[browser] Support WasmFilesToIncludeInFileSystem in WasmSdk #120970

maraf · 2025-10-22T13:27:51Z

Use WasmFilesToIncludeInFileSystem items to automatically load files to VFS when the application is starting.

The identity of WasmFilesToIncludeInFileSystem needs to be a relative path to files a file in wwwroot (either physical or linked). The optional TargetPath metadata allows to modify file location in VFS. If the metadata is omitted, a default location will resolved from relative file path in wwwroot.

Example:

Having a wwwroot/file.txt file
- <WasmFilesToIncludeInFileSystem Include="file.txt" /> will load the file to /file.txt
- <WasmFilesToIncludeInFileSystem Include="file.txt" TargetPath="/mydata/file.txt" /> will load the file to /mydata/file.txt
Having a wwwroot/subdir/file.txt file
- <WasmFilesToIncludeInFileSystem Include="subdir/file.txt" /> will load the file to /subdir/file.txt
- <WasmFilesToIncludeInFileSystem Include="subdir/file.txt" TargetPath="/mydata/file.txt" /> will load the file to /mydata/file.txt

Fixes #99223

src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonBuilderHelper.cs

…iles

VFS imports were incorrectly generated as "es module" imports, where as they should be treated as "general URL" imports

pavelsavara · 2025-10-27T12:50:53Z

src/mono/wasm/testassets/WasmBasicTestApp/App/WasmBasicTestApp.csproj

  </ItemGroup>
+
+  <ItemGroup>
+    <WasmFilesToIncludeInFileSystem Include="Vfs1.txt" TargetPath="/myfiles/Vfs1.txt" />


What would happen if there is reference to non-existent file ?

It would get ignored. I could make it fail the build

That may be better

Copilot

Pull Request Overview

This PR implements support for automatically loading files into the WebAssembly Virtual File System (VFS) using the WasmFilesToIncludeInFileSystem item in the WasmSdk. Files specified with this item are loaded into VFS at application startup, with support for custom target paths via TargetPath metadata.

Key Changes:

Added VFS resource support in boot JSON generation to handle files marked with vfs: trait
Updated bundler-friendly mode to correctly reference VFS assets with relative paths
Implemented target path resolution with fallback to file's wwwroot relative path

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
`src/tasks/WasmAppBuilder/WasmAppBuilder.cs`	Updated virtual path prefix to respect RuntimeAssetsLocation
`src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs`	Added VFS resource handling in boot config generation
`src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonBuilderHelper.cs`	Fixed VFS asset path generation for bundler-friendly mode
`src/mono/wasm/testassets/WasmBasicTestApp/App/wwwroot/subdir/subsubdir/Vfs3.txt`	Test file for nested VFS path without custom TargetPath
`src/mono/wasm/testassets/WasmBasicTestApp/App/wwwroot/subdir/Vfs2.txt`	Test file for VFS with custom TargetPath
`src/mono/wasm/testassets/WasmBasicTestApp/App/wwwroot/main.js`	Added test scenario entry point
`src/mono/wasm/testassets/WasmBasicTestApp/App/wwwroot/Vfs1.txt`	Test file for root-level VFS with custom TargetPath
`src/mono/wasm/testassets/WasmBasicTestApp/App/WasmBasicTestApp.csproj`	Added WasmFilesToIncludeInFileSystem declarations for testing
`src/mono/wasm/testassets/WasmBasicTestApp/App/FilesToIncludeInFileSystemTest.cs`	Test code to verify VFS file existence
`src/mono/wasm/testassets/JavascriptBundlers/rollup.config.mjs`	Updated rollup to handle .txt files
`src/mono/wasm/Wasm.Build.Tests/FilesToIncludeInFileSystemTests.cs`	Integration test for VFS functionality
`src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets`	MSBuild integration for WasmFilesToIncludeInFileSystem
`eng/testing/scenarios/BuildWasmAppsJobsList.txt`	Registered new test class for CI

Copilot · 2025-10-27T14:18:09Z

src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs

+                {
+                    Log.LogMessage(MessageImportance.Low, "Candidate '{0}' is defined as VFS resource '{1}'.", resource.ItemSpec, assetTraitValue);
+
+                    var targetPath = assetTraitValue.Substring("vfs:".Length);


Use string slice operator assetTraitValue[\"vfs:\".Length..] instead of Substring for better performance and modern C# style.

Suggested change

var targetPath = assetTraitValue.Substring("vfs:".Length);

var targetPath = assetTraitValue["vfs:".Length..];

Copilot · 2025-10-27T14:18:09Z

src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonBuilderHelper.cs

                {
                    string escaped = EscapeName(string.Concat(asset.name));
-                    imports.Add($"import * as {escaped} from \"./{asset.name}\";");
+                    imports.Add($"import {escaped} from \"./{asset.name}\";");


Removing the * as from the import statement changes the import from a namespace import to a default import. This breaks compatibility for modules that export a namespace rather than a default export. If VFS assets are expected to be modules with namespace exports, this change will cause runtime errors.

Suggested change

imports.Add($"import {escaped} from \"./{asset.name}\";");

imports.Add($"import * as {escaped} from \"./{asset.name}\";");

Copilot · 2025-10-27T14:18:09Z

...nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets


+    <ItemGroup>
+      <WasmFilesToIncludeInFileSystem Condition="'%(WasmFilesToIncludeInFileSystem.TargetPath)' == ''">
+        <TargetPath>%(WasmFilesToIncludeInFileSystem.Identity)</TargetPath>


The TargetPath should be prefixed with '/' to ensure it's an absolute path in the VFS. According to the PR description, files should be loaded to paths like '/file.txt' and '/subdir/file.txt', but this sets TargetPath to 'file.txt' or 'subdir/file.txt' without the leading slash.

Suggested change

<TargetPath>%(WasmFilesToIncludeInFileSystem.Identity)</TargetPath>

<TargetPath>/%(WasmFilesToIncludeInFileSystem.Identity)</TargetPath>

maraf added 3 commits October 22, 2025 15:26

Support WasmFilesToIncludeInFileSystem in WasmSdk

7b9e236

WBT

89a33e5

Fix merge

747d9ae

maraf added this to the 11.0.0 milestone Oct 22, 2025

maraf self-assigned this Oct 22, 2025

maraf added arch-wasm WebAssembly architecture area-Build-mono os-browser Browser variant of arch-wasm labels Oct 22, 2025

pavelsavara reviewed Oct 22, 2025

View reviewed changes

src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/BootJsonBuilderHelper.cs Show resolved Hide resolved

maraf added 2 commits October 22, 2025 18:00

Register the test class

261e367

Fix typo in class name

09d3586

This was referenced Oct 22, 2025

[browser] Wasm.Build.Tests timeout - Timed out after 10s waiting for 'WASM EXIT' #116697

Open

Unable to pull image from mcr.microsoft.com #117164

Open

[wasm/browser] Failed to connect to socket /run/dbus/system_bus_socket #120176

Open

maraf added 5 commits October 23, 2025 09:53

Apply VFS trait only when we have any WasmFilesToIncludeInFileSystem

d935c34

WasmAppBuilder copies VFS to _framework

a04cf3f

Configure rollup for JavascriptBundlers WBT to treat .txt as static f…

2cca4eb

…iles

Simplify

2145d20

Fix VFS imports in JavascriptBunlderFriendly mode

6d8cd3e

VFS imports were incorrectly generated as "es module" imports, where as they should be treated as "general URL" imports

maraf mentioned this pull request Oct 24, 2025

[browser] Use WebAssembly SDK for runtime tests #120330

Draft

26 tasks

Don't LoadFilesToVfs on JavascriptBunlderFriendly scenario for build

239fc96

build-analysis bot mentioned this pull request Oct 24, 2025

The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

Open

3 tasks

Remove inline data

6e4432b

pavelsavara reviewed Oct 27, 2025

View reviewed changes

maraf marked this pull request as ready for review October 27, 2025 14:16

maraf requested review from akoeplinger, ilonatommy and lewing as code owners October 27, 2025 14:16

Copilot AI review requested due to automatic review settings October 27, 2025 14:16

Copilot AI reviewed Oct 27, 2025

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	var targetPath = assetTraitValue.Substring("vfs:".Length);
	var targetPath = assetTraitValue["vfs:".Length..];

	imports.Add($"import {escaped} from \"./{asset.name}\";");
	imports.Add($"import * as {escaped} from \"./{asset.name}\";");

	<TargetPath>%(WasmFilesToIncludeInFileSystem.Identity)</TargetPath>
	<TargetPath>/%(WasmFilesToIncludeInFileSystem.Identity)</TargetPath>

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maraf commented Oct 22, 2025 •

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