Promact.FeatureFlagService.LaunchDarkly 1.0.0

FeatureFlagService

Generic feature flag service implementation for checking flag state via different providers (PostHog, LaunchDarkly, Unleash).

Usage

IFeatureFlagService lives in the Promact.FeatureFlag namespace (the core package).

using Promact.FeatureFlag;

private IFeatureFlagService _featureFlagService;

public async Task MyMethod()
{
    var isEnabled = await _featureFlagService.IsFeatureEnabledAsync("my-feature-flag");

    if (isEnabled)
    {
        // ...
    }
}

PostHog

Add nuget package

Promact.FeatureFlagService.PostHog

ASP.NET Core projects

Add below in Program.cs (or Startup.cs inside ConfigureServices)

services.AddPostHogFeatureFlagService(options =>
{
    options.ApiKey = configuration["PostHog:ApiKey"];
    options.Host = configuration["PostHog:Host"];
    options.ProjectId = int.Parse(configuration["PostHog:ProjectId"]);
});

Add relevant appsettings.json values

"PostHog": {
  "ApiKey": "",
  "Host": "",
  "ProjectId": 0
}

Inject IFeatureFlagService in class constructor from where you want to check flags

public MyClass(IFeatureFlagService featureFlagService)
{
...
}

LaunchDarkly

Add nuget package

Promact.FeatureFlagService.LaunchDarkly

ASP.NET Core projects

Add below in Program.cs (or Startup.cs inside ConfigureServices)

services.AddLaunchDarklyFeatureFlagService(options =>
{
    options.SdkKey = configuration["LaunchDarkly:SdkKey"];
    options.Environment = configuration["LaunchDarkly:Environment"];
});

Add relevant appsettings.json values

"LaunchDarkly": {
  "SdkKey": "",
  "Environment": ""
}

By default, the per-request LaunchDarkly user context (user key, email, subscription) is built from well-known claim types on the current HttpContext. If your app uses different claim types, supply your own factory:

services.AddLaunchDarklyFeatureFlagService(options =>
{
    options.SdkKey = configuration["LaunchDarkly:SdkKey"];
    options.Environment = configuration["LaunchDarkly:Environment"];
    options.UserContextFactory = provider =>
    {
        var httpContext = provider.GetRequiredService<IHttpContextAccessor>().HttpContext;
        return new LaunchDarklyUserContextDetails
        {
            UserKey = httpContext?.User.FindFirst("sub")?.Value ?? "anonymous",
            Email = httpContext?.User.FindFirst("email")?.Value ?? "",
            Subscription = httpContext?.User.FindFirst("subscription")?.Value ?? "Basic",
        };
    };
});

Set options.Offline = true in tests or local development to avoid contacting LaunchDarkly's servers -- every flag then evaluates to its default value.

Inject IFeatureFlagService in class constructor from where you want to check flags

public MyClass(IFeatureFlagService featureFlagService)
{
...
}

Unleash

Add nuget package

Promact.FeatureFlagService.Unleash

ASP.NET Core projects

Add below in Program.cs (or Startup.cs inside ConfigureServices)

services.AddUnleashFeatureFlagService(options =>
{
    options.AppName = configuration["Unleash:AppName"];
    options.Environment = configuration["Unleash:Environment"];
    options.UnleashApi = configuration["Unleash:APIUrl"];
    options.ApiToken = configuration["Unleash:ApiToken"];
});

Add relevant appsettings.json values

"Unleash": {
  "AppName": "",
  "Environment": "",
  "APIUrl": "",
  "ApiToken": ""
}

Inject IFeatureFlagService in class constructor from where you want to check flags

public MyClass(IFeatureFlagService featureFlagService)
{
...
}

Unleash also supports subscription-level flag checks, which aren't part of the shared IFeatureFlagService contract -- inject the concrete UnleashFeatureFlagService directly:

public MyClass(UnleashFeatureFlagService unleashFeatureFlagService)
{
...
}

var isEnabledForSubscription = await unleashFeatureFlagService.IsFeatureForSubscriptionEnabledAsync("my-feature-flag");

By default, the subscription context (user id, subscription level) is built from well-known claim types on the current HttpContext. Supply your own factory via options.SubscriptionContextFactory if your app uses different claim types.