A registry-free Out-Of-Process COM server that also demonstrates 32-64 bit communication
The sample is composed of
- a .NET 8.0 COM Out-Of-Process server (meant to be run in x64 but that could be changed easily in the project's build configuration)
- a native x86, x64 and ARM64 console client written in C++
- a simple VBScript client.
Everything is reg-free. All clients can call the .NET Server.
Reg-Free COM is here based on a Type Library .TLB file (server.tlb) present aside the server .exe and the client .exe (no TLB is embedded in this sample). Both .NET and C++ projects have a specific app.manifest file that declares that type library.
That type library is necessary for COM to marshal the IServer COM interface between the COM server and its clients. If the sample was using a well-known interface (for example IOleCommandTarget - I used this one a lot because it's pretty generic), then it would not be necessary as the tlb would already be known.
If the IServer COM interface was IUnknown-derived instead of IDispatch-derived, or/and if it was using non COM-Automation compatible types (BSTR, VARIANT, double, etc. are COM-compatible types), then we would need to use custom proxy and stubs. They are not needed here because we use IDispatch and restrict ourselves to COM-Automation types. It's much easier to do so. It happens magically because OleAut32.dll builds a proxy and a stub dynamically from the tlb.
All this works with VBScript as VBScript only uses the server's IDispatch implementation ("late-binding"), not the IServer one ("early-binding"). One can do the same with a native client (no requirement for TLB), but using IServer is easier from C/C++ (or other native languages for that matter).
Sadly, there's no tooling in Visual Studio C# projects to build .tlb files from .idl (there is only in Visual Studio C++ projects!), so the C# project references an extra GetWindowsSDKPaths.targets file (to gather various Windows SDK and Visual studio paths), plus some extra lines in the .csproj to do that automatically.
The native client needs the server.tlb to run. Its build is dependent on at least one .NET project successful build.