I'm trying to marshal an interface to another thread.
Windows provides the convenient CoMarshalInterThreadInterfaceInStream helper function to take care of the boilerplate code associated with using CoMarshalInterface directly.
const Guid CLSID_Widget = "{F8383852-FCD3-11d1-A6B9-006097DF5BD4}";
const Guid IID_IWidget = "{EBBC7C04-315E-11D2-B62F-006097DF5BD4}";
//Create our widget
HRESULT hr = CoCreateInstance(CLSID_Widget, null,
CLSCTX_INPROC_SERVER | CLSCTX_LOCAL_SERVER,
IID_IWidget, out widget);
OleCheck(hr);
//Marshall the interface into an IStream
IStream stm;
hr = CoMarshalInterThreadInterfaceInStream(IID_IWidget, widget, out stm);
OleCheck(hr);
Except that the call to CoMarshalThreadInterfaceInStream fails with:
REGDB_E_IIDNOTREG (0x80040155)
Interface not registered
Go directly to CoMarshalInterface
The COM API function CoMarshalInterThreadInterfaceInStream provides a simple wrapper around CreateStreamOnHGlobal and CoMarshalInterface, as shown here:
// from OLE32.DLL (approx.)
HRESULT CoMarsha1InterThreadInterfaceInStream(
REFIID riid, IUnknown *pItf, IStream **ppStm)
{
HRESULT hr = CreateStreamOnHGlobal(0, TRUE, ppStm);
if (SUCCEEDED(hr))
hr = CoMarshalInterface(*ppStm, riid, pItf,
MSHCTX_INPROC, 0, MSHLFLAGS_NORMAL);
return hr;
}
So we can try ourselves.
IStream stm = new Stream()
hr = CoMarshallInterface(stm, IID_IWidget, widget,
MSHCTX_INPROC, // destination context is in-process/same host
NULL, // reserved, must be null
MSHLFLAGS_NORMAL // marshal once, unmarshal once
);
OleCheck(hr);
But that fails with:
REGDB_E_IIDNOTREG (0x80040155)
Interface not registered
Use standard marshaling
My class does not implement IMarhsal interface. This is right and normal.
By default, when CoMarshalInterface is first called on an object, the object is asked whether it wishes to handle its own cross-apartment communications. This question comes in the form of a QueryInterface request for the IMarshal interface. Most objects do not implement the IMarshal interface and fail this
QueryInterface request, indicating that they are perfectly happy to let COM
handle all communications via ORPC calls. Objects that do implement the
IMarshal interface are indicating that ORPC is inappropriate and that the object implementor would prefer to handle all cross-apartment communications
via a custom proxy. When an object implements the IMarshalinterface all references to the object will be custom marshaled.
When an object does not implement the IMarshal interface, all references to the object will be standard marshaled. Most objects elect to use standard marshaling.
So the the question becomes why is the standard COM marshaler having so much problems? What is the source of the error Interface not registered?
The interface is, in fact, not registered
The requires for COM are undocumented, but i can tell you that my interface GUID does not exist in:
HKEY_CLASSES_ROOT\Interface\{EBBC7C04-315E-11D2-B62F-006097DF5BD4}
The reason for this will be explained at the end.
I know that Windows provides you the CoRegisterPSClsid function that allows you to register an interface inside your process, so that the standard marshaler will be able to marshal it:
Enables a downloaded DLL to register its custom interfaces within its running process so that the marshaling code will be able to marshal those interfaces.
HRESULT CoRegisterPSClsid(
_In_ REFIID riid,
_In_ REFCLSID rclsid
);
Parameters:
riid [in]: A pointer to the IID of the interface to be registered.
rclsid [in]: A pointer to the CLSID of the DLL that contains the proxy/stub code for the custom interface specified by riid.
Which i can try calling, but what clsid do i use?
CoRegisterPSClsid(IID_IWidget, ???);
What is the CLSID of the DLL that contains the proxy/stub code for the custom interface specified by riid? Do i use my class itself?
CoRegisterPSClsid(IID_IWidget, CLSID_Widget);
That doesn't sound right; but i don't understand the COM standard marshaler well enough. Doesn't that CLSID have to be one of the standard COM marsharling classes; implementing IPSFactoryBuffer?
Either way, it doesn't work. I still get the error "Interface not registered".
Register the interface
I of course can register my interface in the registry:
HKEY_CURRENT_USER\Software\Classes\Interface\{EBBC7C04-315E-11D2-B62F-006097DF5BD4}
(default) = "IWidget"
But that doesn't fix it. Spelunking through the Interface registry keys, i notice that many specify a ProxyStubClsid32 entry.
When a new interface is requested on an object, the proxy and stub managers
must resolve the requested IID onto the CLSID of the interface marshaler.
Under Windows NT 5.0, the class store maintains these mappings in the NT
directory, and they are cached at each host machine in the local registry. The
machine-wide IID-to-CLSID mappings are cached at
HKEY_CLASSES_ROOT\Interface
and the per-user mappings are cached at
HKEY_CURRENT_USER\Software\Classes\Interface
One or both of these keys will contain a subkey for each known interface. If the interface has an interface marshaler installed, there will be an additional
subkey (ProxyStubClsid32) that indicates the CLSID of the interface
marshaler.
Except what class implements marshaling? I don't have a marshaler.
Can COM automatically marshal based on a TypeLibrary
Is it possible that if i register a Type Library with my Interface, that COM's standard marshaler will be able to bootstrap a proxy class on the fly?
I registered my interface above. Now i manually include the TypeLibrary:
HKEY_CURRENT_USER\Software\Classes\Interface\{EBBC7C04-315E-11D2-B62F-006097DF5BD4}\TypeLib
(default) = "{38D528BD-4948-4F28-8E5E-141A51090580}"
And if i monitor the registry during the call to CoMarshalInterface i see that it attempts, and does find, my Interface IID:
Operation: RegOpenKey
Path: HKCR\WOW6432Node\Interface\{EBBC7C04-315E-11D2-B62F-006097DF5BD4}
Result: SUCCESS
It then tries to look for a ProxyStubClsid32, and fails:
Operation: RegOpenKey
Path: HKCR\WOW6432Node\Interface\{668790E3-83CC-47E0-907F-A44BA9A99C8D}\ProxyStubClsid32
Result: NAME NOT FOUND
My hope would then be that the standard COM marshaler attempts to look for:
Operation: RegOpenKey
Path: HKCR\WOW6432Node\Interface\{668790E3-83CC-47E0-907F-A44BA9A99C8D}\TypeLib
But it doesn't.
The OLE Automation marshaler
According to Don Box, the Ole Automation marshaler (PSOAInterface - {00020424-0000-0000-C000-000000000046}) is able to build a stub/proxy out of a type library:
The Type Library Marshaler
When these specially annotated interfaces are encountered by RegisterTypeLib (or LoadTypeLib in legacy mode), COM adds ProxyStubClsid32 entries for the interface with the value {00020424-0000-0000-C0000-000000000046}. This GUID corresponds to the class PSOAInterface that is registered as living in OLEAUT32.DLL, the OLE automation DLL. Because of the DLL that it lives in, this marshaler is sometimes called the [oleautomation] marshaler, although it is also called the type library marshaler or the universal marshaler. I'll refer to it as the type library marshaler, since it really has very little to do with IDispatch. (In fact, it is common to use the [oleautomation] attribute on interfaces that don't derive from IDispatch directly or indirectly.)
The class factory for the type library marshaler does something very tricky in its CreateProxy and CreateStub routines. Rather than return a statically compiled vtable (which is impossible given the fact that the requested interface didn't exist when OLEAUT32.DLL was built as part of the OS), the type library marshaler actually builds an /Oicf-style proxy and stub based on the type library for the interface. Because there is no efficient way to find the ITypeInfo for an arbitrary interface, the LIBID and version of the interface's type library must be stored under the:
HKCR\Interface\{XXX}\TypeLib
registry key.
I tried to set PSOAInterface as my interface's ProxyStub class:
Register standard COM class PSOAInterface as our proxy stub clsid
HKEY_CURRENT_USER\Software\Classes\Interface\{EBBC7C04-315E-11D2-B62F-006097DF5BD4}\ProxyStubClsid32
(default) = "{00020424-0000-0000-C0000-000000000046}"
Register our type library for our interface
HKEY_CURRENT_USER\Software\Classes\Interface\{EBBC7C04-315E-11D2-B62F-006097DF5BD4}\TypeLib
(default) = "{38D528BD-4948-4F28-8E5E-141A51090580}"
Version = "1.0"
The type library itself is already registered:
HKEY_CURRENT_USER\Software\TypeLib\{38D528BD-4948-4F28-8E5E-141A51090580}\1.0\0\win32
(default) = "D:\Junk\ComLibraryProxyTest\Win32\Project1.dll"
But it still fails.
it reads HKCR\Interface\[IID_IWidget]
it reads HKCR\Interface\[IID_IWidget]\ProxyStubClsid32
But it:
never reads: HKCR\Interface\[IID_IWidget]\TypeLib
So it fails to proxy the object.
Questions
Is it possible for the standard COM "Ole Automation" marshaler to build a proxy class out of a Type Library at runtime?
Is it possible for me to build a proxy class out of a Type Library at runtime?
Background
CoMarshalInterface takes an interface pointer on input and writes the
serialized representation of the pointer to a caller-provided byte stream. This byte stream can then be passed to another apartment, where the
CoUnmarshalInterface API function uses the byte stream to return an interface
pointer that is semantically equivalent to the original object yet can be
legally accessed in the apartment that executes the CoUnmarshalInterface
call. When calling CoMarshalInterface, the caller must indicate how far away
the importing apartment is expected to be. COM defines an enumeration for
expressing this distance:
enum MSHCTX {
MSHCTX_INPROC = 4, // in-process/same host
MSHCTX_LOCAL = 0, // out-of-process/same host
MSHCTX_NOSHAREDMEM = 1, //16/32 bit/same host
MSHCTX_DIFFERENTMACHINE = 2, // off-host
};
It is legal to specify a greater distance than required, but it is more efficient
to use the correct MSHCTX when possible. CoMarshalInterface also allows
the caller to specify the marshaling semantics using the following marshal flags:
enum MSHLFLAGS {
MSHLFLAGS_NORMAL, // marshal once, unmarshal once
MSHLFLAGS_TABLESTRONG, // marshal once, unmarshal many
MSHLFLAGS_TABLEWEAK, // marshal once, unmarshal many
MSHLFlAGS_NOPING = 4 // suppress dist. garbage collection
Normal marshaling (sometimes called call marshaling) indicates that the
marshaled object reference must be unmarshaled only once, and if additional
proxies are needed, additional calls to CoMarshalInterface are required. Table
marshaling indicates that the marshaled object reference may be unmarshaled
zero or more times without requiring additional calls to CoMarshalInterface.
I think that all COM object type libraries, when compiled by MIDL, can automatically create a proxy/stub factory. But in my case:
if the COM standard marshaler can't find a proxy/stub factory for an interface, it returns the error REGDB_E_IIDNOTREG.
It may be the case that i have to either:
use CreateProxyFromTypeInfo and CreateStubFromTypeInfo to create my own proxy
let the standard COM marshaler automatically create a proxy/stub if there's a typeinfo chunk associated with the interface GUID.
Bonus Reading
Old New Thing: What are the rules for CoMarshalInterThreadInterfaceInStream and CoGetInterfaceAndReleaseStream?
Old New Thing: Why do I get the error REGDB_E_IIDNOTREG when I call a method that returns an interface?
Old New Thing: Why do I get E_NOINTERFACE when creating an object that supports that interface?
Don Box - MSJ: Standard Marshalling in COM (archive)
Mysterious disappearing acts by samples from Microsoft SDKs
What CoMarshalInterface actually needs is IMarshal implementation (pointer) for the given interface, so that API could request the marshaling magic from it and, in particular, request IMarshal::GetUnmarshalClass in order to obtain information who is going to do the reverse magic afterwards:
This method is called indirectly, in a call to CoMarshalInterface, by whatever code in the server process is responsible for marshaling a pointer to an interface on an object. This marshaling code is usually a stub generated by COM for one of several interfaces that can marshal a pointer to an interface implemented on an entirely different object.
You don't have IMarshal implemented on your widget, so you are going to get it somewhere from.
As you started your question mentioning that you "want to marshal an interface to another thread" and the code comment says "Create our widget" there is a chance that you can utilize IMarhsal implementation of free threaded marshaler. The question does not provide information to tell whether it is possible and/or acceptable solution.
Back to the challenge of obtaining a marshaler, you are trying to work this around by utilizing a "standard" marshaler by "registering the interface":
why is the standard COM marshaler having so much problems
[...]
I of course can register my interface in the registry
Well, this is not how things actually work.
Interface registration is not just a registry key that "okay, this IID has its own key in the registry". The purpose of such registration is to point where to look for proxy/stub pair for this interface. Your manual creating of registry entries cannot help here if you don't have a proxy/stub DLL for the interface in question. If you had it, you would just regsvr32 it the usual way to create the registry keys.
So called standard marshaler, your next try, is not supposed to marshal any interface and your IWidget in particular. OLE supplies so called "PSOAInterface" marshaler, which is capable of supplying proxy/stub pairs for OLE Automation compatible interfaces. Just for them! The marshaler does not have so much problems, it actually has just one: your IWidget is unlikely to be compatible or you would not have the problem in first place.
If your IWidget was compatible, had an associated type library, where it was marked as [oleautomation], the type library registration process would have automatically created the registry keys referencing PSOAInterface and supplying ProxyStubClsid32. Then marshaling API would have picked PSOAInterface for your widget, it would have picked up the registered type library, load details of the interface, then provided standard proxy/stub pair for it and that's it. Standard marshaler works just within these contraints and not just for any interface pointed to.
That is, your options are:
implement IMarshal on the widget server
make IWidget OLE Automation compatible, with type library, so that type library registration process activates "standard marshaler" PSOAInterface for your interface
build, if possible and applicable, proxy/stub implementation for your interface automatically generated by MIDL complier (you can check standard ATL DLL project, created from Visual Studio template on how it can be done - it creates additional project with "PS" suffix, for a supplementary proxy/stub DLL)
implement separately IMarshal in a standalone DLL, and register it with the registry and your IWidget interface, so that marshaling API would pick it up when it attempts to marshal the interface pointer (I suppose it's the only option here if your IWidget is OLE incompatible and you have reasons to not alter the original implementation)
use free threaded marshaler in the widget server if its restrictions are acceptable
Oh wait, hold on - there is another weird one. If you don't want or cannot afford, or you are reluctant to change the COM server (widget, that is) but you can modify client side code as you like, you can create a thin wrapper that implements two interfaces IWidget (all methods forward calls to real server) and IMarshal on client side, and pass its IWidget to the CoMarshalInterThreadInterfaceInStream API. This will force COM to use your marshaling without altering the original server. You are on your own, of course, to do the actual marshaling afterwards. It is unlikely that it matches your actual need, and it is just an abstract note to the discussion (which mostly consists of attempts to do impossible without details on interface itself and available options on modification of server implementation).
TL;DR: Actual questions:
Is it possible for the standard COM "Ole Automation" marshaler to build a proxy class out of a Type Library at runtime?
Short answer: yes.
Is it possible for me to build a proxy class out of a Type Library at runtime?
Short answer: yes, with the type library marshaler and IPSFactoryBuffer. Or if you're willing to use the undocumented CreateProxyFromTypeInfo and CreateStubFromTypeInfo.
I wonder why you'd want to this.
This question is riddled with red herrings.
I'm trying to marshal an interface to another thread.
(...) the call to CoMarshalThreadInterfaceInStream fails with:
REGDB_E_IIDNOTREG (0x80040155)
Interface not registered
A useful error code, in this case.
Go directly to CoMarshalInterface
(...) that fails with:
REGDB_E_IIDNOTREG (0x80040155)
Interface not registered
It's not by switching API calls that do essentially the same thing that you could solve your issue.
Use standard marshaling
My class does not implement IMarhsal interface.
Can you confirm it doesn't implement INoMarshal, IStdMarshalInfo and IAgileObject either, just to be exhaustive?
The interface is, in fact, not registered
This was expected.
I know that Windows provides you the CoRegisterPSClsid
(...)
Which i can try calling, but what clsid do i use?
CoRegisterPSClsid(IID_IWidget, ???);
If you don't have a proxy/stub, why would you go through this?
But to answer this question, a standard marshalers' CLSID is usually the same GUID as the first IID found in an IDL file.
Register the interface
I of course can register my interface in the registry:
HKEY_CURRENT_USER\Software\Classes\Interface\{EBBC7C04-315E-11D2-B62F-006097DF5BD4}
(default) = "IWidget"
But that doesn't fix it. Spelunking through the Interface registry keys, i notice that many specify a ProxyStubClsid32 entry.
You should read the documentation, instead of relying on what other registry entries contain.
(...) I don't have a marshaler.
This should be the actual problem. If this object is yours, how do you intend to marshal it? Please see the bottom section of my answer.
Can COM automatically marshal based on a TypeLibrary
This is clearly rhetoric. Why would you think of a type library just now, instead of to begin with? The rest of your question corroborates.
Now i manually include the TypeLibrary:
HKEY_CURRENT_USER\Software\Classes\Interface\{EBBC7C04-315E-11D2-B62F-006097DF5BD4}\TypeLib
(default) = "{38D528BD-4948-4F28-8E5E-141A51090580}"
You mention this twice.
But it:
never reads: HKCR\Interface[IID_IWidget]\TypeLib
The type library marshaler has its own cache of interface->type library. To clear the cache, try recreating the registry entries, logging off and logging on, or ultimately, reboot.
The object may implement IProvideClassInfo, I don't know if the type library marshaler actually cares to QueryInterface for this to fetch a runtime ITypeInfo to work with.
These are the main types of marshalers:
Standard marshalers, which are usually compiled into a DLL from C/C++ source code generated by MIDL (which consists mainly of declarations on how to marshal types)
The type library marshaler, which can marshal types at runtime based on automation-compatible type information
The free-threaded marshaler aggregated with CoCreateFreeThreadedMarshaler, which avoids marshaling between threads within the same process
Custom marshalers, which do whatever the developer wants, most commonly to implement marshal-by-value, or a free-threaded marshaler back when CoCreateFreeThreadedMarshaler didn't exist
The standard marshalers generated by MIDL consist mainly of declarations on how to marshal types in and out, so the way they work is in the same vein as the type library marshaler. According to Don Box, the result is very similar.
However, the actual declarations are very different. The type library marshaler works on type information that is meant to work in VB6 and (excluding certain things, such as user-defined types) scripting languages (mainly VBScript and JScript) and is intended to be consumed by IDEs (e.g. VB6, VBA, Delphi, OleView) and interop code generators (e.g. VC++ #import, tlbimp.exe, Delphi's "Import Type Library", Lisp 1 2), etc.
I am using a program which makes it possible to customize dialogues via vbscript. Now, the form has an attribute which seems to be a vbDataObject (VarType returns 13).
How can I read the content and create a new vbDataObject to assign it to the attribute?
Don't know if this is exactly the answer, but it seems that vbDataObject's are indeed COM objects, but they just do not expose an IDispatch interface (so they're not true automation objects). As such, VBScript just isn't capable of accessing their content, since it needs an IDispatch interface for it. It just has an IUnknown interface which it doesn't know what to do with.
Passing them around should be possible, though, so if another true automation COM object can manipulate them for you (maybe there is such an object in the app designed to do this?), you could use that to make an object with the correct settings and pass that to the form.
Another option is to contact the authors of the app and ask them if they're willing to give this one object an IDispatch interface as well. Since they presumably went the length to put IDispatch interfaces on most of their objects, this omission might just be an oversight on their part.
Is there an established pattern on how to compare two COM-objects based on their value (aka private state), instead of their identity (aka pointer to IUnknown)?
Object equality is a heavy implementation detail, a detail that's well hidden in COM. COM is an interface based object model, the fact that an implementation is required of those interfaces is carefully hidden. It comes up in just a few places, CoCreateInstance() being the obvious one. Less obvious are the rules for IUnknown. Whose proper implementation requires that you'll get the same IUnknown interface pointer when you QI through any of the implemented interfaces. This provides object identity, not object equality.
There is no standard COM interface type that is commonly used to test object equality. You'll just have to make your own. A simple one with an IsEqualTo() method gets the job done. Or you could just add that method to your default interface.
It depends on definition of "private state". A COM object does not have to have one. If the objects implement IPersist* family of interfaces, esp. IPersistStreamInit, then you can save both into persistent stream or property bag, and then compare storages directly, such as byte-by-byte comparison of the streams.
i'm faced with implementing an IDispatch interface. There are four methods, and fortunately 3 of them are easy:
function TIEEventsSink.GetTypeInfoCount(...): HResult;
{
Result := E_NOTIMPL;
}
function TIEEventsSink.GetTypeInfo(...): HResult;
{
Result := E_NOTIMPL;
}
function TIEEventsSink.GetIDsOfNames(...): HResult;
{
Result := E_NOTIMPL;
}
It's the last method, Invoke that is difficult. Here i am faced with having to actually case the DispID, and call my appropriate method; unmarhsalling parameters from a variant array.
function Invoke(
dispIdMember: DISPID;
riid: REFIID;
lcid: LCID;
wFlags: WORD;
var pDispParams: DISPPARAMS;
var pVarResult: VARIANT;
var pExcepInfo: EXCEPINFO;
var puArgErr: DWORD
): HRESULT;
Not wanting to have to write all the tedious boilerplate code, that i'm sure will have bugs, i went googling - rather than doing any work.
i found this snippit on the MSDN Documentation of IDispatch.Invoke:
Generally, you should not implement Invoke directly.
Excellent! i didn't want to implement it anyway! Continuing reading:
Instead, use the dispatch interface to create functions CreateStdDispatch and DispInvoke. For details, refer to CreateStdDispatch, DispInvoke, Creating the IDispatch Interface and Exposing ActiveX Objects.
The Creating the IDispatch Interface link says:
You can implement IDispatch by any of the following means:
[snip]
Calling the CreateStdDispatch function. This approach is the simplest, but it does not provide for rich error handling or multiple national languages.
[snip]
Excellent, CreateStdDispatch it is:
Creates a standard implementation of the IDispatch interface through a single function call. This simplifies exposing objects through Automation.
HRESULT CreateStdDispatch(
IUnknown FAR* punkOuter,
void FAR* pvThis,
ITypeInfo FAR* ptinfo,
IUnknown FAR* FAR* ppunkStdDisp
);
i was going to call it as:
CreateStdDispatch(
myUnk, //Pointer to the object's IUnknown implementation.
anotherObject, //Pointer to the object to expose.
nil //Pointer to the type information that describes the exposed object (i has no type info)
dispInterface //the IUnknown of the object that implements IDispatch for me
);
What i cannot figure out is how the Windows API implemention of CreateStdDispatch knows what methods to call on my object - especially since CreateStdDispatch doesn't know what object-oriented language i'm using, or its calling conventions.
How will CreateStdDispatch know
what method to call for a given dispid?
the calling convention of my language?
how to handle exceptions from the language that my object oriented object is written in?
Note: i have no choice but to implement a dispinterface; i didn't define the interface. i wish it was a simple early bound IUnknown, but it tisn't.
Doesn't the ITypeInfo parameter passed into CreateStdDispatch expose all of the method information?
So you'd create type info first calling CreateDispTypeInfo and pass that through to CreateStdDispatch which can then use the type information to work out which method to call since CreateDispTypeInfo requires INTERFACEDATA which contains all this information
I could be way wrong since I don't have time to look into it but that would make sense to me.
I'll investigate this later and update the answer.
The short answer to your question is: neither CreateStdDispatch() nor the IDispatch implementation it creates knows anything at all about the methods to be called.
The object that you get back simply stores the parameters that you passed to CreateStdDispatch(), and for all IDispatch methods it only turns around and makes the corresponding calls on the ITypeInfo that you gave it. That is all.
If you pass nil for ptinfo as shown in your code then you only get E_INVALIDARG, since the implementing object cannot do anything at all without an ITypeInfo to which to delegate all the work.
If you inspect the code for CStdDisp in oleaut32.dll then you will find that it calls API functions like DispInvoke() (which also live in that DLL) instead of invoking the ITypeInfo methods directly, but these functions are all simple wrappers for calls to the ITypeInfo methods, without any further functionality.
In case anyone wonders: neither CreateStdDispatch() nor CStdDisp performs any additional magic; all they do is give you an IDispatch that does whatever the ITypeInfo that you passed in can do. Think of it as a kind of an adapter that allows you to plug an ITypeInfo into an IDispatch socket.
It is true that TAutoIntfObject.Create() needs a type library. However, all that the constructor does is call GetTypeInfoOfGuid() on it in order to get a type info pointer, to which the object then delegates most of the work related to dispatch things.
Borland in their wisdom made the member variable for the type info pointer private, which means that you really need to hand the constructor some type library or other that contains the interface in question, instead of simply writing another constructor or overriding some virtual function. On the other hand it shouldn't be too hard to load the type library via the registry or to dump parts of it to a TLB file. Inspecting a TLB with OleView gives you actual compilable IDL which is often also Borland-compilable RIDL.
CreateStdDispatch() does not know anything about exceptions either. The catching of exceptions thrown from COM methods and their conversion to HRESULT and/or IErrorInfo is compiler magic induced by Delphi's safecall keyword on the implementing method.
The same goes for the translation of HRESULTs to exceptions when calling COM methods specified as safecall in their interface declarations. The compiler simply inserts a call to #CheckAutoResult after every invocation of a safecall method; this function checks the HRESULT and throws EOleSysError if appropriate.
Simply switch the Delphi debugger to disassembly ('CPU view') to inspect all the magic that the compiler does for you!