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.Net Wrapper Status

  • GNU/Linux wrapper
  • MacOS wrapper
  • Windows wrapper

Introduction

Try to build a .NetStandard2.0 native (for win-x64, linux-x64 and osx-x64) nuget multi package using dotnet/cli and the new .csproj format.

Build the Binary Packages

To build the .Net nuget packages, simply run:

cmake -S. -Bbuild -DBUILD_DOTNET=ON
cmake --build build --target dotnet_package -v

note: Since dotnet_package is in target all, you can also ommit the --target option.

Technical Notes

First you should take a look at my dotnet-native project to understand the layout.
Here I will only focus on the CMake/SWIG tips and tricks.

Build directory layout

Since .Net use a .csproj project file to orchestrate everything we need to generate them and have the following layout:

<CMAKE_BINARY_DIR>/dotnet
build/dotnet
├── CMakeSwig
│   ├── Bar
│   │   ├── Bar.cs
│   │   ├── csBar.cs
│   │   ├── csBarPINVOKE.cs
│   │   └── SWIGTYPE_p_int64_t.cs
│   ├── Foo
│   │   ├── csFoo.cs
│   │   ├── csFooPINVOKE.cs
│   │   ├── Foo.cs
│   │   └── SWIGTYPE_p_int64_t.cs
│   └── FooBar
│       ├── csFooBar.cs
│       ├── csFooBarPINVOKE.cs
│       ├── FooBar.cs
│       └── SWIGTYPE_p_int64_t.cs
├── Directory.Build.props
├── logo.png
├── Mizux.CMakeSwig
│   └── Mizux.CMakeSwig.csproj
└── Mizux.CMakeSwig.runtime.linux-x64
    └── Mizux.CMakeSwig.runtime.linux-x64.csproj

src: tree build/dotnet --prune -I "obj|bin"

Table of Content

Requirement

You'll need the ".Net Core SDK 3.1" to get the dotnet cli. i.e. We won't/can't rely on VS 2019 since we want a portable cross-platform dotnet/cli pipeline.

Directory Layout

note: While Microsoft use runtime-<rid>.Company.Project for native libraries naming, it is very difficult to get ownership on it, so you should prefer to useCompany.Project.runtime-<rid> instead since you can have ownership on Company.* prefix more easily.

Build Process

To Create a native dependent package we will split it in two parts:

  • A bunch of Mizux.CMakeSwig.runtime.{rid}.nupkg packages for each Runtime Identifier (RId) targeted.
  • A meta-package Mizux.CMakeSwig.nupkg depending on each runtime packages.

note: Microsoft.NetCore.App packages follow this layout.

We have two use case scenario:

  1. Locally, be able to build a Mizux.CMakeSwig package which only target the local OS Platform, i.e. building for only one Runtime Identifier (RID).
    note: This is usefull when the C++ build is a complex process for Windows, Linux and MacOS.
    i.e. You don't support cross-compilation for the native library.

  2. Be able to create a complete cross-platform (ed. platform as multiple rid) Mizux.CMakeSwig package.
    i.e. First you generate each native Nuget package (runtime.{rid}.Mizux.CMakeSwig.nupkg) on each native architecture, then copy paste these artifacts on one native machine to generate the meta-package Mizux.CMakeSwig.

Local Mizux.CMakeSwig Package

Let's start with scenario 1: Create a Local Mizux.CMakeSwig.nupkg package targeting one Runtime Identifier (RID).
We would like to build a Mizux.CMakeSwig.nupkg package which only depends on one Mizux.CMakeSwig.runtime.{rid}.nupkg in order to dev/test locally.

The pipeline for linux-x64 should be as follow:
note: The pipeline will be similar for osx-x64 and win-x64 architecture, don't hesitate to look at the CI log. Local Pipeline Legend

Building local Mizux.CMakeSwig.runtime Package

disclaimer: for simplicity, in this git repository, we suppose the g++ and swig process has been already performed.
Thus we have the C++ shared library Native.so and the swig generated C# wrapper Native.cs already available.
note: For a C++ CMake cross-platform project sample, take a look at Mizux/cmake-cpp.
note: For a C++/Swig CMake cross-platform project sample, take a look at Mizux/cmake-swig.

So first let's create the local Mizux.CMakeSwig.runtime.{rid}.nupkg nuget package.

Here some dev-note concerning this Mizux.CMakeSwig.runtime.{rid}.csproj.

  • AssemblyName must be Mizux.CMakeSwig.dll i.e. all {rid} projects must generate an assembly with the same name (i.e. no {rid} in the name) 
    <RuntimeIdentifier>{rid}</RuntimeIdentifier>
<AssemblyName>Mizux.CMakeSwig</AssemblyName>
<PackageId>Mizux.CMakeSwig.runtime.{rid}</PackageId>
  • Once you specify a RuntimeIdentifier then dotnet build or dotnet build -r {rid} will behave identically (save you from typing it).
    • note: not the case if you use RuntimeIdentifiers (notice the 's')
  • It is recommended to add the tag native to the nuget package tags 
    <PackageTags>native</PackageTags>
  • Specify the output target folder for having the assembly output in runtimes/{rid}/lib/{framework} in the nupkg 
    <BuildOutputTargetFolder>runtimes/$(RuntimeIdentifier)/lib</BuildOutputTargetFolder>
    note: Every files with an extension different from .dll will be filter out by nuget.
  • Add the native shared library to the nuget package in the repository runtimes/{rib}/native. e.g. for linux-x64: 
    <Content Include="*.so">
  <PackagePath>runtimes/linux-x64/native/%(Filename)%(Extension)</PackagePath>
  <Pack>true</Pack>
  <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
</Content>
  • Generate the runtime package to a defined directory (i.e. so later in meta CMakeSwig package we will be able to locate it) 
    <PackageOutputPath>{...}/packages</PackageOutputPath>
  • Generate the Reference Assembly (but don't include it to this runtime nupkg !, see below for explanation) using: 
    <ProduceReferenceAssembly>true</ProduceReferenceAssembly>

Then you can generate the package using:

dotnet pack src/runtime.{rid}.CMakeSwig

note: this will automatically trigger the dotnet build.

If everything good the package (located where your PackageOutputPath was defined) should have this layout:

{...}/packages/Mizux.CMakeSwig.runtime.{rid}.nupkg:
\- Mizux.CMakeSwig.runtime.{rid}.nuspec
\- runtimes
   \- {rid}
      \- lib
         \- {framework}
            \- Mizux.CMakeSwig.dll
      \- native
         \- *.so / *.dylib / *.dll
...

note: {rid} could be linux-x64 and {framework} could be netstandard2.0

tips: since nuget package are zip archive you can use unzip -l <package>.nupkg to study their layout.

Building local Mizux.CMakeSwig Package

So now, let's create the local Mizux.CMakeSwig.nupkg nuget package which will depend on our previous runtime package.

Here some dev-note concerning this CMakeSwig.csproj.

  • This package is a meta-package so we don't want to ship an empty assembly file: 
    <IncludeBuildOutput>false</IncludeBuildOutput>
  • Add the previous package directory: 
    <RestoreSources>{...}/packages;$(RestoreSources)</RestoreSources>
  • Add dependency (i.e. PackageReference) on each runtime package(s) availabe: 
    <ItemGroup Condition="Exists('{...}/packages/Mizux.CMakeSwig.runtime.linux-x64.1.0.0.nupkg')">
  <PackageReference Include="Mizux.CMakeSwig.runtime.linux-x64" Version="1.0.0" />
</ItemGroup>
    Thanks to the RestoreSource we can work locally we our just builded package without the need to upload it on nuget.org.
  • To expose the .Net Surface API the CMakeSwig.csproj must contains a least one Reference Assembly of the previously rumtime package. 
    <Content Include="../Mizux.CMakeSwig.runtime.{rid}/bin/$(Configuration)/$(TargetFramework)/{rid}/ref/*.dll">
  <PackagePath>ref/$(TargetFramework)/%(Filename)%(Extension)</PackagePath>
  <Pack>true</Pack>
  <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
</Content>

Then you can generate the package using:

dotnet pack src/.CMakeSwig

If everything good the package (located where your PackageOutputPath was defined) should have this layout:

{...}/packages/Mizux.CMakeSwig.nupkg:
\- Mizux.CMakeSwig.nuspec
\- ref
   \- {framework}
      \- Mizux.CMakeSwig.dll
...

note: {framework} could be netstandard2.0

Testing local Mizux.CMakeSwig Package

We can test everything is working by using the CMakeSwigApp project.

First you can build it using:

dotnet build src/CMakeSwigApp

note: Since CMakeSwigApp PackageReference CMakeSwig and add {...}/packages to the RestoreSource. During the build of CMakeSwigApp you can see that Mizux.CMakeSwig and Mizux.CMakeSwig.runtime.{rid} are automatically installed in the nuget cache.

Then you can run it using:

dotnet build src/CMakeSwigApp

You should see something like this

[1] Enter CMakeSwigApp
[2] Enter CMakeSwig
[3] Enter CMakeSwig.{rid}
[3] Exit CMakeSwig.{rid}
[2] Exit CMakeSwig
[1] Exit CMakeSwigApp

Complete Mizux.CMakeSwig Package

Let's start with scenario 2: Create a Complete Mizux.CMakeSwig.nupkg package targeting multiple Runtime Identifier (RID).
We would like to build a Mizux.CMakeSwig.nupkg package which depends on several Mizux.CMakeSwig.runtime.{rid}.nupkg.

The pipeline should be as follow:
note: This pipeline should be run on any architecture, provided you have generated the three architecture dependent Mizux.CMakeSwig.runtime.{rid}.nupkg nuget packages. Full Pipeline Legend

Building All runtime Mizux.CMakeSwig Package

Like in the previous scenario, on each targeted OS Platform you can build the coresponding runtime.{rid}.Mizux.CMakeSwig.nupkg package.

Simply run on each platform

dotnet build src/runtime.{rid}.CMakeSwig
dotnet pack src/runtime.{rid}.CMakeSwig

note: replace {rid} by the Runtime Identifier associated to the current OS platform.

Then on one machine used, you copy all other packages in the {...}/packages so when building CMakeSwig.csproj we can have access to all package...

Building Complete Mizux.CMakeSwig Package

This is the same step than in the previous scenario, since we "see" all runtime packages in {...}/packages, the project will depends on each of them.

Once copied all runtime package locally, simply run:

dotnet build src/CMakeSwig
dotnet pack src/CMakeSwig

Testing Complete Mizux.CMakeSwig Package

We can test everything is working by using the CMakeSwigApp project.

First you can build it using:

dotnet build src/CMakeSwigApp

note: Since CMakeSwigApp PackageReference CMakeSwig and add {...}/packages to the RestoreSource. During the build of CMakeSwigApp you can see that Mizux.CMakeSwig and runtime.{rid}.Mizux.CMakeSwig are automatically installed in the nuget cache.

Then you can run it using:

dotnet run --project src/CMakeSwigApp

You should see something like this

[1] Enter CMakeSwigApp
[2] Enter CMakeSwig
[3] Enter CMakeSwig.{rid}
[3] Exit CMakeSwig.{rid}
[2] Exit CMakeSwig
[1] Exit CMakeSwigApp

Ressources

Few links on the subject...

Documention

First take a look at my dotnet-native project.

Related Issues

Some issue related to this process

Runtime IDentifier (RID)

Reference on .csproj format