Support hosted services in WebAssemblyHost

[Copilot]

This PR adds support for hosted services (IHostedService) in WebAssemblyHost, enabling automatic startup and shutdown of background services in Blazor WebAssembly applications.

Description

Applications using WebAssemblyHost (e.g. Blazor WebAssembly clients) did not support hosted services out of the box. Services registered with AddHostedService were ignored when using WebAssemblyHostBuilder, unlike in applications built with WebApplicationBuilder or HostApplicationBuilder. This prevented libraries like OpenTelemetry from working properly in Blazor WebAssembly apps, as they rely on hosted services for initialization.

The implementation adds hosted service lifecycle management to WebAssemblyHost:

• Service Discovery: Automatically discovers IHostedService implementations from the DI container
• Startup Integration: Starts hosted services during RunAsyncCore() after component state restoration
• Cleanup Integration: Stops hosted services during DisposeAsync() with proper error handling
• HostedServiceExecutor: Encapsulates hosted service lifecycle logic in a dedicated executor class registered in DI, with integrated exception handling and logging using LoggerMessage source generator pattern
• Clean Architecture: WebAssemblyHost simply resolves the executor from DI and calls it at the appropriate times, maintaining clean separation of concerns

Usage

Developers can now register hosted services in Blazor WebAssembly apps:

var builder = WebAssemblyHostBuilder.CreateDefault(args);

// Register hosted services - they'll start automatically
builder.Services.AddSingleton<IHostedService, MyBackgroundService>();

var host = builder.Build();
await host.RunAsync(); // Hosted services start here

Implementation Details

• Added Microsoft.Extensions.Hosting.Abstractions reference to enable IHostedService support
• Created HostedServiceExecutor class in the WebAssembly project to encapsulate hosted service lifecycle management
• Registered HostedServiceExecutor as a singleton in DI in WebAssemblyHostBuilder.InitializeDefaultServices()
• HostedServiceExecutor accepts ILogger<HostedServiceExecutor> and handles all exception aggregation and logging internally
• Hosted services start after component state restoration (matching the timing suggested in the original issue)
• Error handling ensures host disposal doesn't fail if hosted services throw exceptions during shutdown
• Uses LoggerMessage source generator pattern for structured logging, following codebase conventions in WebAssemblyRenderer and WebAssemblyNavigationManager
• WebAssemblyHost resolves the executor from DI and coordinates its invocation at the right times
• Follows the same architectural pattern as the Hosting project for consistency across the codebase

Testing

Added comprehensive test coverage:

• Service startup during host run
• Service shutdown during host disposal
• Error handling for faulty services
• Integration with service registration patterns

All existing WebAssemblyHost functionality remains unchanged and all tests pass.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Support hosted services in WebAssemblyHost</issue_title>
<issue_description>### Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

Applications using WebAssemblyHost (e.g. Blazor WebAssembly clients) do not support hosted services out of the box. Services registered with AddHostedService are ignored when using WebAssemblyHostBuilder, unlike in applications built with WebApplicationBuilder or HostApplicationBuilder.

Describe the solution you'd like

WebAssemblyHost should support automatically running hosted services registered with AddHostedService.

Additional context

This feature request has already been rejected in #33537. However, we might want to reconsider the decision. For example, support for hosted services might be beneficial for Open Telemetry integration in Blazor Wasm apps.</issue_description>

<agent_instructions>Look at

aspnetcore/src/Hosting/Hosting/src/Internal/HostedServiceExecutor.cs

Line 10 in 063ba34

private readonly IEnumerable<IHostedService> _services;

and

aspnetcore/src/Hosting/Hosting/src/Internal/WebHost.cs

Line 30 in 063ba34

private HostedServiceExecutor? _hostedServiceExecutor;

We want WebAssemblyHost to start the services here https://github.com/dotnet/aspnetcore/blob/main/src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHost.cs#L139</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@pavelsavara We should measure the size/perf impact of adding it by default for WASM

Fixes #63637

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[Copilot]

Pull request overview

This PR adds hosted service (IHostedService) lifecycle management to WebAssemblyHost, enabling Blazor WebAssembly applications to use background services automatically. This addresses the limitation where services registered with AddHostedService were previously ignored in WebAssembly applications, and was specifically requested to support libraries like OpenTelemetry that rely on hosted services.

Key changes:

• Hosted services are automatically started during RunAsyncCore() after component state restoration
• Hosted services are stopped during DisposeAsync() with error aggregation and logging
• Added dependency on Microsoft.Extensions.Hosting.Abstractions to enable IHostedService support

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/Components/WebAssembly/WebAssembly/src/Microsoft.AspNetCore.Components.WebAssembly.csproj	Adds reference to Microsoft.Extensions.Hosting.Abstractions package
src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHost.cs	Implements hosted service lifecycle with start/stop methods and disposal integration
src/Components/WebAssembly/WebAssembly/test/Microsoft.AspNetCore.Components.WebAssembly.Tests.csproj	Adds reference to Microsoft.Extensions.Hosting.Abstractions for test project
src/Components/WebAssembly/WebAssembly/test/Hosting/WebAssemblyHostTest.cs	Adds comprehensive tests for hosted service startup, shutdown, and error handling scenarios

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[Copilot]

Consider using the LoggerMessage source generator pattern for structured logging. The codebase convention in WebAssemblyRenderer and WebAssemblyNavigationManager uses partial static Log classes with [LoggerMessage] attributes for better performance and consistency. Add a private static partial class Log with a LoggerMessage method for this error.

[javiercn]

@copilot do this

[Copilot]

Updated to use LoggerMessage source generator pattern with a private static partial Log class. Changes in commit d8752fb.

[Copilot]

[nitpick] The condition check uses is not null which is correct according to nullable reference type conventions. However, the HostedServiceExecutor in src/Hosting/Hosting/src/Internal/HostedServiceExecutor.cs:43 uses != null for the same pattern. Consider using is not null consistently for better code alignment with C# null pattern matching practices, which this codebase already follows (see line 84, 105).

[maraf]

Looks good to me 👍