Microsoft.FeatureManagement Updates

The packages associated with this release are

• Microsoft.FeatureManagement 2.0.0-preview-010610001-1263
• Microsoft.FeatureManagement.AspNetCore 2.0.0-preview-010610001-1263

Major Version Bump

This release introduces some new features and some breaking changes, thus the major version has been bumped to 2.

Features

Async Feature Filters

Support for async feature filters has been added. This results in the entire feature management pipeline being asynchronous. Async feature filters pave the way to performing async workloads in feature filters if desired.

Before

IFeatureManager fm;

if (fm.IsEnabled("MyFeature"))
{

}

After

IFeatureManager fm;

if (await fm.IsEnabledAsync("MyFeature"))
{

}

Floating Context Support

The original design for the feature management library relied on applications to have an ambient context. An application's ambient context could be used in feature filters to obtain information such as user identity and other information relevant when toggling features. This led to a disconnect in console applications which do not have an ambient context in most cases. Now application's without an ambient context can float a context into the feature management system by using the new IFeatureManager.IsEnabledAsync<TContext>(string feature, TContext context) method. The context parameter is able to be consumed by feature filters that implement IContextualFeatureFilter.

Consumption

The ability to pass a context when evaluating a feature has been added to IFeatureManager.

IFeatureManager fm = services.GetRequiredService<IFeatureManager>();

await fm.IsEnabledAsync("featureName", new MyApplicationContext
{
  UserId = "someUser"
});

Contextual Feature Filters

Contextual feature filters are feature filters that can utilize a context provided by the application when evaluating whether a feature is on or off. Contextual feature filters are a generic type. Their generic type parameter describes the interface that the passed in context must implement for the filter to be able to evaluate it.

As an example, IContextualFeatureFilter<IAccountContext> requires a context that implements IAccountContext to be passed in. If a feature is checked for enabled and a context is provided that does not implement IAccountContext then the previously mentioned filter would not run.

IFeatureFilterMetadata

With the introduction of IContextualFeatureFilter there are now two types of feature filters including IFeatureFilter. The two types of feature filters both inherit IFeatureFilterMetadata. IFeatureFilterMetadata is a marker interface and does not actually provide any feature filtering capabilities. It is used as the new parameter type for IFeatureManagementBuilder.AddFeatureFilter.

Breaking Changes

• IFeatureManager.IsEnabled is now asynchronous
  • IsEnabled was renamed to IsEnabledAsync.
  • IFeatureManagerSnapshot.IsEnabled is also affected.
• IFeatureFilter.Evaluate is now asynchronous
  • Evaluate was renamed to EvaluateAsync.
• Mvc.Filters.FilterCollection.AddForFeature now only accepts
  IAsyncActionFilter rather than any type of filter.
• AddRouteForFeature has been removed.
• ISessionManager is now an async interface.