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README.md
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<!-- markdownlint-disable MD033 -->
<!-- x-hide-in-docs-start -->
<!-- NuGet doesn't support most HTML tags. Disabling dark mode support until https://github.com/NuGet/NuGetGallery/issues/8644 is resolved. -->
## .NET SDK
<!-- x-hide-in-docs-end -->
[](https://github.com/open-feature/spec/releases/tag/v0.7.0)
[
 <!-- x-release-please-version -->
](https://github.com/open-feature/dotnet-sdk/releases/tag/v2.0.0) <!-- x-release-please-version -->
[](https://cloud-native.slack.com/archives/C0344AANLA1)
[](https://codecov.io/gh/open-feature/dotnet-sdk)
[](https://www.nuget.org/packages/OpenFeature)
[](https://www.bestpractices.dev/en/projects/6250)
<!-- x-hide-in-docs-start -->
[OpenFeature](https://openfeature.dev) is an open specification that provides a vendor-agnostic, community-driven API for feature flagging that works with your favorite feature flag management tool or in-house solution.
<!-- x-hide-in-docs-end -->
## 🚀 Quick start
### Requirements
- .NET 6+
- .NET Core 6+
- .NET Framework 4.6.2+
Note that the packages will aim to support all current .NET versions. Refer to the currently supported versions [.NET](https://dotnet.microsoft.com/download/dotnet) and [.NET Framework](https://dotnet.microsoft.com/download/dotnet-framework) excluding .NET Framework 3.5
### Install
Use the following to initialize your project:
```sh
dotnet new console
```
and install OpenFeature:
```sh
dotnet add package OpenFeature
```
### Usage
```csharp
public async Task Example()
{
// Register your feature flag provider
await Api.Instance.SetProviderAsync(new InMemoryProvider());
// Create a new client
FeatureClient client = Api.Instance.GetClient();
// Evaluate your feature flag
bool v2Enabled = await client.GetBooleanValueAsync("v2_enabled", false);
if ( v2Enabled )
{
//Do some work
}
}
```
## 🌟 Features
| Status | Features | Description |
| ------ | ----------------------- | ---------------------------------------------------------------------------------------------------------------------------------- |
| ✅ | [Providers](#providers) | Integrate with a commercial, open source, or in-house feature management tool. |
| ✅ | [Targeting](#targeting) | Contextually-aware flag evaluation using [evaluation context](https://openfeature.dev/docs/reference/concepts/evaluation-context). |
| ✅ | [Hooks](#hooks) | Add functionality to various stages of the flag evaluation life-cycle. |
| ✅ | [Logging](#logging) | Integrate with popular logging packages. |
| ✅ | [Domains](#domains) | Logically bind clients with providers. |
| ✅ | [Eventing](#eventing) | React to state changes in the provider or flag management system. |
| ✅ | [Shutdown](#shutdown) | Gracefully clean up a provider during application shutdown. |
| ✅ | [Extending](#extending) | Extend OpenFeature with custom providers and hooks. |
> Implemented: ✅ | In-progress: ⚠️ | Not implemented yet: ❌
### Providers
[Providers](https://openfeature.dev/docs/reference/concepts/provider) are an abstraction between a flag management system and the OpenFeature SDK.
Here is [a complete list of available providers](https://openfeature.dev/ecosystem?instant_search%5BrefinementList%5D%5Btype%5D%5B0%5D=Provider&instant_search%5BrefinementList%5D%5Btechnology%5D%5B0%5D=.NET).
If the provider you're looking for hasn't been created yet, see the [develop a provider](#develop-a-provider) section to learn how to build it yourself.
Once you've added a provider as a dependency, it can be registered with OpenFeature like this:
```csharp
await Api.Instance.SetProviderAsync(new MyProvider());
```
In some situations, it may be beneficial to register multiple providers in the same application.
This is possible using [domains](#domains), which is covered in more detail below.
### Targeting
Sometimes, the value of a flag must consider some dynamic criteria about the application or user such as the user's location, IP, email address, or the server's location.
In OpenFeature, we refer to this as [targeting](https://openfeature.dev/specification/glossary#targeting).
If the flag management system you're using supports targeting, you can provide the input data using the [evaluation context](https://openfeature.dev/docs/reference/concepts/evaluation-context).
```csharp
// set a value to the global context
EvaluationContextBuilder builder = EvaluationContext.Builder();
builder.Set("region", "us-east-1");
EvaluationContext apiCtx = builder.Build();
Api.Instance.SetContext(apiCtx);
// set a value to the client context
builder = EvaluationContext.Builder();
builder.Set("region", "us-east-1");
EvaluationContext clientCtx = builder.Build();
var client = Api.Instance.GetClient();
client.SetContext(clientCtx);
// set a value to the invocation context
builder = EvaluationContext.Builder();
builder.Set("region", "us-east-1");
EvaluationContext reqCtx = builder.Build();
bool flagValue = await client.GetBooleanValuAsync("some-flag", false, reqCtx);
```
### Hooks
[Hooks](https://openfeature.dev/docs/reference/concepts/hooks) allow for custom logic to be added at well-defined points of the flag evaluation life-cycle.
Look [here](https://openfeature.dev/ecosystem/?instant_search%5BrefinementList%5D%5Btype%5D%5B0%5D=Hook&instant_search%5BrefinementList%5D%5Bcategory%5D%5B0%5D=Server-side&instant_search%5BrefinementList%5D%5Btechnology%5D%5B0%5D=.NET) for a complete list of available hooks.
If the hook you're looking for hasn't been created yet, see the [develop a hook](#develop-a-hook) section to learn how to build it yourself.
Once you've added a hook as a dependency, it can be registered at the global, client, or flag invocation level.
```csharp
// add a hook globally, to run on all evaluations
Api.Instance.AddHooks(new ExampleGlobalHook());
// add a hook on this client, to run on all evaluations made by this client
var client = Api.Instance.GetClient();
client.AddHooks(new ExampleClientHook());
// add a hook for this evaluation only
var value = await client.GetBooleanValueAsync("boolFlag", false, context, new FlagEvaluationOptions(new ExampleInvocationHook()));
```
### Logging
The .NET SDK uses Microsoft.Extensions.Logging. See the [manual](https://learn.microsoft.com/en-us/dotnet/core/extensions/logging?tabs=command-line) for complete documentation.
### Domains
Clients can be assigned to a domain.
A domain is a logical identifier which can be used to associate clients with a particular provider.
If a domain has no associated provider, the default provider is used.
```csharp
// registering the default provider
await Api.Instance.SetProviderAsync(new LocalProvider());
// registering a provider to a domain
await Api.Instance.SetProviderAsync("clientForCache", new CachedProvider());
// a client backed by default provider
FeatureClient clientDefault = Api.Instance.GetClient();
// a client backed by CachedProvider
FeatureClient scopedClient = Api.Instance.GetClient("clientForCache");
```
Domains can be defined on a provider during registration.
For more details, please refer to the [providers](#providers) section.
### Eventing
Events allow you to react to state changes in the provider or underlying flag management system, such as flag definition changes,
provider readiness, or error conditions.
Initialization events (`PROVIDER_READY` on success, `PROVIDER_ERROR` on failure) are dispatched for every provider.
Some providers support additional events, such as `PROVIDER_CONFIGURATION_CHANGED`.
Please refer to the documentation of the provider you're using to see what events are supported.
Example usage of an Event handler:
```csharp
public static void EventHandler(ProviderEventPayload eventDetails)
{
Console.WriteLine(eventDetails.Type);
}
```
```csharp
EventHandlerDelegate callback = EventHandler;
// add an implementation of the EventHandlerDelegate for the PROVIDER_READY event
Api.Instance.AddHandler(ProviderEventTypes.ProviderReady, callback);
```
It is also possible to register an event handler for a specific client, as in the following example:
```csharp
EventHandlerDelegate callback = EventHandler;
var myClient = Api.Instance.GetClient("my-client");
var provider = new ExampleProvider();
await Api.Instance.SetProviderAsync(myClient.GetMetadata().Name, provider);
myClient.AddHandler(ProviderEventTypes.ProviderReady, callback);
```
### Shutdown
The OpenFeature API provides a close function to perform a cleanup of all registered providers. This should only be called when your application is in the process of shutting down.
```csharp
// Shut down all providers
await Api.Instance.ShutdownAsync();
```
## Extending
### Develop a provider
To develop a provider, you need to create a new project and include the OpenFeature SDK as a dependency.
This can be a new repository or included in [the existing contrib repository](https://github.com/open-feature/dotnet-sdk-contrib) available under the OpenFeature organization.
You’ll then need to write the provider by implementing the `FeatureProvider` interface exported by the OpenFeature SDK.
```csharp
public class MyProvider : FeatureProvider
{
public override Metadata GetMetadata()
{
return new Metadata("My Provider");
}
public override Task<ResolutionDetails<bool>> ResolveBooleanValueAsync(string flagKey, bool defaultValue, EvaluationContext? context = null, CancellationToken cancellationToken = default)
{
// resolve a boolean flag value
}
public override Task<ResolutionDetails<string>> ResolveStringValueAsync(string flagKey, string defaultValue, EvaluationContext? context = null, CancellationToken cancellationToken = default)
{
// resolve a string flag value
}
public override Task<ResolutionDetails<int>> ResolveIntegerValueAsync(string flagKey, int defaultValue, EvaluationContext context = null)
{
// resolve an int flag value
}
public override Task<ResolutionDetails<double>> ResolveDoubleValueAsync(string flagKey, double defaultValue, EvaluationContext? context = null, CancellationToken cancellationToken = default)
{
// resolve a double flag value
}
public override Task<ResolutionDetails<Value>> ResolveStructureValueAsync(string flagKey, Value defaultValue, EvaluationContext? context = null, CancellationToken cancellationToken = default)
{
// resolve an object flag value
}
}
```
### Develop a hook
To develop a hook, you need to create a new project and include the OpenFeature SDK as a dependency.
This can be a new repository or included in [the existing contrib repository](https://github.com/open-feature/dotnet-sdk-contrib) available under the OpenFeature organization.
Implement your own hook by conforming to the `Hook interface`.
To satisfy the interface, all methods (`Before`/`After`/`Finally`/`Error`) need to be defined.
```csharp
public class MyHook : Hook
{
public ValueTask<EvaluationContext> BeforeAsync<T>(HookContext<T> context,
IReadOnlyDictionary<string, object> hints = null)
{
// code to run before flag evaluation
}
public ValueTask AfterAsync<T>(HookContext<T> context, FlagEvaluationDetails<T> details,
IReadOnlyDictionary<string, object> hints = null)
{
// code to run after successful flag evaluation
}
public ValueTask ErrorAsync<T>(HookContext<T> context, Exception error,
IReadOnlyDictionary<string, object> hints = null)
{
// code to run if there's an error during before hooks or during flag evaluation
}
public ValueTask FinallyAsync<T>(HookContext<T> context, IReadOnlyDictionary<string, object> hints = null)
{
// code to run after all other stages, regardless of success/failure
}
}
```
Built a new hook? [Let us know](https://github.com/open-feature/openfeature.dev/issues/new?assignees=&labels=hook&projects=&template=document-hook.yaml&title=%5BHook%5D%3A+) so we can add it to the docs!
<!-- x-hide-in-docs-start -->
## ⭐️ Support the project
- Give this repo a ⭐️!
- Follow us on social media:
- Twitter: [@openfeature](https://twitter.com/openfeature)
- LinkedIn: [OpenFeature](https://www.linkedin.com/company/openfeature/)
- Join us on [Slack](https://cloud-native.slack.com/archives/C0344AANLA1)
- For more information, check out our [community page](https://openfeature.dev/community/)
## 🤝 Contributing
Interested in contributing? Great, we'd love your help! To get started, take a look at the [CONTRIBUTING](CONTRIBUTING.md) guide.
### Thanks to everyone who has already contributed
[](https://github.com/open-feature/dotnet-sdk/graphs/contributors)
Made with [contrib.rocks](https://contrib.rocks).
<!-- x-hide-in-docs-end -->