Implementing a Feature Flag-based Endpoint Filter

Modified March 17, 2025

Tim Deschryver

timdeschryver.dev

Feature Filter link

 FeatureFilter.cs content_paste
public abstract class FeatureFilter : IEndpointFilter
{
    protected abstract string FeatureFlag { get; }
 
    private readonly IFeatureManager _featureManager;
 
    protected FeatureFilter(IFeatureManager featureManager)
    {
        _featureManager = featureManager;
    }
 
    public async ValueTask<object?> InvokeAsync(EndpointFilterInvocationContext context, EndpointFilterDelegate next)
    {
        var isEnabled = await _featureManager.IsEnabledAsync(FeatureFlag);
        if (!isEnabled)
        {
            return TypedResults.NotFound();
        }
 
        return await next(context);
    }
}

Feature Filter Implementation link

 WeatherforecastFeatureFilter.cs content_paste
public class WeatherforecastFeatureFilter : FeatureFilter
{
    protected override string FeatureFlag => "WeatherforecastFeature";
 
    public WeatherforecastFeatureFilter(IFeatureManager featureManager) : base(featureManager)
    {
    }
}

Registering the Feature Endpoint Filter link

 Program.cs content_paste
var builder = WebApplication.CreateBuilder(args);
builder.Services
    .AddFeatureManagement(builder.Configuration.GetSection("FeatureFlags"));
 
var app = builder.Build();
 
app.MapGet("/weatherforecast", () =>
{
    var forecast = Enumerable.Range(1, 5).Select(index =>
        new WeatherForecast
        (
            DateTime.Now.AddDays(index),
            Random.Shared.Next(-20, 55),
            summaries[Random.Shared.Next(summaries.Length)]
        ))
        .ToArray();
 
    return TypedResults.Ok(forecast);
})
.AddEndpointFilter<WeatherforecastFeatureFilter>();
 
app.Run();

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