

I found a piece of Delphi code that set up many of the standard objects in the same way as Drake Wu's C++ example did.
I was interested in that example because I'm interested in edids, so I fully translated said C++ article's solution to Delphi/FPC. It seems to work.
program wmiedidint2;
// based on https://theroadtodelphi.com/2011/04/21/accesing-the-wmi-from-delphi-and-fpc-via-com-without-late-binding-or-wbemscripting_tlb/
// modified to function as https://learn.microsoft.com/en-us/answers/questions/95631/wmi-c-application-problem-wmimonitordescriptormeth.html?childToView=96407#answer-96407
{$IFDEF FPC}
{$MODE DELPHI} {$H+}
{$ENDIF}
{$APPTYPE CONSOLE}
uses
Windows,
Variants,
SysUtils,
ActiveX,
JwaWbemCli;
const
RPC_C_AUTHN_LEVEL_DEFAULT = 0;
RPC_C_IMP_LEVEL_IMPERSONATE = 3;
RPC_C_AUTHN_WINNT = 10;
RPC_C_AUTHZ_NONE = 0;
RPC_C_AUTHN_LEVEL_CALL = 3;
EOAC_NONE = 0;
function GetBytesFromVariant(const V: Variant): TBytes;
// this function is a mess and only works for bytes. From SO
var
Len: Integer;
SafeArray: PVarArray;
begin
Len := 1+VarArrayHighBound(v, 1)-VarArrayLowBound(v, 1);
SetLength(Result, Len);
SafeArray := VarArrayAsPSafeArray(V);
Move(SafeArray.Data^, Pointer(Result)^, Length(result)*SizeOf(result[0]));
end;
procedure Test_IWbemServices_ExecQuery;
const
strLocale = '';
strUser = '';
strPassword = '';
strNetworkResource = 'root\WMI';
strAuthority = '';
WQL = 'SELECT * FROM WmiMonitorDescriptorMethods';
EDIDMethodname = 'WmiGetMonitorRawEEdidV1Block';
EDIDClassName = 'WmiMonitorDescriptorMethods';
var
FWbemLocator : IWbemLocator;
FWbemServices : IWbemServices;
FUnsecuredApartment : IUnsecuredApartment;
ppEnum : IEnumWbemClassObject;
apObjects : IWbemClassObject;
puReturned : ULONG;
pVal : OleVariant;
pType : Integer;
plFlavor : Integer;
Succeed : HRESULT;
varreturnvalue : olevariant;
varotherval : longint;
varcmd2 : tagVariant;
varcommand : olevariant; // tagVARIANT;
pOutParamsDefinition,
pInParamsDefinition,
pClass,
pClassInstance : IWbemClassObject;
callres : IWbemCallResult;
err : IErrorInfo;
aname,w2 : Widestring;
bytes : TBytes;
i : integer;
procedure teststatus(const msg:string);
begin
if Succeeded(succeed) then
writeln('Successs:',msg)
else
writeln('Fail:',msg)
end;
begin
// Set general COM security levels --------------------------
// Note: If you are using Windows 2000, you need to specify -
// the default authentication credentials for a user by using
// a SOLE_AUTHENTICATION_LIST structure in the pAuthList ----
// parameter of CoInitializeSecurity ------------------------
if Failed(CoInitializeSecurity(nil, -1, nil, nil, RPC_C_AUTHN_LEVEL_DEFAULT, RPC_C_IMP_LEVEL_IMPERSONATE, nil, EOAC_NONE, nil)) then Exit;
// Obtain the initial locator to WMI -------------------------
if Succeeded(CoCreateInstance(CLSID_WbemLocator, nil, CLSCTX_INPROC_SERVER, IID_IWbemLocator, FWbemLocator)) then
try
// Connect to WMI through the IWbemLocator::ConnectServer method
if Succeeded(FWbemLocator.ConnectServer(strNetworkResource, strUser, strPassword, strLocale, WBEM_FLAG_CONNECT_USE_MAX_WAIT, strAuthority, nil, FWbemServices)) then
try
// Set security levels on the proxy -------------------------
if Failed(CoSetProxyBlanket(FWbemServices, RPC_C_AUTHN_WINNT, RPC_C_AUTHZ_NONE, nil, RPC_C_AUTHN_LEVEL_CALL, RPC_C_IMP_LEVEL_IMPERSONATE, nil, EOAC_NONE)) then Exit;
if Succeeded(CoCreateInstance(CLSID_UnsecuredApartment, nil, CLSCTX_LOCAL_SERVER, IID_IUnsecuredApartment, FUnsecuredApartment)) then
try
// Use the IWbemServices pointer to make requests of WMI
//Succeed := FWbemServices.ExecQuery('WQL', WQL, WBEM_FLAG_FORWARD_ONLY OR WBEM_FLAG_RETURN_IMMEDIATELY, nil, ppEnum);
Succeed := FWbemServices.ExecQuery('WQL', WQL, WBEM_FLAG_FORWARD_ONLY, nil, ppEnum);
if Succeeded(Succeed) then
begin
Writeln('Running Wmi Query..Press Enter to exit');
// Get the data from the query
while (ppEnum.Next(WBEM_INFINITE, 1, apObjects, puReturned)=0) do
begin
succeed:= apObjects.Get('__PATH', 0, pVal, pType, plFlavor);
teststatus('get __PATH');
aname:=pval;
writeln('__PATH: ',aname);
succeed:=fwbemservices.GetObject(edidclassname,0,nil,pClass,callres);
teststatus('getobject');
succeed:=pClass.GetMethod(EDIDMethodname,0,pInParamsDefinition,pOutParamsDefinition);
teststatus('getmethod');
succeed:=pInParamsDefinition.SpawnInstance(0, pClassInstance);
teststatus('Spawn');
fillchar(varcmd2,sizeof(varcommand),#0);
varcmd2.vt:=VT_UI1;
varcmd2.bval:=0;
move(varcmd2,varcommand,sizeof(varcmd2));
succeed:= pClassInstance.Put('BlockId',0,#VarCommand,0);
teststatus('put blockid');
writeln('The BlockId is: ,',varCommand);
pOutParamsDefinition:=Nil;
callres:=nil;
w2:=EDIDMethodname;
succeed:= fwbemservices.ExecMethod(aname,w2,0,nil,pClassInstance,pOutParamsDefinition,callres);
if succeeded(succeed) then
begin
writeln('execute success!');
end;
succeed:= pOutParamsDefinition.Get('BlockType', 0, varreturnvalue,ptype,plFlavor);
if succeeded(succeed) then
begin
writeln('blocktype:',varreturnvalue);
varotherval:=varreturnvalue;
if varotherval=1 then
begin
succeed:= pOutParamsDefinition.Get('BlockContent', 0, varreturnvalue,ptype,plFlavor);
if succeeded(succeed) then
begin
bytes:=GetBytesFromVariant(varreturnvalue);
write('bytes:');
for i:=0 to length(bytes)-1 do
begin
write('$',inttohex(bytes[i],2),' ');
end;
writeln;
end;
end;
end;
end;
end
else
Writeln(Format('Error executing WQL sentence %x',[Succeed]));
finally
FUnsecuredApartment := nil;
end;
finally
FWbemServices := nil;
end;
finally
FWbemLocator := nil;
end;
end;
begin
// Initialize COM. ------------------------------------------
if Succeeded(CoInitializeEx(nil, COINIT_MULTITHREADED)) then
try
Test_IWbemServices_ExecQuery;
finally
CoUninitialize();
end;
Readln;
end.
Note that the original (roadtodelphi) page also demonstrates event sinks

Answer 2

To call a WMI function, you need to:
Get the WMI class from IWbemServices.GetObject(ClassName)
Call IWbemClassObject.GetMethod(MethodName) to get the parameter information(In and Out Params) of the function
Pass the required value to the corresponding through a VARIANT: IWbemClassObject.Put("Name",VARIANT). Maybe just do this in pascal: objInParams.Properties_.Item('Name').Value := xxx;
Get an instance of the class and get its Object Path, and finally execute IWbemServices.ExecMethod(path,MethodName,objInParams,objOutParams).
There is also a C++ sample with WmiMonitorDescriptorMethods.WmiGetMonitorRawEEdidV1Block here, although I am not familiar with FreePascal, you could also follow the steps and convert it to FreePascal.