dSPACE COM tools
dSPACE COM tools
COM (Component Object Model) remains a critical part of the Windows ecosystem, enabling interoperability between software components. Despite its age, COM is still widely used in many applications and systems. However, with the advent of .NET 5 and later versions, Microsoft has discontinued several tools that were essential for working with COM, such as tlbexp.exe and RegAsm.exe. This has left developers without built-in support for generating or registering COM Type Libraries (TLBs) from .NET assemblies.
There is no support in .NET Core or .NET 5+ for generating a COM Type Library (TLB) from a .NET assembly.
https://docs.microsoft.com/en-us/dotnet/core/native-interop/expose-components-to-com
To address this gap, dscom provides a modern replacement for these tools. It offers a command-line interface (CLI) and libraries that allow developers to:
dscom aims to replicate the functionality of the discontinued Microsoft tools while introducing additional features to simplify COM-related workflows in .NET 5+ and .NET Framework projects. Whether you are working with legacy systems or building new applications that require COM interoperability, dscom provides the tools you need to bridge the gap.
The dSPACE.Runtime.InteropServices.BuildTasks library provides build tasks which can be used to automatically generate TLBs at compile time.
The command-line interface (CLI) tool dscom serves as a modern replacement for several legacy tools, including tlbexp.exe, OleView (for viewing Type Libraries), and RegAsm.exe. It is designed to simplify and enhance workflows related to COM (Component Object Model) interoperability in .NET applications.
dscom.exeConvert an Assembly to a Type Library
dscom allows you to generate a COM Type Library (TLB) from a .NET assembly. This is particularly useful for enabling COM interoperability with .NET assemblies in environments where a TLB is required.
Convert a Type Library to a YAML File
With dscom, you can inspect the contents of a Type Library by converting it into a human-readable YAML file. This feature is helpful for debugging, documentation, or understanding the structure of a TLB.
Register a Type Library
The tool provides functionality to register a Type Library with the system, making it available for use by COM clients.
Unregister a Type Library
If a Type Library is no longer needed, dscom can unregister it, removing its association with the system.
Embed a Type Library into an Existing Assembly
dscom supports embedding an existing Type Library into a specified assembly. This feature is useful for scenarios where you want to bundle the TLB with the assembly for easier distribution and deployment.
Register an Assembly (Equivalent to RegAsm.exe)
The tool can register a .NET assembly for use with COM clients, similar to the functionality provided by RegAsm.exe. This includes creating the necessary registry entries to expose the assembly's classes to COM.
Unregister an Assembly (Equivalent to RegAsm.exe)
If an assembly is no longer required for COM interoperability, dscom can unregister it, cleaning up the associated registry entries.
These features make dscom a versatile and powerful tool for developers working with COM in modern .NET environments, addressing the gaps left by the deprecation of older tools while introducing additional capabilities to streamline the development process.
The installation is quite simple. You can use dotnet tool to install the dscom binary if you want to create a 64Bit TLB.
dotnet tool install --global dscomHere you can find all available versions:
https://www.nuget.org/packages/dscom/
Alternatively you can download dscom.exe from the release page.
https://github.com/dspace-group/dscom/releases
Use dscom --help to get further information.
c:\> dscom --help
Description:
dSPACE COM tools
Usage:
dscom [command] [options]
Options:
--version Show version information
-?, -h, --help Show help and usage information
Commands:
tlbexport <Assembly> Export the assembly to the specified type library
tlbdump <TypeLibrary> Dump a type library
tlbregister <TypeLibrary> Register a type library
tlbunregister <TypeLibrary> Unregister a type library
tlbembed <SourceTypeLibrary> <TargetAssembly> Embeds a source type library into a target file
regasm <TargetAssembly> Register an assemblyExample to create a TLB from an assembly:
c:\> dscom tlbexport MyAssembly.dll --out C:\path\to\output\MyAssembly.tlbFor more information about the command line options to create a TLB, use dscom tlbexport --help.
Usage:
dotnet add package dSPACE.Runtime.InteropServicesdSPACE.Runtime.InteropServices supports the following methods and classes:
If you miss the TypeLibConverter class and the ConvertAssemblyToTypeLib method in .NET, then the dSPACE.Runtime.InteropServices might help you.
This method should behave compatible to the .NET Framework method.
public object? ConvertAssemblyToTypeLib(
Assembly assembly,
string tlbFilePath,
ITypeLibExporterNotifySink? notifySink)Example:
using dSPACE.Runtime.InteropServices;
// The assembly to convert
var assembly = typeof(Program).Assembly;
// Convert to assembly
var typeLibConverter = new TypeLibConverter();
var callback = new TypeLibConverterCallback();
var result = typeLibConverter.ConvertAssemblyToTypeLib(assembly, "MyTypeLib.tlb", callback);
// Get the name of the type library
var typeLib2 = result as System.Runtime.InteropServices.ComTypes.ITypeLib2;
if (typeLib2 != null)
{
typeLib2.GetDocumentation(-1, out string name, out _, out _, out _);
Console.WriteLine($"TypeLib name: {name}");
}
// The callback to load additional type libraries, if necessary
public class TypeLibConverterCallback : ITypeLibExporterNotifySink
{
public void ReportEvent(ExporterEventKind eventKind, int eventCode, string eventMsg)
{
Console.WriteLine($"{eventCode}: {eventMsg}");
}
public object? ResolveRef(System.Reflection.Assembly assembly)
{
// Returns additional type libraries
return null;
}
}.NET +6 introduced ability to embed type library into assemblies with the ComHostTypeLibrary property. However, using this is not fully compatible with the dscom build tools as it requires a type library to be already generated prior to the build. This class provides the implementation for embedding a type library into an assembly via Win32 API p/invoke calls.
The class and method are static, so you only need to create a settings to provide parameter for the source type library and the target assembly for where the type library will be embedded.
It is important to note that type libraries are not bit-agnostic and therefore, it will not make sense to embed them in an AnyCPU assemblies. For .NET 5.0 and greater, that is not an issue since the generated *.comhost.dll are tied to a specific bitness. For .NET 4.8, it is strongly recommended that the assembly be built with either x64 or x86 rather than AnyCPU.
public static bool EmbedTypeLib(
TypeLibEmbedderSettings settings
)Example:
using dSPACE.Runtime.InteropServices;
var settings = new TypeLibEmbedderSettings
{
SourceTlbPath = "C:\\path\\to\\type\\library.tlb",
TargetAssembly = "C:\\path\\to\\assembly.dll"
};
TypeLibEmbedder.EmbedTypeLib(settings);IMPORTANT: Embedding the type library will alter the assembly, which may cause issues with signing the assembly. Therefore, the scenario of signing the assembly with a certificate or a strong name is not tested. If it is required that the assembly be signed, it is recommended that a build script be used to ensure proper sequence of steps is executed.
IMPORTANT: In order to embed the type library into the built assembly, the process must unload the assembly. As dotnet restricts the usage of unloadable assemblies via AssemblyLoadContext to pure CLR assemblies, embedding TLBs into an assembly may only work, if none of the assemblies loaded via --asmpath may be a mixed mode C++/CLI assembly. In this case, please use to different calls to dscom.exe / dscom32.exe or the separate dscom build tasks. For more information refer to issue #292.
The dSPACE.Runtime.InteropServices.RegistrationServices provides a set of services for registering and unregistering managed assemblies for use from COM.
This method is equivalent to calling CoRegisterClassObject in COM.
You can register a .NET class so that other applications can connect to it (For example as INPROC_SERVER or as a LOCAL_SERVER).
A outproc demo application is available here: examples\outproc
Example:
using dSPACE.Runtime.InteropServices;
var registration = new RegistrationServices();
var cookie = registration.RegisterTypeForComClients(typeof(Server.Common.Greeter),
RegistrationClassContext.LocalServer,
RegistrationConnectionType.MultipleUse);
Console.WriteLine($"Press enter to stop the server");
Console.ReadLine();
registration.UnregisterTypeForComClients(cookie);Registers the classes in a managed assembly to enable creation from COM.
using dSPACE.Runtime.InteropServices;
var registration = new RegistrationServices();
// Register MyAssembly
registration.RegisterAssembly(typeof(MyAssembly), true);
// Unregister MyAssembly
registration.UnregisterAssembly(typeof(MyAssembly), true);The dSPACE.Runtime.InteropServices.BuildTasks assembly and NuGet package provide the ability to create type libraries for a certain assembly at compile time.
To create a type library at compile time, simply add a reference to the nuget package, e.g. by using the command line.
dotnet add package dSPACE.Runtime.InteropServices.BuildTasksThe result should be a line as follows in your .csproj file:
<PackageReference Include="dSPACE.Runtime.InteropServices.BuildTasks" Version="0.17.0" NoWarn="NU1701">
<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
<PrivateAssets>all</PrivateAssets>
</PackageReference>Note: The extra attribute NoWarn="NU1701" is only required, if neither .NET 4.8 nor .NET 8.0 are targeted, since dotnet pack will currently not create a .NETStandard 2.0 compliant NuGet Package.
The build tasks puts a warning to the build log, if the desired type library has not been created, even if the backend has reported a success.
This warning is issued with the warning code DSCOM001, which can be collected in the WarningsAsErrors array:
<WarningsAsErrors>$(WarningsAsErrors);DSCOM001</WarningsAsErrors>This way the build stops, if the type library is not exported.
The build task can be parameterized with the following properties:
| Name | Description |
|---|---|
| _DsComTlbExt | Extension of the resulting type library. <br/> Default Value: .tlb |
| DsComTypeLibraryUniqueId | Overwrite the library UUID <br/> Default Value: Empty Guid |
| DsComOverideLibraryName | Overwrite the IDL name of the library. <br/> Default Value: Empty string |
| DsComRegisterTypeLibrariesAfterBuild | Use regasm call after the build to register type library after the build <br/> Default value: false |
| DsComTlbExportAutoAddReferences | Add referenced assemblies automatically to type libraries <br/> Default value: true |
| DsComTlbExportIncludeReferencesWithoutHintPath | If a Reference assembly does not provide a HintPath Metadata, the item spec shall be task. <br/> Default value: false |
| DsComExportTypeLibraryTargetFile | Path to the resulting file. <br/> Default value: $(TargetDir)\$(TargetName)$(_DsComTlbExt) * |
| DsComExportTypeLibraryAssemblyFile | Path to the source assembly file. <br/> Default value: $(TargetPath) * |
| DsComTypeLibraryEmbedAfterBuild | Embeds the generated type library into the source assembly file. <br /> Default value: false |
The build task consumes the following items:
| Name | Description |
|---|---|
| DsComTlbExportTlbReferences | Referenced type library files. |
| DsComTlbExportReferencePaths | Directories containing type libraries to use for export. |
| DsComTlbExportAssemblyPaths | Assemblies to add for the export. |
| DsComTlbAliasNames | Names to use as aliases for types with aliases. |
The CLI based task consumes these additional properties:
| Name | Description |
|---|---|
| DsComToolVerbose | Enables verbose option. |
| DsComToolSilent | Enables silent option. |
The CLI based task consumes these additional items:
| Name | Description |
|---|---|
| DsComToolSilence | Enables silence option for the given warnings |
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<DsComTypeLibraryUniqueId>f74a0889-2959-4e7b-9a1b-f41c54f31d74</DsComTypeLibraryUniqueId>
</PropertyGroup>
<ItemGroup>
<DsComTlbExportTlbReferences Include="C:\Path\To\My.tlb" />
<DsComTlbExportAssemblyPaths Include="C:\Path\To\Assemblies\Dependency.dll" />
<DsComTlbExportReferencePaths Include="C:\Path\To\Additional\TypeLibraries\" />
</ItemGroup>
</Project>When using the build tasks to create an 32 bit version for your type libraries / projects: The tasks require the .NET runtime in their specific CPU architecture to be installed.
So, for building 32 bit TLBs, dscom32 will be executed, which requires .NET runtime in x86 flavor to be available.
dscom installed by dotnet tool install can only handle AnyCPU or 64Bit assemblies and can only generate a 64bit TLB.
Depending on whether you want to process 32bit or 64bit assemblies, you need to download different executables from the release page.
Warning!
If your assembly is an AnyCPU assembly, then an yourassemblyname.comhost.dll is created as a 64 bit dll.
Therefore after calling regserv32.exe a 64 bit dll is registred.
To prevent this it is recommended that the assembly is compiled as a 32 bit assembly and not as an AnyCPU assembly.
see: https://github.com/dotnet/runtime/issues/32493
Warning! In order to use 32 bit support with the build targets, the x86 version of .NET must be installed, as dscom requests the hostfxr.dll to be loaded.
Both assemblies are ComVisible=false but lot of .NET Framework types are ComVisible=true.
But this is not the case for .NET (.NET Core and .NET >= 5).
Unlike mscorelib (the good old .NET Framework), no tlb is shipped for .NET.
As example the System.Exception class:
In case of mscorelib the System.Exception class is ComVisible=true:
[Serializable]
[ClassInterface(ClassInterfaceType.None)]
[ComDefaultInterface(typeof(_Exception))]
[ComVisible(true)]
public class Exception : ISerializable, _ExceptionIn case of System.Private.CoreLib (.NET Core and .NET >=5), the Exception class is ComVisible=false
[Serializable]
[TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
public class Exception : ISerializable
{The _Exception class interface (default interface in this case) is not available in .NET (.NET Core and .NET >=5).
The magic is in TypeForwardedFromAttribute.
If you try to load an .NET Framework assembly inside a .NET (.NET Core and .NET >=5) application, the runtime will forward the original type to
a type defined in the System.Private.CoreLib assembly.
classextern forwarder System.Exception
{
.assemblyextern System.Private.CoreLib
}Therefore you should make sure that you do not use any types from the mscorelib typelib in your .NET Framework project if you plan to migrate to .NET 5+
mscorelib typelib (all types are VT_UNKNOWN)
TypeLibExporterFlags is not supportedITypeLibExporterNotifySink is not COM visibleTypeLibConverter is not COM visibleAutoDual is not supported
IEnumVARIANT (stdole)GUID (stdole)OLE_COLOR(stdole)UnmanagedType.CustomMarshalerAssemblyMetadataAttribute value ".NETFrameworkAssembly".NET 6 is no longer supported by this project. Please use .NET 8 or later for full compatibility and support. If you require .NET 6 support, consider using an older release of dscom, but note that new features and bug fixes will not be backported.
Latest .NET compatible version is 1.15.2.
| feature | dscom |
|---|---|
| assemblyFile | supported |
| codebase | supported |
| registered | not supported |
| asmpath | supported |
| nologo | not supported |
| regfile | not supported |
| silent | not supported |
| tlb | supported |
| unregister | supported |
| verbose | not supported |
| help | supported |
We would be happy if you would like to contribute to this project.
We use VSCode as IDE, but feel free to use your preferred IDE.
You need >= .NET 8.0 SDK and .NET Full Framework >= 4.8 SDK installed on your machine.
Before submitting a pull request, please note the following points:
Code Formatting
Ensure the code is properly formatted using dotnet format --verify-no-changes.
Unit Tests
Run all tests with dotnet test and make sure all tests pass successfully.
Use dotnet build before running the tests to ensure that the project is built correctly and the dscom.exe is available.
Writing Tests
We like to have unit tests 😊
Write your own tests for any new features or bug fixes.
Verifying the tlb generation
To generate a TLB with dscom is the most important feature of this project.
Compare the output of dscom with that of tlbexp.
Use scripts\test.assembly.bat to generate a TLB with both dscom and tlbexp, and compare the outputs.
This script will use src\dscom.test.assembly\dscom.test.assembly.csproj to generate a TLB with both tools.
The script will attempt to open VSCode to facilitate the file comparison.
Ensure tlbexp is installed on your machine.
If you have Visual Studio installed, find tlbexp.exe in the C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.8 Tools folder, or use the Developer Command Prompt for VS to run tlbexp.
If you have any questions, feel free to ask in the issues section.
Thank you for your contribution ❤️