TheDanielDoyle.HostFilters 2.0.1

A framework for executing code before your .NET Core / ASP.NET Core application runs.

Host filters will run before the IHost runs. It's useful for executing migrations or performing validation tasks before you allow the IHost to run.

Quick start

1. Implement IHostFilter in a class, or derive from the built-in HostFilter or AsyncHostFilter base classes.
2. Register all concrete types implementing IHostFilter in dependency injection.
3. Replace RunAsync() with RunWithFiltersAsync() in your Program.cs Main method.
4. Run the application and laugh like Dr. Evil.

Registering Host Filters

You can register host filters using the provided AddHostFilters() method, with its overloads, or use your own Dependency Injection container to match up IHostFilter and concrete types.

AddHostFilters is an extension available for IServiceProvider, with overloads to accomodate each need. See below.

public void ConfigureServices(IServiceCollection services)
{
    services.AddHostFilters();
    services.AddHostFilters(typeof(Program).Assembly);
    services.AddHostFilter<HappyEasterHostFilter>();
    services.AddHostFilter(typeof(HappyHanukkahHostFilter));
}

Running Host Filters at Host Startup

Below is a typical ASP.NET Core Program.cs file. You can see RunAsync() has been replaced with RunWithFiltersAsync().

That is all that is required to run the host filters.

public class Program
{
    public static async Task Main(string[] args)
    {
        //await CreateHostBuilder(args).Build().RunAsync();
        await CreateHostBuilder(args).Build().RunWithFiltersAsync();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}

Create a Host Filter Examples

Synchronous example using HostFilter base class

public class HoldTheBeerHostFilter : HostFilter
{
    protected override async Task Handle(IServiceProvider services)
    {
        ILogger logger = services.GetService<ILogger<HoldTheBeerHostFilter>>();
        logger.LogInformation("Hold my beer!");
    }
}

Asynchronous example using AsyncHostFilter base class

public class GetHeadlinesHostFilter : AsyncHostFilter
{
    protected override async Task Handle(IServiceProvider services, CancellationToken cancellationToken)
    {
        await new SuperAmazesauceOperationAsync().JustDoItAsync(cancellationToken);
    }
}

Direct Interface Implementation example

public class BeatItHostFilter : IHostFilter
{
    public async Task Handle(IServiceProvider services, CancellationToken cancellationToken)
    {
        await new JustBeatItAsync().GimmeAHeeeHeeeAsync(cancellationToken);
    }
}

Samples

See https://github.com/TheDanielDoyle/HostFilters/tree/develop/Samples for .NET Core or ASP.NET Core examples.