# AccessoryFeatureRuntimeSessionHandler A protocol that receives events from a transport extension’s feature session. ``` protocol AccessoryFeatureRuntimeSessionHandler : Sendable ``` ## Overview Conform to this protocol in your transport extension to respond to the [`AccessoryFeatureRuntimeSession`](/documentation/AccessoryTransportExtension/AccessoryFeatureRuntimeSession) life cycle and incoming data. The system creates an instance of your type from the handler factory closure that you pass to [`makeFeatureSession(_:)`](/documentation/AccessoryTransportExtension/AccessoryTransportSession/makeFeatureSession(_:)). A handler that serves one feature can’t serve another because each feature pins the `Session` associated type through its own `Handler` type alias (for example, [`AccessoryWorker.FeatureSession.Handler`](/documentation/AccessoryTransportExtension/AccessoryWorker/FeatureSession/Handler)). Implement the only required method, [`sessionStarted(_:)`](/documentation/AccessoryTransportExtension/AccessoryFeatureRuntimeSessionHandler/sessionStarted(_:)), to send data. ## Topics ### Handling the session life cycle [`func sessionStarted(Self.Session)`](/documentation/AccessoryTransportExtension/AccessoryFeatureRuntimeSessionHandler/sessionStarted(_:)) Notifies the handler when its feature session starts. [`func sessionInvalidated(error: (any Error)?)`](/documentation/AccessoryTransportExtension/AccessoryFeatureRuntimeSessionHandler/sessionInvalidated(error:)) Notifies the handler when its feature session ends. ### Receiving data [`func dataReceived(Data) async throws`](/documentation/AccessoryTransportExtension/AccessoryFeatureRuntimeSessionHandler/dataReceived(_:)) Handles data that the data provider extension sends. ### Associated Types [`associatedtype Session : AccessoryFeatureRuntimeSession`](/documentation/AccessoryTransportExtension/AccessoryFeatureRuntimeSessionHandler/Session) A session type that the handler serves. ## Relationships ### Inherits From [`SendableMetatype`](/documentation/Swift/SendableMetatype) [`Sendable`](/documentation/Swift/Sendable) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)