How do I enumerate all properties of a Variant?

[Phil Brinkle 0]

Greetings!

 

I am working with an undocumented third-party COM server via WMI interface.

var
  ACPIObj : ISWbemObject;
  DataPackProp : ISWbemProperty;
  OutParam: ISWbemObject;
  PropValue : Variant;
begin
//...
OutParam:=ACPIObj.ExecMethod_('GetObjectData', nil, 0, nil);
if OutParam <> nil then begin
  DataPackProp:=OutParam.Properties_.Item('DataPack’,0);
  PropValue:=DataPackProp.Get_Value;
//..
end;

After executing a method called ‘GetObjectData’, PropValue is actually storing an IDispatch interface, since it has the VarType of varDispatch. Is there a way of enumerating all the properties stored in the PropValue variable?

 

Thank you!

[FPiette 383]

Yes, you can.

Basically, you have to call GetTypeInfoCount(), GetTypeInfo(), GetTypeAttr() and other functions (All documented by Microsoft).

Here is a function to list all method names including property getter/setter. Similar code can enumerate argument list, argument data types and return value data type.

 

procedure DisplayMethodNames(
    const DispIntf : IDispatch;
    const IntfName : String;
    Strings        : TStrings);
var
    Count            : Integer;
    TypeInfo         : ITypeInfo;
    TypeAttr         : PTypeAttr;
    FuncDesc         : PFuncDesc;
    HR               : HRESULT;
    I                : Integer;
    FuncName         : WideString;
begin
    if IntfName <> '' then
        Strings.Add(IntfName);

    Count := 0;
    HR := DispIntf.GetTypeInfoCount(Count);
    if Failed(HR) or (Count = 0) then
        Exit;

    HR := DispIntf.GetTypeInfo(0, 0, TypeInfo);
    if Succeeded(HR) and (TypeInfo <> nil) then begin
        TypeAttr := nil;
        HR       := TypeInfo.GetTypeAttr(TypeAttr);
        if Succeeded(HR) and (TypeAttr <> nil) then begin
            for I := 0 to TypeAttr.cFuncs - 1 do begin
                FuncDesc := nil;
                HR       := TypeInfo.GetFuncDesc(I, FuncDesc);
                if Succeeded(HR) and (FuncDesc <> nil) then begin
                    TypeInfo.GetDocumentation(FuncDesc.memid,
                                              @FuncName,
                                              nil,  // DocString,
                                              nil,  // HelpContext
                                              nil); // HelpFile
                    if Length(FuncName) <> 0 then
                        Strings.Add(Format('  %-3d %s', [I, FuncName]));
                    TypeInfo.ReleaseFuncDesc(FuncDesc);
                end;
            end;
            TypeInfo.ReleaseTypeAttr(TypeAttr);
        end;
    end;
end;

 

Edited October 28, 2020 by FPiette

[Phil Brinkle 0]

Thank you for your quick reply, sir!

 

Your code works fine and it returns 36 functions for me:

  0   QueryInterface
  1   AddRef
  2   Release
  3   GetTypeInfoCount
  4   GetTypeInfo
  5   GetIDsOfNames
  6   Invoke
  7   Put_
  8   PutAsync_
  9   Delete_
  10  DeleteAsync_
  11  Instances_
  12  InstancesAsync_
  13  Subclasses_
  14  SubclassesAsync_
  15  Associators_
  16  AssociatorsAsync_
  17  References_
  18  ReferencesAsync_
  19  ExecMethod_
  20  ExecMethodAsync_
  21  Clone_
  22  GetObjectText_
  23  SpawnDerivedClass_
  24  SpawnInstance_
  25  CompareTo_
  26  Qualifiers_
  27  Properties_
  28  Methods_
  29  Derivation_
  30  Path_
  31  Security_
  32  Refresh_
  33  SystemProperties_
  34  GetText_
  35  SetFromText_

Now I have to examine it to know how to retrieve all the properties of an IDispatch interface, since I am not familiar with COM programming. Thank you for you help!

 

[FPiette 383]

Thanks. If you like my answer, please mark it as such (The heart icon on the right side of my answer).

Maybe you have a type library ? If you import it into Delphi, you'll have all the information.

 

Edited October 28, 2020 by FPiette

[Guest]

4 hours ago, FPiette said:

Thanks. If you like my answer, please mark it as such (The heart icon on the right side of my answer).

Mr. Piette! I now have a go-to-guy re COM/OLE 🙂

Seriously, don't worry, i avoid OLE like i do Covid.

Ahem, not true, i'm more afraid of OLE than Covid.

'll give you one anyways!

Hmm.. still above you 🙂 la-di-da... (not for long though, deep into deliveries for at least ½ a year on)...

[Phil Brinkle 0]

On 10/28/2020 at 7:15 PM, FPiette said:

Thanks. If you like my answer, please mark it as such (The heart icon on the right side of my answer).

Maybe you have a type library ? If you import it into Delphi, you'll have all the information.

 

I am sorry, I don't have one, since I am working with an undocumented COM server.

 

BTW, experimentally I found out that the PropValue variable has one property of Result which is an array of bytes. So, using TempArrayBuffer:=PropValue.Result I can read the content of the array. Do you know the way of enumerating all the properties of the PropValue variant? I believe there should be other properties. Thank you!

Edited October 30, 2020 by Phil Brinkle

[Anders Melander 1784]

On 10/28/2020 at 10:02 PM, Dany Marmur said:

Seriously, don't worry, i avoid OLE like i do Covid.

Maybe if you learned the difference between OLE and COM you wouldn't be so scared... Hardly anyone uses OLE anymore.

[FPiette 383]

44 minutes ago, Phil Brinkle said:

I am working with an undocumented COM server.

Undocumented doesn't mean it has not documentation inside the exe/dll. The proof is that my function show the list of functions. Try to import the DLL in Delphi as it is a type library (Delphi Menu Component / Import component / Import a Type Library. If it doesn't appear in the list, click the Add button and select your  dll. If it doesn't work, try adding it as an ActiveX instead.

[Anders Melander 1784]

On 10/28/2020 at 4:45 PM, Phil Brinkle said:

Your code works fine and it returns 36 functions for me

Those are just the WMI methods and they are all documented.

https://docs.microsoft.com/en-us/windows/win32/api/wbemcli/nn-wbemcli-iwbemclassobject

 

If you want to talk to a COM server why are you then going through WMI? Are you sure it isn't a WMI Provider you are talking about?

 

52 minutes ago, Phil Brinkle said:

I am working with an undocumented COM server.

If you install the Windows SDK (just the tools parts) there's a utility in it called OleView that you can use to examine type libraries and COM servers.

 

The type library of your server is probably embedded in the EXE file.

 

Edit: If it's a WMI provider then it's probably a DLL and it's probably early bound and without a type library. It depends on what kind of provider it is.

Edited October 30, 2020 by Anders Melander

[Anders Melander 1784]

Instead of waiting on the back and forth I'll assume that what we have here is a classic case of the XY problem.

 

To determine what properties a WMI object exposes you can use a tool like WMI Explorer (there are many other tools like that, this is just the first one I found).

[Phil Brinkle 0]

It's a BIOS ACPI object which can be accessed through WMI (root/wmi namespace) only. WMI Explorer is a very good software since it lets me execute methods of objects. I have been using it for months, thanks! But it cannot pass an array of values to a WMI method, only an integer.

 

Anyway, I much appreciate your assistance, guys!