MeowMoniker ReadMe

Overview

MeowMoniker and Feline are COM objects designed and built by Chris Sells, with a great deal of input from Don Box and Tim Ewald. The MeowMoniker is a custom moniker derived from the CComMoniker class implemented by Don Box, Tim Ewald and Chris Sells.

To contact the authors with suggestions or comments, use csells@sellsbrothers.com, tewald@obelisk-llc.com and dbox@microsoft.com.

MeowMoniker Usage

Microsoft tags every marshalled interface reference packet with the signature MEOW (which they claim stands for Microsoft Extended Object Wire-representation). This binary packet is a serialized interface reference used for inter-apartment activation. Turning this binary packet into a string (via some encoding technique, i.e. Base64) allows a serialized interface pointer to be passed more easily than binary data, e.g. as a command-line argument or in an HTML page.

Monikers, on the other hand, provide a general-purpose way for a client to separate itself from the object binding policy. These object binding polices can be composed and stored in strings. These strings contain a string description of the binding policy and policy parameters. By building a custom moniker that takes a string-ized interface reference as a parameter, a client can use the standard moniker-based binding algorithm and bind to a running object via an interface reference. The MeowMoniker is an implementation of a moniker that can compose display names out of interface pointers and bind to objects via its display names.

To create a MeowMoniker from an interface pointer, MeowMoniker.dll exposes the CreateMeowMoniker() function:

STDAPI CreateMeowMoniker( IUnknown* punk, // Pointer to the interface to be marshaled REFIID riid, // Reference to the identifier of the interface DWORD dwDestContext, // Destination context DWORD mshlflags, // Reason for marshaling IMoniker** ppmk); // Indirect pointer to the moniker


        
            e.g.
        
        
            IMoniker* pmk;
            

            hr = CreateMeowMoniker(punkObject,
            

                    
                   IID_IUnknown,
            

                    
                   MSHCTX_DIFFERENTMACHINE,
            

                    
                   MSHLFLAGS_NORMAL,
            

                    
                   &pmk);

To obtain the MeowMoniker's display name, use the GetDisplayName() member function of the IMoniker interface:

HRESULT GetDisplayName( IBindCtx *pbc, // Pointer to bind context to be used IMoniker *pmkToLeft, // Pointer to moniker to the left in the composite LPOLESTR *ppszDisplayName); //Indirect pointer to the display name


        
            e.g.
        
        
            IBindCtx* pbc;
            

            hr = CreateBindCtx(0, &pbc);
            

            wchar_t* pwszDisplayName;
            

            hr = pmk->GetDisplayName(pbc, 0, &pwszDisplayName);

To parse a display name composed by the MeowMoniker, OLE32.dll exposes the MkParseDisplayName() function:

WINOLEAPI MkParseDisplayName( LPBC pbc, // Pointer to the bind context object LPCOLESTR szUserName, // Pointer to display name ULONG FAR *pchEaten, // Pointer to the number of characters consumed LPMONIKER FAR *ppmk); // Indirect pointer to the moniker


        
            e.g.
        
        
            IBindCtx* pbc;
            

            hr = CreateBindCtx(0, &pbc);
            

            IMoniker* pmk;
            

            ULONG cchEaten;
            

            hr = MkParseDisplayName(pbc,
            

                 pwszDisplayName,
            

                 &pmk);

To bind to a object, use the BindToObject() member function of the IMoniker interface:

HRESULT BindToObject( IBindCtx *pbc, // Pointer to bind context object to be used IMoniker *pmkToLeft, // Pointer to moniker that precedes this one in the composite REFIID riidResult, // IID of interface pointer requested void **ppvResult); // Indirect pointer to the specified interface on the object


        
            e.g.

IUnknown* punk; hr = pmk->BindToObject(pbc, 0, IID_IUnknown, (void**)&punk);
Note: The MeowMoniker does not current support composition or the IMoniker interface member function BindToStorage().

Feline Usage

Since neither VB nor VBScript supports calling CreateMeowMoniker() and since VBScript has no equivalent of the VB function GetObject(), the Feline object provides a dual-interface for making display names out of interface pointers and parsing moniker display names:

[ object, uuid(CB18CB8E-C7CC-11D0-9A44-00008600A105), dual, helpstring("DIFeline Interface"), pointer_default(unique) ] interface DIFeline : IDispatch { [id(1), helpstring("Returns the Meow Moniker name of an interface pointer")] HRESULT GetDisplayName([in] IDispatch* pdisp, [out, retval] BSTR* pbstrName); [id(2), helpstring("Returns an interface pointer given any moniker display name")] HRESULT ParseDisplayName([in] BSTR bstrName, [out, retval] IDispatch** ppdisp); };

The following is an example Active Server Page that creates an object on the server, creates a display name using the object's interface pointer and uses the display name to create a client-side script. The client-side script uses its own instance of a feline object to parse the display name and bind to the object created on the server-side.

<HEAD> <TITLE>feline.asp</TITLE> </HEAD> <BODY>


        
            <object classid="clsid:CB18CB8F-C7CC-11D0-9A44-00008600A105"
            

               runat=server
            

               id=feline>
            

            </object>
        
        
            <object classid="clsid:7CF322E0-29A9-11D0-B367-0080C7BC7884"
            

               runat=server
            

               id=pt>
            

            </object>
        
        
            <object classid="clsid:CB18CB8F-C7CC-11D0-9A44-00008600A105"
            

               id=feline>
            

            </object>
        
        
            <script language=vbscript>
            

               dim pt
            

               set pt = feline.ParseDisplayName("<%= 
            feline.GetDisplayName(pt) %>")
            

               pt.x = 100
            

               pt.y = 200
            

               document.write pt.x & ", " & pt.y
            

            </script>

</BODY> </HTML>

CComMoniker Implementation

The MeowMoniker derives most of its functionality from CComMoniker, provided in mkbase.h and mkbase.cpp. This base class implements IMoniker, IParseDisplayName, IROTData and IMarshal (for marshal-by-value). This implementation uses the moniker's display name as the persistent state. The custom moniker implementor deriving from CComMoniker must provide the CSLID of the moniker as the single template parameter (used in the implementation of the GetClassID() member function of IPersist and the GetUnmarshalClass() member function of IMarshal). The implementor may override any of the base class's member functions but must implement these three IMoniker members:

STDMETHODIMP BindToObject( IBindCtx* pbc, IMoniker* pmkToLeft, REFIID riidResult, void** ppvResult);


        
            STDMETHODIMP GetDisplayName(
            

               IBindCtx* pbc,
            

               IMoniker* pmkToLeft,
            

               LPOLESTR* ppszDisplayName);
        
        
            STDMETHODIMP ParseDisplayName(
            

               IBindCtx* pbc,
            

               IMoniker* pmkToLeft,
            

               LPOLESTR pszDisplayName,
            

               ULONG* pchEaten,
            

               IMoniker** ppmkOut);

As a aid in parsing display names, the CComMoniker class provides the following helper function:

bool MatchesProgID( const wchar_t* pwszDisplayName, // Display name being parsed const wchar_t** ppwszDisplayParam); // Pointer to character past :
This function checks the display name for a leading ProgID or VersionIndependentProgID followed by a colon and returns a pointer to the first character of the display name parameter(s), i.e. one character past the colon. The implementation of this function requires the derived class to implement the following member functions:

virtual const wchar_t* ProgID() =0; virtual const wchar_t* VersionIndependentProgID() =0;


        
            e.g.
        
        
            const wchar_t* ProgID() { return L"dm.meow.1"; }
            

            const wchar_t* VersionIndependentProgID() { return L:dm.meow"; }

CoMeowMoniker Implementation

The MeowMoniker is an ATL object named CoMeowMoniker. It derives from CComMoniker and provides an implementation of the required members only. The bulk of the implementation is contained in the two member functions, MarshalInterface() and UnmarshalInterface(). These two member functions manage the Base64 encoding and decoding of the interface pointer. The actual Base64 implementation is kept in Base64.cpp.

CoFeline Implementation

The Feline is an ATL object named CoFeline. Its implementation of GetDisplayName() uses a MeowMoniker. Its implementation of ParseDisplayName() uses MkParseDisplayName() so that any moniker's display name can be used.

YACL

The implementation of the MeowMoniker is based on utilities provided in the YACL (Yet Another COM Library), developed and maintained by Don Box and available at Don's YACL web site. The pieces of YACL
that I have used, I've included in the appropriate directories.

Revisions

6/15/98

Updated MeowMoniker to perform GetSizeMax properly.
Updated MeowMoniker and CComMonikerBase to use CComPtr and CComQIPtr instead of SmartInterface.
Removed use of HRESULTEX and therefore the use of C++ exception handling.
Moved some includes around.
Reduced RelMinDepend build from 89KB to 80KB. Could probably reduce it more if I could find Matt Pietrek's tinycrt and stop using the real CRT.

Copyright

MeowMoniker, copyright (c) 1997, Chris Sells.
Feline, copyright (c) 1997, Chris Sells.
CComMoniker, copyright (c) 1997, Don Box, Tim Ewald and Chris Sells.
YACL, copyright (c) 1997, Don Box.
Extensions to YACL, copyright (c) 1997, Tim Ewald and Chris Sells.
All rights reserved. NO WARRANTIES ARE EXTENDED. USE AT YOUR OWN RISK.