WSH and clipboard access

I did some Windows Script Host programming recently and I was pleasantly surprised by its power, features and flexibility. One thing that I couldn't accomplish was accessing the clipboard from WSH. Digging the internet I found some solutions like this one based on Internet Explorer Automation. There are several problems with this approach as you can read in my article about Internet Explorer Automation: What's wrong with Internet Explorer Automation?

My solution for scripting the clipboard content in WSH is a regular COM object created with VC++ and ATL.

Download full source code and compiled DLL: WSH_clipboard.zip
To install the COM object run register.bat

I found scripting the clipboard useful enough to add this feature to the next release of Twebst Web Automation Library.

IHTMLDocument3::getElementsByTagName and IHTMLElementCollection

A common task when writing Internet Explorer extensions is to browse a collection of objects based on a specified element tag-name. To work with collections IE provides IHTMLElementCollection interface that represents a collection of elements in an HTML document.

Usually a collection is retrieved by calling methods of IHTMLDocument2 interface. For some tag-names there specialized methods to retrieve collection (IHTMLDocument2::get_anchors , IHTMLDocument2::get_applets, IHTMLDocument2::get_forms, IHTMLDocument2::get_images, IHTMLDocument2::get_links, IHTMLDocument2::get_scripts).

To get all elements collection there is IHTMLDocument2::get_all.
One way to get a collection of elements having a specified tag-name is:

// CComQIPt<IHTMLDocument2> spDocument is a document object.

CComQIPtr<IHTMLElementCollection> spAllCollection;
HRESULT hRes = spDocument->get_all(&spAllCollection);
_ASSERTE(SUCCEDED(hRes) && (spAllCollection != NULL));

// Get the sub-collection of elements that have the "input" tag name.
CComVariant varTagName(CComBSTR("input"));
CComQIPtr<IDispatch> spDispCollection;
hRes = spAllCollection->tags(varTagName, &spDispCollection);

CComQIPtr<IHTMLElementCollection> spInputCollection = spDispCollection;
_ASSERTE(spInputCollection != NULL);

// Now you can browse spInputCollection using
// IHTMLElementCollection::item and IHTMLElementCollection::get_length methods.

The second method is:

// CComQIPt spDocument is a document object.
// Query for IHTMLDocument3 interface
CComQIPtr<IHTMLDocument3> spDoc3 = spDocument;
_ASSERTE(spDoc3 != NULL);

// Get the collection of elements that have the "input" tag name.
CComQIPtr<IHTMLElementCollection> spInputCollection;
HRESULT hRes = spDoc3->getElementsByTagName(CComBSTR("input"), &spInputCollection);
_ASSERTE(SUCCEDEED(hRes));

// Now you can browse spInputCollection using
// IHTMLElementCollection::item and IHTMLElementCollection::get_length methods.

ATL thunks and Windows DEP story

When using older ATL versions the program may generate an access violation due to Data Execution Prevention. This is basically a memory protection feature that prevents executing code from memory pages marked as non-executable.

The ATL implementation of CWindow class uses a technique called thunk. A thunk is a small piece of code that ATL generates in a region of memory allocated on the heap. Older versions of ATL did not set the execution flag on the allocated memory pages and that generates a crash on Windows machines where DEP is enabled.

Usually ATL is used in Internet Explorer extensions. If DEP is enabled then the result is a browser crash. This is a good reason to upgrade to Visual Studio 2005 or later. Find more on how to activate DEP in IE7 here.

ATL + STL = CAdapt

I didn't know about CAdapt class until I tried to convert a VS2003 project to VS2005. Everything worked OK but I couldn't compile it! The compiler complained about:

std::list<CComQIPtr<IHTMLElement> >.

I found that what was accepted by VC++ 2003 compiler is not accepted by VC++ 2005 compiler. The reason of for is the address operator overloaded by CComQIPtr class. std::list class needs the address of a CComQIPtr object but & operator returns a IHTMLElement* address.

Here's where CAdapt class comes to save us. The list of smart pointers becomes: std::list<CAdapt<CComQIPtr<IHTMLElement> > >
Also you need to use m_T member where needed.

When IHTMLWindow2.document throws UnauthorizedAccessException

This is basically a C# translation of one of my older articles "When IHTMLWindow2::get_document returns E_ACCESSDENIED". Some .Net people encountered difficulties to use it, so I decided to make their life easier.

The main problem is the confusion created by System.IServiceProvider .Net interface because it has the same name as the COM interface. Once this issue is passed the code translation is straightforward. Here's the interop code to declare the COM interface IServiceProvider.

// This is the COM IServiceProvider interface, not System.IServiceProvider .Net interface!
[ComImport(), ComVisible(true), Guid("6D5140C1-7436-11CE-8034-00AA006009FA"),
InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
public interface IServiceProvider
{
   [return: MarshalAs(UnmanagedType.I4)][PreserveSig]
   int QueryService(ref Guid guidService, ref Guid riid, [MarshalAs(UnmanagedType.Interface)] out object ppvObject);
}

You find here full source code of the sample assembly.

This technique was successfully implemented and tested in Twebst web automation library.

How to get a handle to current TabWindowClass tab in IE7

IWebBrowser2::get_HWND method gets the handle of the Internet Explorer 7 main window. Sometimes the tab window handle is needed. Here's a sample code that I recently found in MSDN. It shows how to get the handle of the tab window starting from a IWebBrowser2 object.

#include <shlguid.h>

HWND GetTabWnd(CComQIPtr<IWebBrowser2> spBrowser)
{
     HWND hwndTab = NULL;
     CComQIPtr<IServiceProvider> spServiceProvider = spBrowser;

     if (spServiceProvider != NULL)
     {
          CComQIPtr<IOleWindow> spWindow;
          if (SUCCEEDED(spServiceProvider->QueryService(
                         SID_SShellBrowser,
                              IID_IOleWindow,
                              (void**)&spWindow)))
          {
             
               spWindow->GetWindow(&hwndTab));
          }
     }

     return hwndTab;
}

I think the code is supposed to work on top level IWebBrowser2 objects. You can read more about top browser objects in my previous article.

This technique was successfully implemented and tested in Twebst web automation library.

When IWebBrowser2::get_HWND returns E_FAIL

IWebBrowser2::get_HWND "gets the handle of the Microsoft Internet Explorer main window". As any COM method get_HWND returns a HRESULT value. According to MSDN, the method "returns S_OK if successful, or an error value otherwise".

It was hard for me to imagine how this method could fail but I still got an E_FAIL return value. This happened because the IWebBrowser2 object was not the top level browser. A web page containing frames/iframes is represented by a hierarchy of IHTMLWindow objects. Each window has an associated IHTMLDocument2 object exposed by IHTMLWindow2::get_document. An IHTMLWindow can be also converted to a IWebBrowser2 object. Here's my solution to get the main window handle starting from a non-top level browser object (this is a common scenario when adding your custom menu item in the IE context menu).

// IHTMLWindow2 to IWebBrowser2
CComQIPtr<IWebBrowser2> IHTMLWindow2ToIWebBrowser2(CComQIPtr<IHTMLWindow2> spHTMLWindow)
{
     ATLASSERT(spHTMLWindow != NULL);

     // Query for a service provider.
     CComQIPtr<IWebBrowser2>     spBrowser;
     CComQIPtr<IServiceProvider> spServiceProvider = spHTMLWindow;

     if (spServiceProvider != NULL)
     {
          // Ask the service provider for a IWebBrowser2 object.
          spServiceProvider->QueryService(IID_IWebBrowserApp, IID_IWebBrowser2, (void**)&spBrowser);
     }

     return spBrowser;
}

// IWebBrowser2 to IHTMLWindow2
CComQIPtr<IHTMLWindow2> IWebBrowserToIHTMLWindow(CComQIPtr<IWebBrowser2> spBrowser)
{
     ATLASSERT(spBrowser != NULL);
     CComQIPtr<IHTMLWindow2> spWindow;

     // Get the document of the browser.
     CComQIPtr<IDispatch> spDisp;
     spBrowser->get_Document(&spDisp);

     // Get the window of the document.
     CComQIPtr<IHTMLDocument2> spDoc = spDisp;
     if (spDoc != NULL)
     {
          spDoc->get_parentWindow(&spWindow);
     }

     return spWindow;
}


CComQIPtr<IWebBrowser2> TopBrowser(CComQIPtr<IWebBrowser2> spBrowser)
{
     ATLASSERT(spBrowser != NULL);

     // Retrieve IHTMLWindow2 from browser.
     CComQIPtr<IHTMLWindow2> spHTMLWnd = IWebBrowserToIHTMLWindow(spBrowser);
     if (spHTMLWnd != NULL)
     {
          // Find top window.
          CComQIPtr<IHTMLWindow2> spTopWindow;
          HRESULT hResult = spHTMLWnd->get_top(&spTopWindow);

          if (SUCCEEDED(hResult) && (spTopWindow != NULL))
          {
               // Convert the browser object to window.

               return IHTMLWindow2ToIWebBrowser2(spTopWindow);
          }
     }

     return CComQIPtr<IWebBrowser2>();
}

This technique was successfully implemented and tested in My web automation library.
codeproject

When IHTMLWindow2::get_document returns E_ACCESSDENIED

Internet Explorer extensions usually needs to access HTML elements. When extensions are initialized they get a IWebBrowser2 pointer representing the browser. Starting with this pointer one can get any HTML element in the web page but to do that we need to browse a hierarchy of frames first. The simplest web pages only have one frame and one document. Web pages containing <frame> or <iframe> have a hierarchy of frames, each frame having its own document.

Here are the objects involved and the corresponding interfaces:

browser      - IWebBrowser2
frame/iframe - IHTMLWindow2
document     - IHTMLDocument2
element      - IHTMLElement

The list bellow shows what method to call to get one object from another:

browser      -> document        IWebBrowser2::get_Document
document     -> frame           IHTMLDocument2::get_parentWindow
frame        -> document        IHTMLWindow2::get_document
frame        -> parent frame    IHTMLWindow2::get_parent
frame        -> children frames IHTMLWindow2::get_frames

A normal call chain to get a HTML element is:

browser -> document -> frame -> child frame -> ... -> child frame -> document -> element

This will work almost all the time. The problems arise when different frames contain documents loaded from different internet domains. In this case IHTMLWindow2::get_document returns E_ACCESSDENIED when trying to get the document from the frame object. I think this happens to prevent cross frame scripting atacks.

Here is HtmlWindowToHtmlDocument function I wrote to be used instead IHTMLWindow2::get_document to bypass the restriction:




// Converts a IHTMLWindow2 object to a IHTMLDocument2. Returns NULL in case of failure.
// It takes into account accessing the DOM across frames loaded from different domains.
CComQIPtr<IHTMLDocument2> HtmlWindowToHtmlDocument(CComQIPtr<IHTMLWindow2> spWindow)
{
     ATLASSERT(spWindow != NULL);

     CComQIPtr<IHTMLDocument2> spDocument;
     HRESULT hRes = spWindow->get_document(&spDocument);
    
     if ((S_OK == hRes) && (spDocument != NULL))
     {
          // The html document was properly retrieved.
          return spDocument;
     }

     // hRes could be E_ACCESSDENIED that means a security restriction that
     // prevents scripting across frames that loads documents from different internet domains.
     CComQIPtr<IWebBrowser2>  spBrws = HtmlWindowToHtmlWebBrowser(spWindow);
     if (spBrws == NULL)
     {
          return CComQIPtr<IHTMLDocument2>();
     }

     // Get the document object from the IWebBrowser2 object.
     CComQIPtr<IDispatch> spDisp;
     hRes = spBrws->get_Document(&spDisp);
     spDocument = spDisp;

     return spDocument;
}


// Converts a IHTMLWindow2 object to a IWebBrowser2. Returns NULL in case of failure.
CComQIPtr<IWebBrowser2> HtmlWindowToHtmlWebBrowser(CComQIPtr<IHTMLWindow2> spWindow)
{
     ATLASSERT(spWindow != NULL);

     CComQIPtr<IServiceProvider>  spServiceProvider = spWindow;
     if (spServiceProvider == NULL)
     {
          return CComQIPtr<IWebBrowser2>();
     }

     CComQIPtr<IWebBrowser2> spWebBrws;
     HRESULT hRes = spServiceProvider->QueryService(IID_IWebBrowserApp, IID_IWebBrowser2, (void**)&spWebBrws);
     if (hRes != S_OK)
     {
          return CComQIPtr<IWebBrowser2>();
     }

     return spWebBrws;
}

Here is the C# version of the code: "When IHTMLWindow2.document throws UnauthorizedAccessException".

This technique was successfully implemented and tested in My web automation library.
codeproject

COM number speller

Some time ago, I was asked to provide a way to print numbers as text in Romanian language. Interestingly, I couldn't find an easy way to do this in Excel (Office 2003 as far as I remember). Searching the internet, I found other people having the same problem. Microsoft provides a solution for English language, but not for Romanian.

I decided to create a reusable piece of code that will be easily used in as many environments as possible. I chose COM and ATL to be the solution to my problem. This is also a good programming exercise for my rusty COM / C++ skills and I plan to use it as a template for all my future COM objects.

Points of interest:

• error info support by implementing IErrorInfo interface.
• Help in CHM format and context identifiers specified in MIDL source file.
• BSTR manipulation using CComBSTR class provided by ATL.
• IDispatch support, so the component can be used from scripting environments.
  
• Spelling implementation itself and support for multiple languages (only Romanian and English for now).

To install the COM object just simply run Install.bat
Here is the Excel macro that makes use of NumberSpeller COM object:

Function Spell(n As Currency) As String
'Create the speller object.
Dim s As NumberSpellerLib.speller
Set s = New NumberSpellerLib.speller

Dim o As Object
Set o = s
o.Language = "ro"
Spell = o.Translate(n)
End Function

Downloads:

• full source code, compiled DLL and CHM help: NumberSpeller.zip
  
• C++ sample code: NumberSpellerSample1.zip
  
• Excel sample file: NumberSpellerSample2.zip
  
• JS sample file: NumberSpellerSample3.zip