Uno.Wasm.Bootstrap provides a simple way to package C# .NET code, and run it from a compatible browser environment.

It is a standalone .NET Web Assembly (WASM) sdk bootstrapper taking the form of a nuget package.

Installing it on a .NET 5 project or .NET Standard 2.0 library with an entry point allows to publish it as part of a WASM distribution folder, along with CSS, Javascript and content files.

This package only provides the bootstrapping features to run a .NET assembly and write to the javascript console, through Console.WriteLine.

This package is based on the excellent work from @praeclarum's OOui Wasm MSBuild task.

• Create a .NET 5 Console Application, and update it with the following basic definition:

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5</TargetFramework>
    <MonoRuntimeDebuggerEnabled Condition="'$(Configuration)'=='Debug'">true</MonoRuntimeDebuggerEnabled>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Uno.Wasm.Bootstrap" Version="2.0.0-dev.69" />
    <PackageReference Include="Uno.Wasm.Bootstrap.DevServer" Version="2.0.0-dev.69" PrivateAssets="all" />
 </ItemGroup>

</Project>

• Create a .NET Standard 2.0 library, and update it with the following basic definition:

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netstandard2.0</TargetFramework>
    <MonoRuntimeDebuggerEnabled Condition="'$(Configuration)'=='Debug'">true</MonoRuntimeDebuggerEnabled>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Uno.Wasm.Bootstrap" Version="2.0.0-dev.69" />
    <PackageReference Include="Uno.Wasm.Bootstrap.DevServer" Version="2.0.0-dev.69" PrivateAssets="all" />
 </ItemGroup>

</Project>

• Add a main entry point:

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("Hello from C#!");
    }
}

• In visual studio, press F5 or Debug, then Start debugging
• A browser window will appear with your application
• The output of the Console.WriteLine will appear in the javascript debugging console

See below the instructions on how to install the Windows Subsystem for Linux.

• Build the project, the WASM output will be located in bin\Debug\netstandard2.0\dist.
• Run the server.py, which will open an HTTP server on http://localhost:8000. On Windows, use Python tools or the excellent Linux Subsystem.
• The output of the Console.WriteLine will appear in the javascript debugging console

Previously, the suggested project structure was a .NET Standard 2.0 project using the non-web projects SDK. To enable debugging and easier deployment, the support for Microsoft.NET.Sdk.Web has been added.

To upgrade a project from 1.1 to 1.2:

• If you had a <DotNetCliToolReference /> line, remove it
• Add the <PackageReference Include="Uno.Wasm.Bootstrap.DevServer" Version="1.2.0-dev.1" PrivateAssets="all" /> item in the same item group as the other nuget packages.

To upgrade a project from 1.0 to 1.1:

• Change Microsoft.NET.Sdk to Microsoft.NET.Sdk.Web in the Sdk attribute of your project
• Add the <DotNetCliToolReference Include="Uno.Wasm.Bootstrap.Cli" Version="1.0.0-dev.1" /> item in the same item group as the other nuget packages.

The .NET tooling uses the ILLinker, and can be configured using a linker directives file.

The Bootstrapper searches for a file placed in an ItemGroup named LinkerDescriptor. See examples below.

<linker>
    <assembly fullname="Uno.Wasm.Sample"> <!-- Replace names to reflect your needs -->
        <namespace fullname="Uno.Wasm.Sample" />
    </assembly>

    <assembly fullname="WebAssembly.Bindings" />
</linker>

The documentation for this file can be found here.

It is also possible to provide the linker file as an embedded resource, which is useful when creating libraries. The linker step will discover those files and apply the configuration.

<!-- For application projects, include this in the .csproj file of your Wasm project -->
<ItemGroup>
    <LinkerDescriptor Include="LinkerConfig.xml" />
</ItemGroup>

<!-- For libraries, you should use this syntax instead -->
<ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
	<EmbeddedResource Include="LinkerConfig.xml">
		<LogicalName>$(AssemblyName).xml</LogicalName>
	</EmbeddedResource>
</ItemGroup>

The Linker can be disabled completely by setting the WasmShellILLinkerEnabled property to false. This property has no effect when building with AOT enabled.

The bootstrapper supports the feature switches configuration provided by .NET 5.

By default, some features are linked out as those are not likely to be used in a WebAssembly context:

• EventSourceSupport
• EnableUnsafeUTF7Encoding
• HttpActivityPropagationSupport

If you need to enable any of those features, you can set the following in your csproj first PropertyGroup:

<EventSourceSupport>true</EventSourceSupport>

The easiest way to publish the build results is to use the Visual Studio publish menu on your project. This will allow to use all the features provided by the standard experience, as described in the Deploy to Azure App Service.

The publication of the application must be done in .NET Framework hosting (and not .NET Core), as the app uses the web.config file for the server configuration, and to enable the use of pre-compression.

For deeper integration in the publishing pipeline, the WasmShellOutputPackagePath property is defined by the bootstrapper after the BuildDist target, which contains the path to the generated package_XXX content.

Using Windows 10, serving the app through a small Web Server is done through WSL.

Here's how to install it:

• Search for Ubuntu in the Windows Store: https://www.microsoft.com/en-us/search/result.aspx?q=ubuntu
• Install Ubuntu 18.04 or later, and follow the instructions during the first run
  • If you have another distribution installed make sure that the 18.04 is the default using wslconfig /s "Ubuntu-20.04". You can list your active distributions with wslconfig /l
  • Note that WSL 2 is considerably slower than WSL 1 for the boostrapper scenario. You will need to set your distribution to version 1 using wsl --set-version "Ubuntu-20.04" 1.
• Once you've built your project, you should see a path to the project dll
• In the Ubuntu shell, type cd `wslpath "[the_path_to_your_bin_folder]\dist"`
• Type python3 server.py
  • If this command does not exist, run the following sudo apt-get install python3
• Using your favorite browser, navigate to http://localhost:8000

Debugging is supported through the integration of a .NET Core CLI component, which acts as a static files server, as well as a debugger proxy for Chrome (other browsers are not supported).

In order to debug an Uno.Wasm.Boostrap enabled project, the Mono runtime debugger must be enabled:

<PropertyGroup Condition="'$(Configuration)'=='Debug'">
   <MonoRuntimeDebuggerEnabled>true</MonoRuntimeDebuggerEnabled>
</PropertyGroup>

Debug symbols need to be emitted and be of the type portable:

<PropertyGroup Condition="'$(Configuration)'=='Debug'">
    <DebugType>portable</DebugType>
    <DebugSymbols>true</DebugSymbols>
</PropertyGroup>

Finally, the DEBUG constant must be defined

<PropertyGroup Condition="'$(Configuration)'=='Debug'">
    <DefineConstants>$(DefineConstants);TRACE;DEBUG</DefineConstants>
</PropertyGroup>

Doing so will enable the deployment of pdb files to the browser, and allow for the mono debugger proxy to use them.

For the time being, you will also need to make sure that mscorlib is disabled in the Linker configuration file:

<!-- Required for debugging -->
<assembly fullname="mscorlib" />
<assembly fullname="System.Core" />

.NET for WebAssembly now has integrated preliminary support for in-browser debugging. Refer to this document for up-to-date information on how to set up the debugging.

Starting from Visual Studio 2019 16.6 Preview 1, it is possible to debug a WebAssembly app.

If you're updating from a previous version of the bootstrapper, make sure to manually update the Uno.Wasm.Bootstrap.Cli package to the same version as the Uno.Wasm.Bootstrap package in your csproj file.

To enable the debugging, add the following line to your launchSettings.json file:

"inspectUri": "{wsProtocol}://{url.hostname}:{url.port}/_framework/debug/ws-proxy?browser={browserInspectUri}"

in every profile section of the file, below each "launchBrowser": true, line.

Press F5 to start debugging.

Note that breakpoints in the main entry point of the executable are currently ignored.

The boostrapper also supports debugging directly in the browser debugging tools.

In Visual Studio:

• Make your project the startup project (right-click set as startup)
• In the debugging toolbar:
  • Select IIS Express as the debugging target
  • Select Chrome as the Web Browser
  • Make sure script debugging is disabled
• Start the debugging session using F5 (or Start Debug)
• Once your application has started, press Alt+Shift+D
• Follow the instructions on the web page
• You may need to refresh the original tab if you want to debug the entry point (Main) of your application.

The debugger is still under development, and here are a few things to look for:

• Breakpoints set sometimes disappear when the debugged page is reloaded
• If none of your assemblies appear in the debugger window, it's generally caused by the debugger caching previously loaded files. Make sure to hit Ctrl+Shit+R to force reload the debugged page.

The mono for WebAssembly runtime provides three execution modes, Interpreter, AOT and Mixed Mode Interpreter/AOT.

The execution mode can be set as follows:

<WasmShellMonoRuntimeExecutionMode>Interpreter</WasmShellMonoRuntimeExecutionMode>

The possible values are:

• Interpreter (the default mode)
• FullAOT
• InterpreterAndAOT

This modes is the slowest of all three, but allows for a large flexibility and debugging, as well as an efficient payload size.

The linker mode can also be completely disabled for troubleshooting, as this will not impact the wasm payload size.

This mode generates WebAssembly binary for all the referenced assemblies and provides the fastest code execution, but also generates the largest payload. This mode will not allow the execution of code that was not known at compile time (e.g. dynamically generated assemblies or loaded through Assembly.LoadFrom).

It is available on Windows 10 and Linux (18.04 and later, or similar).

Note that this mode and the mixed mode below are not available on windows 2019 hosted agents. Use Linux agents instead.

To ensure that AOT is only run under Linux, add the following to your project:

<WasmShellMonoRuntimeExecutionMode>FullAOT</WasmShellMonoRuntimeExecutionMode>

This mode allows for the AOT engine to selectively optimize methods to WebAssembly, and keep the rest as interpreted. This gives a very good balance when choosing between performance and payload size. It also has the advantage of reducing the build time, as less code needs to be compiled down to WebAssembly.

This feature is used in two passes:

• The first pass needs the creation of a profiled interpreter build, which records any methods invoked during the profiling session.
• The second pass rebuilds the application using the Mixed AOT/Interpreter mode augmented by the recording created during the first pass.

This mode gives very good results, where the RayTracer sample of this repository goes from an uncomressed size of 5.5MB to 2.9MB.

To create a profiled build:

• In your Wasm csproj, add the following:

<WasmShellGenerateAOTProfile>true</WasmShellGenerateAOTProfile>

• In your LinkerConfig.xml file, add the following:

<assembly fullname="WebAssembly.Bindings" />

• Run the application once, without the debugger (e.g. Ctrl+F5)
• Navigate throughout the application in high usage places.
• Once done, either:
  • Press the Alt+Shift+P key sequence
  • Launch App.saveProfile()
• Download the aot.profile file next to the csproj file
• Comment the WasmShellGenerateAOTProfile line
• Add the following lines:

<ItemGroup>
	<WasmShellEnableAotProfile Include="aot.profile" />
</ItemGroup>

• Make sure that Mixed mode is enabled:

<WasmShellMonoRuntimeExecutionMode>InterpreterAndAOT</WasmShellMonoRuntimeExecutionMode>

• Build you application again

Note that the AOT profile is a snapshot of the current set of assemblies and methods in your application. If that set changes significantly, you'll need to re-create the AOT profile to get optimal results.

The generated profile contains all the methods found to be executed during the profiling session, but some methods may still need to be manually excluded for some reasons (e.g. runtime or compile time errors).

The WasmShellAOTProfileExcludedMethods property specifies a semi-colon separated list of regular expressions to exclude methods from the profile:

<PropertyGroup>
    <WasmShellAOTProfileExcludedMethods>Class1\.Method1;Class2\.OtherMethod</WasmShellAOTProfileExcludedMethods>

    <!-- use this syntax to separate the list on multiple lines -->
    <WasmShellAOTProfileExcludedMethods>$(WasmShellAOTProfileExcludedMethods);Class3.*</WasmShellAOTProfileExcludedMethods>
</PropertyGroup>

The MixedModeExcludedAssembly is also used to filter the profile for assemblies, see below for more information.

Dumping the whole list of original and filtered list is possible by adding:

<PropertyGroup>
    <WasmShellGenerateAOTProfileDebugList>true</WasmShellGenerateAOTProfileDebugList>
</PropertyGroup>

This will generate files named AOTProfileDump.*.txt in the obj folder for inspection.

This modes allows for the WebAssembly generation of parts of the referenced assemblies, and falls back to the interpreter for code that was excluded or not known at build time.

This allows for a fine balance between payload size and execution performance.

At this time, it is only possible to exclude assemblies from being compiled to WebAssembly through the use of this item group:

<ItemGroup>
  <MonoRuntimeMixedModeExcludedAssembly Include="Newtonsoft.Json" />
</ItemGroup>

Adding assemblies to this list will exclude them from being compiled to WebAssembly.

When running with PG-AOT/FullAOT, exceptions generally do not provide stack traces, as WebAssembly as of the MVP does not yet support stack walking.

For the time being, it's still possible view browser stack traces in the log by enabling mono tracing.

First, you'll need to add the following class to your app:

static class MonoInternals
{
	[DllImport("__Native")]
	internal static extern void mono_trace_enable(int enable);
	[DllImport("__Native")]
	internal static extern int mono_trace_set_options(string options);
}

Then in the Main of your application, add the following:

MonoInternals.mono_trace_enable(1);
MonoInternals.mono_trace_set_options("E:all");

This will enable the tracing of all application exceptions (caught or not), along with the associated native host stack traces.

You can find the documentation for mono_trace_set_options parameter here.

• macOS 10.15 or later
• Homebrew
• .NET SDK 3.1 for netstandard2.0 builds or .NET SDK 5.0 for net5 builds
• A recent build of Mono MDK - Stable
• ninja: brew install ninja

We recommend that you install newer versions of Uno.Wasm.Bootstrap as it provides a better out-of-the-box experience(e.g. Emscripten is automatically installed).

Please note that AOT and Mixed Mode are not supported yet.

• Ubuntu 18.04+ or a container
• A stable build of mono
• A .NET SDK >= 3.1
• ninja: apt-get install ninja-build

We recommend that you install newer versions of Uno.Wasm.Bootstrap as it provides a better out-of-the-box experience(e.g. Emscripten is automatically installed).

The easiest is to build using the environment provided by the unoplatform/wasm-build docker image.

• A Windows 10 machine with WSL 1 or 2 with Ubuntu 18.04 installed.
• A stable build of mono
• A .NET SDK >= 3.1
• ninja: apt-get install ninja-build in WSL

If you have another distribution installed make sure that the 18.04 is the default using wslconfig /s "Ubuntu-20.04". You can list your active distributions with wslconfig /l Note that WSL 2 is considerably slower than WSL 1 for the boostrapper scenario. You will need to set your distribution to version 1 using wsl --set-version "Ubuntu-20.04" 1.

During the first use of WSL, if the environment is not properly setup, you will be guided to run the dotnet-setup.sh script that will install Mono, .NET Core and some additional dependencies.

The emscripten installation is automatically done as part of the build.

The boostrapper uses its own installation of emscripten, installed by default in $HOME/.uno/emsdk in the WSL filesystem. This can be globally overriden by setting the WASMSHELL_WSLEMSDK environment variable.

When building an application on Windows based CI servers, WSL is generally not enabled in base images. This can cause builds to fail if they require the use of static linking and/or AOT.

In order to work around this issue, the following property can be set:

<WasmShellForceDisableWSL>true</WasmShellForceDisableWSL>

It is important to note that generating a build this way, on a Windows CI server, without WSL enabled will generate an interpreter only build, and generate an invalid package if static linking was to be required.

When using GitHub actions:

<WasmShellForceDisableWSL Condition="'$(CI)'=='true'">true</WasmShellForceDisableWSL>

When using Azure Devops:

<WasmShellForceDisableWSL Condition="'$(BUILD_BUILDID)'=='true'">true</WasmShellForceDisableWSL>

The src/Uno.Wasm.Bootstrap.sln solution is a good way to build the bootstrapper itself, as well as sample solutions that validate the different features of the bootstrapper.

• Select a sample application, such as the Uno.Wasm.Sample project, and press Ctrl+F5 or run without debugger.
• The bootstrapper will be built as part of the process, and will generate a new webassembly site layout.
• Once the application has built, it will run in the selected browser in the Visual Studio debug location toolbar

Some tips:

• If you make modifications to the Uno.Wasm.Bootstrap, you may have to terminate all msbuild.exe processes, as they may lock files of that project.
• If you make modifications to the Uno.Wasm.Bootstrap.Cli project, you may have to terminate the dotnet.exe processes that link to your solution's subfolders, as they may lock files of that project.

Once the processes have been terminated, restart your build.

Debugging the bootstrapper task can be done by adding a Debugger.Launch() statement in the Run method of ShellTask.cs.

You can also make contributions through GitPod, and validate that your changes are appropriate.

Building and debugging samples is done through the command line.

1. Build a sample using :

   cd src/Uno.Wasm.Sample
   msbuild /r /bl
   

2. Start the web server to serve the sample on port 8000:

   cd bin/Debug/netstandard2.0/dist
   python3 server.py
   

3. The GitPod IDE will open a preview window with the content of the site. You may need to open the browser debugger window to see the results of the sample's execution.

Click on the button below to try this out!

Support for Emscripten's dynamic linking has been removed from the boostrapper as of version 1.1, as it has been too unstable to work with.

Instead, use Static Linking below.

Statically linking Emscripten LLVM Bitcode (.bc and .a files) files to mono is supported on both Windows 10 and Linux. To build on Windows please refer to the AOT environment setup instructions.

This linking type embeds the .bc or .a files with the rest of the WebAssembly modules, and uses normal webassembly function invocations that are faster than with dynamic linking.

Any .bc or .a file placed as content in the built project will be statically linked to the currently running application.

This allowing for p/invoke to be functional when resolving methods from the loaded module. If you have a .bc or a .a file you don't want to be include in the linking, you may add the UnoAotCompile="false" metadata that way:

<ItemGroup>
    <!-- Deactivate the discovery of a .bc or a .a file for static linking -->
    <Content Update="path\to\my\file.bc" UnoAotCompile="False" />
</ItemGroup>

As emscripten's ABI is not guaranteed to be compatible between versions, it may also be required to include multiple versions of the same LLVM binaries, compiled against different versions of LLVM. In order to enable this scenario, the Uno Bootstrapper supports adding .bc files by convention.

If the bitcode file to be added is named libTest.bc, the following structure can be used in your project:

• libTest.bc/2.0.6/libTest.bc
• libTest.bc/2.0.9/libTest.bc

In this case, based on the emscripten version used by the mono runtime, the bootstrapper will choose the closest matching version.

Static linking may also require some additional emscripten flags, for instance when using libpng. In such a case, add the following to your project:

<ItemGroup>
	<WasmShellExtraEmccFlags Include="-s USE_LIBPNG=1"/>
</ItemGroup>

For more information, see the Uno.Wasm.StaticLinking.Aot sample side module build script.

In order to invoke emscripten and mono native functions, the bootstrapper exposes the special library name __Native.

For instance, the following enables the mono internal tracing:

static class MonoInternals
{
	[DllImport("__Native")]
	internal static extern void mono_trace_enable(int enable);
}

Or use emscripten functions:

[DllImport("__Internal_emscripten")]
public static extern void emscripten_console_log(string str);

.NET 5/6 for WebAssembly does not support Threading (as of 2021-01-01), enabling this option will result in build errors (missing dotnet.worker.js file)

Mono now supports the ability to create threads, in browsers that support it (Chrome 79+, Edge 81+). Threads are backed by atomics and WebWorkers.

To enable the support, add the following configuration:

<MonoWasmRuntimeConfiguration>threads-release</MonoWasmRuntimeConfiguration>

Note that executing javascript in the context of a thread stays in the worked that is assigned to the thread, thus modifying the DOM from that context will do nothing.

To update the UI, execution will need to go back to the main thread, generally by using a mecanism similar to System.Threading.Timer which uses setTimeout so execute on the main thread.

The IIS compression support has too many knobs for the size of generated WebAssembly files, which makes the serving of static files inefficient.

The Bootstrapper tooling will generate two folders _compressed_gz and _compressed_br which contain compressed versions of the main files. A set IIS rewriting rules are used to redirect the queries to the requested pre-compressed files, with a preference for Brotli.

When building an application, place the following file in the wwwroot folder to automatically enable the use of pre-compressed files.

The parameters for the compression are as follows:

• WasmShellGenerateCompressedFiles which can be true or false. This property is ignored when building MonoRuntimeDebuggerEnabled is set to true.
• WasmShellCompressedExtension is an item group which specifies which files to compress. By default wasm, clr, js, css and `html files are pre-compressed. More files can be added as follows:

  <ItemGroup>
    <WasmShellCompressedExtension Include=".db"/>
  </ItemGroup>

• WasmShellBrotliCompressionQuality which controls the compression quality used to pre-compress the files. The default value is 7.

Note that the pre-compressed files are optional, and if the rewriting rules are removed or not used (because the site is served without IIS), the original files are available at their normal locations.

The bootstrapper supports having a project loaded as part of a node application. To do so:

• Create a Wasm bootstrapper project, named MyApp.Wasm
• Create a Node.js TypeScript project in Visual Studio, named MyApp.Runner
• In boostrapper project, add the following :

  <WasmShellDistPath>../MyApp.Runner/app</WasmShellDistPath>
  <WasmShellMode>node</WasmShellMode>

• In the app.ts, add the following:

  require("./app/mono");

Run the application and the main method of the MyApp.Wasm will be executed.

The parameters of the node command line are provided to the app's main method when running the app as follows:

node app param1 param2

An example of the node.js support is available in the Uno.Wasm.Node.Sample and Uno.Wasm.Node.Sample.Runner.njsproj projects.

Providing additional JS files is done through the inclusion of EmbeddedResource msbuild item files, in a project folder named WasmScripts. Files are processed as embedded resources to allow for libraries to provide javascript files.

Additional CSS files are supported through the inclusion of EmbeddedResource msbuild item files, in a project folder named WasmCSS.

Additional Content files are supported through the inclusion of Content files. The folder structure is preserved in the output dist folder. There is 3 deployment modes for content files:

• Package: files using UnoDeploy="Package" mode will be deployed in the dist\package_<hash> folder and the folder structure will be preserved. This is the default mode for most files (see exclusions below).
• Root: files using UnoDeploy="Root" mode will be deployed directly in the dist\ folder and the folder structure will be preserved.
• None: files using the UnoDeploy="None" mode will be ignored and won't be deployed.

Exclusions:

1. Files in the WasmScript folder will be set as UnoDeploy="None" by default (they are not treat as content)

2. Files in the wwwroot folder will be set as UnoDeploy="Root" by default

3. You can manually set the deploy mode in the .csproj in the following way:

   <ItemGroup>
       <!-- Manually set a file to be deployed as "root" mode -->
       <Content Include="Path\To\My\File.txt" UnoDeploy="Root" />
   
       <!-- Manually set a file to be deployed as "package" mode -- overriding the default "root" mode for wwwroot -->
       <Content Include="wwwroot\config.json" UnoDeploy="Package" />
   
       <!-- Manually set a file to be deployed as "none" mode (not deployed) -->
       <Content Include="wwwroot\output.log" UnoDeploy="None" />
   </ItemGroup>

Asset files: dist/package_XXXX/uno-assets.txt contains the package relative paths of the content files that were copied to the dist/package_XXXX folder. It can be used to identify which assets are packaged with the application at runtime and avoid costly probing operations. Important: Will only contain files deployed in UnoDeploy="Package" mode.

A few files extensions are excluded (UnoDeploy="None")by default such as *.a, *.bc. .html files are those named web.config will default to UnoDeploy="Root".

IMPORTANT INFORMATION ABOUT BROWSER CACHE: Browsers will often cache files based on their final url. When deploying a file in the UnoDeploy="Root" mode, beware the browser could cache the previous version. Files the the UnoDeploy="Package" mode won't have this problem since the path name contains a hash of their content. It important to take that into consideration when deciding to use the UnoDeploy="Root" mode.

A Progressive Web App manifest link definition can be added to the index.html file's head:

• Use the WasmPWAManifestFile property to set the file name
• Add a Web App Manifest file.
• Ensure the build action is Content for this file so it gets copied to the output folder. The UnoDeploy="Package" mode (which is the default) must be used. This file must not be put in the wwwroot folder.
• Create a set of icons using the App Image Generator

iOS's support for home screen icon is optionally set by searching for a 1024x1024 icon in the PWA manifest. Not providing this image will make iOS generate a scaled-down screenshot of the application.

You can validate your PWA in the chrome audits tab. If your PWA has all the appropriate metadata, the PWA installer will prompt to install your app.

By default, the msbuild task will calculate a hash for binary files in your project and will use the Subresource Integrity to validate that the right set of files are loaded at runtime.

You can deactivate this feature by setting this property in your .csproj file:

<WashShellUseFileIntegrity>False</WashShellUseFileIntegrity>

The WashShellGeneratePrefetchHeaders controls the generation of <link rel="prefetch" /> nodes in the index.html header.

It is enabled by default and allows for the browser to efficiently fetch the applications webassembly and .NET assemblies files, while the JavaScript and WebAssembly runtimes are being initialized.

This prefetching feature is particularly useful if the http server supports HTTP/2.0.

Mono provides the ability to configure some features at initialization, such as logging or GC.

To set those variables, add the following to your project file:

<ItemGroup>
  <WasmShellMonoEnvironment Include="MONO_GC_PARAMS" Value="soft-heap-limit=512m,nursery-size=64m,evacuation-threshold=66,major=marksweep" />
  <WasmShellMonoEnvironment Include="MONO_LOG_LEVEL" Value="debug" />
  <WasmShellMonoEnvironment Include="MONO_LOG_MASK" Value="gc" />
</ItemGroup>

These lines change the configuration of the GC and logging, to determine when a GC occurs. More options are available in the Environment Variables section of the mono documentation.

The bootstrapper provides a set of environment variables that reflect the configuration provided at build time:

• UNO_BOOTSTRAP_MONO_RUNTIME_MODE, which specifies the runtime mode configuration (see above for valid values)
• UNO_BOOTSTRAP_LINKER_ENABLED, which is set to True if the linker was enabled, otherwise False
• UNO_BOOTSTRAP_DEBUGGER_ENABLED, which is set to True if the debugging support was enabled, otherwise False
• UNO_BOOTSTRAP_MONO_RUNTIME_CONFIGURATION, which provides the mono runtime configuration, which can be can either be release or debug.
• UNO_BOOTSTRAP_MONO_PROFILED_AOT, which specifies if the package was built using a PG-AOT profile.
• UNO_BOOTSTRAP_APP_BASE, which specifies the location of the app content from the base. Useful to reach assets deployed using the UnoDeploy="Package" mode.

Those variables can be accessed through Environment.GetEnvironmentVariable.

The Uno Bootstrapper uses RequireJS for dependency management, allowing for dependencies to be resolved in a stable manner.

For instance, a script defined this way, placed in the WasmScripts folder:

define(() => {
    var txt = document.createTextNode("Loaded !");
    var parent = document.getElementById('uno-body');
    parent.insertBefore(txt, parent.lastChild);
});

will be executed appropriately.

Dependencies can also be declared this way:

define([], function() { return MyModule; });

If you're taking a dependency on an AMD enabled library, you'll need to publish the library as it would outside of the normal require flow.

As an example, to be able to use html2canvas:

• Add the html2canvas.js file as an EmbeddedResource in the WasmScripts folder
• Then create an additional file called myapp.js, also as an EmbeddedResource

  require([`${config.uno_app_base}/html2canvas`], c => window.html2canvas = c);
  

• You'll then be able to access window.html2canvas from C# using eval().

Emscripten modules initialization is performed in an asynchronous way and the Bootstrapper will ensure that a dependency that exposes a module will have finished its initialization for starting the Main method of the C# code.

The msbuild property WasmShellIndexHtmlPath can be used to specify the path of a project-specific index.html file.

This file should contain the following markers, for the runtime to initialize properly:

• $(ADDITIONAL_CSS)
• $(ADDITIONAL_HEAD)

Use the Templates/Index.html file as an example.

The default configuration for the bootstrapper is to show the Uno Platform logo. This can be changed, along with the background color and progress bar color by doing the following:

• Create an AppManifest.js file in the WasmScripts folder
• Set its build action to EmbeddedResource
• Add the following content:

var UnoAppManifest = {
    splashScreenImage: "https://microsoft.github.io/microsoft-ui-xaml/img/winui-logo.png",
    splashScreenColor: "#00f",
    accentColor: "#f00",
}

Once the app start, the content will be updated to show the custom logo. The logo must be of size 630x300 (or same ratio).

• The msbuild property MonoRuntimeDebuggerEnabled can be set to true to allow for mono to output additional debugging details, and have the debugger enabled (not supported yet by the mono tooling).
• The msbuild property RuntimeConfiguration allows for the selection of the debug runtime but is mainly used for debugging the runtime itself. The value can either be release or debug.

The msbuild properties MonoWasmSDKUri and MonoWasmAOTSDKUri (for netstandard2.0 projects), and NetCoreWasmSDKUri(fornet5` projects) allow the override of the default SDK paths. Paths can be local files or remote files.

To select a different sdk build:

• For netstandard2.0 projects:
  • Navigate to the Mono-wasm CI
  • Select a build
  • Click on the "default" configuration
  • On the left click Azure Artifacts
  • Copy the mono-wasm-xxxx.zip uri or local zip file path to the MonoWasmSDKUri property
  • Copy the wasm-release-Linux-xxx.zip uri or local zip file to the MonoWasmAOTSDKUri property
• For net5 projects:
  • Generate a build from the https://github.com/unoplatform/Uno.DotnetRuntime.WebAssembly project
  • Copy the dotnet-runtime-wasm-XX-XX-Release.zip uri or local zip file path to the NetCoreWasmSDKUri property

Note that override properties require a zip file as the source, not an uncompressed folder.

If you are overriding the contents of the uncompressed SDK folder, for debugging purposes, you will need to set the WasmShellDisableSDKCheckSumValidation property to true to avoid the bootstrapper to recreate the SDK folder.

The SDKs are installed under Path.GetTempPath() by default, you may change this by setting the following msbuild property(or environment variable): WasmShellMonoTempFolder.

For example, on Windows, setting WasmShellMonoTempFolder to C:\MonoWasmSDKs, the mono-wasm-e351637985e sdk would be installed under C:\MonoWasmSDKs\mono-wasm-e351637985e instead of C:\Users\xxx\AppData\Local\Temp\mono-wasm-e351637985e.

The bootstrapper comes with a default mono-wasm SDK (which can be overridden per project with the msbuild properties MonoWasmSDKUri and MonoWasmAOTSDKUri), specified in the Constants.cs file.

To update to a later mono-wasm SDK:

• Navigate to the Mono-wasm CI
• Copy the mono-wasm-xxxx.zip uri to the DefaultSdkUrl constant field
• Copy the wasm-release-Linux-xxx.zip uri to the DefaultAotSDKUrl constant field
• Open the mono-wasm-xxxx.zip and copy the Mono.WebAssembly.DebuggerProxy.dll and .pdb to the CustomDebuggerProxy folder folder.

The bootstrapper supports Windows 10 long paths by default, but there may be cases where the \\?\ path format may not be supported.

In such a case, setting the <WasmShellEnableLongPathSupport>false</WasmShellEnableLongPathSupport> in the project file can disable this feature.

Additional documentation on the support for long paths is available here.

The integration with WSL provides a way for using AOT, Mixed mode or external bitcode support using Windows 10.

This feature is active only if one of those condition is true:

• The WasmShellMonoRuntimeExecutionMode property is FullAOT or `InterpreterAndAOT
• There is a *.bc or *.a file in the Content item group
• The WasmShellForceUseWSL is set to true

Otherwise, the WSL integration is not used and the mono runtime present in the SDK is used as-is.

To enable the profiling of the WebAssembly code, set te following parameter:

<WasmShellEnableEmccProfiling>true</WasmShellEnableEmccProfiling>

This will ensure that the toolchain keeps the function names so that the browser shows meaningful information in the Performance tab.

Note that code executed through the interpreter will not appear explicitly in the performance charts, as it is executed through the interpreter. Only AOTed code will be visible.

To enable native memory troubleshooting, it is possible to use LLVM's sanitizer feature.

To enable it, add the following to your project file:

<ItemGroup>
	<WasmShellExtraEmccFlags Include="-fsanitize=address" />
</ItemGroup>

This will allow for malloc/free and other related memory access features to validate for possible issues, like this one:

================================================================= dotnet.js:2498:16
==42==ERROR: AddressSanitizer: attempting free on address which was not malloc()-ed: 0x03116d80 in thread T0 dotnet.js:2498:16
    #0 0x1657f6 in free+0x1657f6 (http://localhost:57998/dotnet.wasm+0x1657f6) dotnet.js:2498:16
    #1 0x12eb3a in monoeg_g_free+0x12eb3a (http://localhost:57998/dotnet.wasm+0x12eb3a) dotnet.js:2498:16
    #2 0x19936 in ves_pinvoke_method+0x19936 (http://localhost:57998/dotnet.wasm+0x19936) dotnet.js:2498:16
    #3 0xb8a5 in interp_exec_method+0xb8a5 (http://localhost:57998/dotnet.wasm+0xb8a5) dotnet.js:2498:16
    #4 0xa0bb in interp_runtime_invoke+0xa0bb (http://localhost:57998/dotnet.wasm+0xa0bb) dotnet.js:2498:16
    #5 0x52fcf in mono_jit_runtime_invoke+0x52fcf (http://localhost:57998/dotnet.wasm+0x52fcf) dotnet.js:2498:16
    #6 0xc6a6f in do_runtime_invoke+0xc6a6f (http://localhost:57998/dotnet.wasm+0xc6a6f) dotnet.js:2498:16
    #7 0xc711a in mono_runtime_try_invoke+0xc711a (http://localhost:57998/dotnet.wasm+0xc711a) dotnet.js:2498:16
    #8 0xc9234 in mono_runtime_invoke+0xc9234 (http://localhost:57998/dotnet.wasm+0xc9234) dotnet.js:2498:16
    #9 0x7967 in mono_wasm_invoke_method+0x7967 (http://localhost:57998/dotnet.wasm+0x7967) dotnet.js:2498:16
    #10 0x80002ffa in Module._mono_wasm_invoke_method http://localhost:57998/dotnet.js:12282:51 dotnet.js:2498:16
    #11 0x800002e9 in ccall http://localhost:57998/dotnet.js:745:18 dotnet.js:2498:16
    #12 0x800002f4 in cwrap/< http://localhost:57998/dotnet.js:756:12

Showing that mono is trying to free some memory pointer that was never returned by malloc.

Note that the runtime performance is severely degraded when enabling this feature.