Featureflip.Client 2.0.0

Featureflip C# SDK

C# SDK for Featureflip - evaluate feature flags locally with near-zero latency.

Installation

dotnet add package Featureflip.Client

Quick Start

using Featureflip.Client;

var client = FeatureflipClient.Get("your-sdk-key");

> **Lifetime:** The client is designed to be used as a singleton. Calling `FeatureflipClient.Get()` multiple times with the same SDK key returns handles sharing one underlying client — you cannot accidentally open duplicate streaming connections. For dependency injection, `AddFeatureflip` registers it as a singleton by default.

var enabled = client.BoolVariation("my-feature",
    new EvaluationContext { UserId = "user-123" }, false);

if (enabled)
{
    Console.WriteLine("Feature is enabled!");
}

client.Dispose();

Configuration

var client = FeatureflipClient.Get(
    "your-sdk-key",
    new FeatureFlagOptions
    {
        BaseUrl = "https://eval.featureflip.io",  // Evaluation API URL (default)
        Streaming = true,                          // SSE for real-time updates (default)
        PollInterval = TimeSpan.FromSeconds(30),   // Polling interval if streaming=false
        FlushInterval = TimeSpan.FromSeconds(30),  // Event flush interval
        FlushBatchSize = 100,                      // Events per batch
        InitTimeout = TimeSpan.FromSeconds(10),    // Max wait for initialization
        ConnectTimeout = TimeSpan.FromSeconds(5),  // HTTP connection timeout
        ReadTimeout = TimeSpan.FromSeconds(10),    // HTTP read timeout
        WaitForInitialization = false,             // Block constructor until ready
        StartOffline = false,                      // Continue even if init fails
    }
);

The SDK key can also be set via the FEATUREFLIP_SDK_KEY environment variable.

Evaluation

var context = new EvaluationContext { UserId = "123" };

// Boolean flag
bool enabled = client.BoolVariation("feature-key", context, false);

// String flag
string tier = client.StringVariation("pricing-tier", context, "free");

// Integer flag
int limit = client.IntVariation("rate-limit", context, 100);

// Double flag
double ratio = client.DoubleVariation("rollout-ratio", context, 0.5);

// JSON flag
var config = client.JsonVariation("ui-config", context, new UiConfig { Theme = "light" });

// Generic
var value = client.Variation("feature-key", context, defaultValue);

Detailed Evaluation

var detail = client.VariationDetail("feature-key",
    new EvaluationContext { UserId = "123" }, false);

Console.WriteLine(detail.Value);        // The evaluated value
Console.WriteLine(detail.Reason);       // RuleMatch, Fallthrough, FlagDisabled, etc.
Console.WriteLine(detail.RuleId);       // Rule ID if reason is RuleMatch
Console.WriteLine(detail.ErrorMessage); // Error details if reason is Error

Event Flushing

// Force flush pending events
client.Flush();

// Or async
await client.FlushAsync();

Dependency Injection

// In Startup.cs or Program.cs
services.AddFeatureflipClient("your-sdk-key");

// Inject via constructor
public class MyService
{
    private readonly IFeatureflipClient _client;

    public MyService(IFeatureflipClient client)
    {
        _client = client;
    }
}

Testing

The IFeatureflipClient interface makes mocking straightforward:

var mock = new Mock<IFeatureflipClient>();
mock.Setup(c => c.BoolVariation("my-feature", It.IsAny<EvaluationContext>(), false))
    .Returns(true);

Features

• Local evaluation - Near-zero latency after initialization
• Real-time updates - SSE streaming with automatic polling fallback
• Event tracking - Automatic batching and background flushing
• DI support - AddFeatureflipClient() extension method
• Interface-based - IFeatureflipClient for easy mocking
• Multi-target - Supports .NET 8.0 and .NET Standard 2.0

Requirements

• .NET 8.0+ or .NET Standard 2.0 compatible runtime

License

MIT