# Generic Host Integration

All CliCommands provide integration with .NET's Generic Host functionality. Through this integration you get:

• A dependency injection (DI) framework
• A logging framework (via DI and ILogger<T>)
• A configuration system
• A lifetime of "hosted services" - that automatically starts and stops all registered server classes.

Side note: To better understand how IHostBuilder work, see Generic Host - demystified.

To interact with the Generic Host (via its IHostBuilder interface), you need to override one or both of the following methods in your CliCommand sub class:

• ConfigureServices
• ConfigureApplication

Like so:

class MyCliCommand : CliCommand
{
    protected override void ConfigureServices(HostBuilderContext context, IServiceCollection services)
    {
        // Register your services here; via "services.Add...()
        //services.AddSingleton<ITestService, TestService>();
    }

    protected override void ConfigureApplication(IHostBuilder hostBuilder)
    {
        // Add configuration sources, ...
    }
}

While the command is running, you get access to the DI system via the CliCommand.Services property.

Note: CliCommand.CreateHostBuilder() creates a host builder through the DefaultHostBuilderFactory class. This class creates a host builder with a reduced set of services (compared to Host.CreateDefaultBuilder()).

There's a CliCommand sub class called ServiceHostCliCommand: It's main purpose is to just run one or more servers (HTTP server, file server, ...).

This command runs indefinitely - until explicitly stopped (see below). It's (more or less) the equivalent of .NET's Generic Host wrapped in a CliCommand.

Each server must implemented IHostedService and then be registered via AddHostedService():

protected override void ConfigureServices(HostBuilderContext context, IServiceCollection services)
{
    service.AddHostedService<MyServer>();
}

Note: If you want to host an HTTP(S) server, it's recommended to use the AppMotor.HttpServer package. See its README for more details.

If you're running a ServiceHostCliCommand, you need to stop the command explicitly - or it will run forever.

There are various ways to stop a ServiceHostCliCommand. All of them will shutdown the application gracefully, i.e. by executing any existing shutdown code before terminating:

• You hit Ctrl+C.
• You can call ServiceHostCliCommand.Stop().
• You can obtain (via DI) the IHostApplicationLifetime instance and call StopApplication().
• You can pass a CancellationToken to the application's Run() method and then cancel it.

This ServiceHostCliCommand provides access to various events regarding the lifetime of the command via the IServiceHostLifetimeEvents interface.

public interface IServiceHostLifetimeEvents
{
    // Triggered when the ServiceHostCliCommand has fully started.
    public OneTimeEvent Started { get; }

    // Triggered when the ServiceHostCliCommand has completed a graceful shutdown.
    // The application will not exit until all event handlers registered on this event have completed.
    public OneTimeEvent Stopped { get; }

    // This token is canceled just before the "Stopped" event is triggered.
    public CancellationToken CancellationToken { get; }
}

You get the instance of IServiceHostLifetimeEvents either via the ServiceHostCliCommand.LifetimeEvents property or via dependency injection.