callkit

# CallKit

Build VoIP calling features that integrate with the native iOS call UI using
CallKit and PushKit. Covers incoming/outgoing call flows, VoIP push
registration, audio session coordination, and call directory extensions.
Targets Swift 6.3 / iOS 26+.

## Contents

- [Setup](#setup)
- [Provider Configuration](#provider-configuration)
- [Incoming Call Flow](#incoming-call-flow)
- [Outgoing Call Flow](#outgoing-call-flow)
- [PushKit VoIP Registration](#pushkit-voip-registration)
- [Audio Session Coordination](#audio-session-coordination)
- [Call Directory Extension and Manager](#call-directory-extension-and-manager)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#references)

## Setup

### Project Configuration

1. Enable the **Voice over IP** background mode in Signing & Capabilities
2. Add the **Push Notifications** capability
3. For call directory extensions, add a **Call Directory Extension** target

### Key Types

| Type | Role |
|---|---|
| `CXProvider` | Reports calls to the system, receives call actions |
| `CXCallController` | Requests call actions (start, end, hold, mute) |
| `CXCallUpdate` | Describes call metadata (caller name, video, handle) |
| `CXProviderDelegate` | Handles system call actions and audio session events |
| `PKPushRegistry` | Registers for and receives VoIP push notifications |
| `PKVoIPPushMetadata` | iOS 26.4+ metadata that says whether a VoIP push must be reported |

## Provider Configuration

Create a single `CXProvider` at app launch and keep it alive for the app
lifetime. Configure it with a `CXProviderConfiguration` that describes your
calling capabilities.

```swift
import CallKit

/// CXProvider dispatches all delegate calls to the queue passed to `setDelegate(_:queue:)`.
/// The `let` properties are initialized once and never mutated, making this type
/// safe to share across concurrency domains despite @unchecked Sendable.
final class CallManager: NSObject, @unchecked Sendable {
    static let shared = CallManager()

    let provider: CXProvider
    let callController = CXCallController()

    private override init() {
        let config = CXProviderConfiguration()
        config.localizedName = "My VoIP App"
        config.supportsVideo = true
        config.maximumCallsPerCallGroup = 1
        config.maximumCallGroups = 2
        config.supportedHandleTypes = [.phoneNumber, .emailAddress]
        config.includesCallsInRecents = true

        provider = CXProvider(configuration: config)
        super.init()
        provider.setDelegate(self, queue: nil)
    }
}
```

## Incoming Call Flow

When a required VoIP call push arrives, report the incoming call to CallKit
immediately. The system displays the native call UI. You must report required
calls before the PushKit completion handler returns -- failure to do so causes
the system to terminate your app.

```swift
func reportIncomingCall(
    uuid: UUID,
    handle: String,
    hasVideo: Bool
) async throws {
    let update = CXCallUpdate()
    update.remoteHandle = CXHandle(type: .phoneNumber, value: handle)
    update.hasVideo = hasVideo
    update.localizedCallerName = "Jane Doe"

    try await withCheckedThrowingContinuation {
        (continuation: CheckedContinuation<Void, Error>) in
        provider.reportNewIncomingCall(
            with: uuid,
            update: update
        ) { error in
            if let error {
                continuation.resume(throwing: error)
            } else {
                continuation.resume()
            }
        }
    }
}
```

### Handling the Answer Action

Implement `CXProviderDelegate` to respond when the user answers:

```swift
extension CallManager: CXProviderDelegate {
    func providerDidReset(_ provider: CXProvider) {
        // End all calls, reset audio
    }

    func provider(_ provider: CXProvider, perform action: CXAnswerCallAction) {
        // Prepare audio, then fulfill only after the call is actually ready
        configureAudioSession()
        connectToCallServer(callUUID: action.callUUID) { success in
            if success {
                action.fulfill()
            } else {
                provider.reportCall(
                    with: action.callUUID,
                    endedAt: Date(),
                    reason: .failed
                )
                action.fail()
            }
        }
    }

    func provider(_ provider: CXProvider, perform action: CXEndCallAction) {
        disconnectFromCallServer(callUUID: action.callUUID)
        action.fulfill()
    }
}
```

## Outgoing Call Flow

Use `CXCallController` to request an outgoing call. The system routes the
request through your `CXProviderDelegate`.

```swift
func startOutgoingCall(handle: String, hasVideo: Bool) {
    let uuid = UUID()
    let handle = CXHandle(type: .phoneNumber, value: handle)
    let startAction = CXStartCallAction(call: uuid, handle: handle)
    startAction.isVideo = hasVideo

    let transaction = CXTransaction(action: startAction)
    callController.request(transaction) { error in
        if let error {
            print("Failed to start call: \(error)")
        }
    }
}
```

### Delegate Methods for Outgoing Calls

```swift
extension CallManager {
    func provider(_ provider: CXProvider, perform action: CXStartCallAction) {
        configureAudioSession()
        // Begin connecting to server
        provider.reportOutgoingCall(
            with: action.callUUID,
            startedConnectingAt: Date()
        )

        connectToServer(callUUID: action.callUUID) {
            provider.reportOutgoingCall(
                with: action.callUUID,
                connectedAt: Date()
            )
        }
        action.fulfill()
    }
}
```

## PushKit VoIP Registration

Register for VoIP pushes at every app launch and send token changes to your
server. For iOS 13 SDK+ apps, every report-required VoIP call push must be
reported before PushKit completion using CallKit, or LiveCommunicationKit fo