How to Implement VoIP in iOS: A Guide to CallKit, PushKit, and AVAudioSession

In the world of mobile apps, Voice over IP (VoIP) has become a standard way to enable voice communication, allowing users to make calls over the Internet instead of traditional phone networks. If you’re looking to integrate VoIP into your iOS app, Apple provides several key frameworks, such as CallKit, PushKit, and AVAudioSession, to help you deliver a seamless experience.

In this post, we’ll walk through the essential steps to build a basic VoIP app, including setting up incoming and outgoing calls, managing call events, and configuring audio sessions for optimal voice quality.

Key Frameworks for VoIP in iOS

Before we dive into the code, it’s important to understand the primary frameworks you’ll need for VoIP on iOS:

• CallKit: Manages the call UI, allowing your VoIP app to integrate with the native phone experience.
• PushKit: Handles VoIP push notifications, enabling the app to wake up for incoming calls, even when it’s in the background.
• AVAudioSession: Manages audio playback and recording, essential for controlling the audio input/output during VoIP calls.

With that foundation in mind, let’s explore how to use these frameworks in practice.

Step 1: Configure CallKit for VoIP

The CallKit framework provides a familiar, native interface for handling calls in your VoIP app. It makes your app look and behave like the standard phone app, allowing you to display incoming and outgoing calls using the same UI.

Here’s how to set up a basic CXProvider to manage incoming and outgoing calls:

import CallKit

class VoIPCallManager {
    let callController = CXCallController()
    let provider: CXProvider

    init() {
        let configuration = CXProviderConfiguration(localizedName: "Your App Name")
        configuration.supportsVideo = true
        configuration.maximumCallsPerCallGroup = 1
        configuration.supportedHandleTypes = [.phoneNumber]

        provider = CXProvider(configuration: configuration)
        provider.setDelegate(self, queue: nil)
    }

    func reportIncomingCall(uuid: UUID, handle: String) {
        let update = CXCallUpdate()
        update.remoteHandle = CXHandle(type: .phoneNumber, value: handle)
        update.hasVideo = false

        provider.reportNewIncomingCall(with: uuid, update: update) { error in
            if let error = error {
                print("Error reporting incoming call: \(error.localizedDescription)")
            }
        }
    }
}

extension VoIPCallManager: CXProviderDelegate {
    func providerDidReset(_ provider: CXProvider) {
        // Handle any cleanup when the call provider is reset
    }

    func provider(_ provider: CXProvider, perform action: CXAnswerCallAction) {
        // Handle the call answer event
        action.fulfill()
    }

    func provider(_ provider: CXProvider, perform action: CXEndCallAction) {
        // Handle the call end event
        action.fulfill()
    }
}        

This code sets up VoIPCallManager, which reports new incoming calls using the familiar native call UI. It also allows for call actions, such as answering or ending the call, using the CXProviderDelegate methods.

Step 2: Use PushKit for VoIP Notifications

One of the key challenges in VoIP apps is receiving calls when your app isn’t running in the foreground. PushKit allows you to handle VoIP push notifications, which wake up the app and prepare it to handle an incoming call.

Here’s how to implement PushKit:

import PushKit

class PushKitDelegate: NSObject, PKPushRegistryDelegate {
    let voipRegistry: PKPushRegistry

    override init() {
        voipRegistry = PKPushRegistry(queue: .main)
        super.init()
        voipRegistry.delegate = self
        voipRegistry.desiredPushTypes = [.voIP]
    }

    // This method is called when a VoIP push notification is received
    func pushRegistry(_ registry: PKPushRegistry, didReceiveIncomingPushWith payload: PKPushPayload, for type: PKPushType) {
        let uuid = UUID()
        let handle = "CallerNameOrNumber" // This would typically come from the payload
        VoIPCallManager().reportIncomingCall(uuid: uuid, handle: handle)
    }

    // Register for VoIP push notifications
    func pushRegistry(_ registry: PKPushRegistry, didUpdate pushCredentials: PKPushCredentials, for type: PKPushType) {
        // Send the push token to the server to be used for VoIP calls
        let deviceToken = pushCredentials.token.reduce("") { $0 + String(format: "%02.2hhx", $1) }
        print("VoIP Push Token: \(deviceToken)")
    }
}        

In this example, the app receives a VoIP push notification and wakes up to handle the call, passing the payload data to VoIPCallManager. This ensures that your app is notified about calls even when it’s in the background.

Step 3: Configure AVAudioSession for Call Audio

To ensure that audio is handled properly during calls, you’ll need to configure AVAudioSession. This framework lets you manage audio routing and control the microphone and speaker settings for voice communication.

Here’s a basic setup for configuring the audio session when a call is started:

import AVFoundation

func configureAudioSession() {
    let session = AVAudioSession.sharedInstance()
    do {
        try session.setCategory(.playAndRecord, mode: .voiceChat, options: [.allowBluetooth])
        try session.setActive(true)
    } catch {
        print("Failed to configure AVAudioSession: \(error.localizedDescription)")
    }
}        

This configuration optimizes the audio session for VoIP calls by enabling playback and recording, while also allowing for Bluetooth headset support.

Step 4: Handling Outgoing Calls

To initiate outgoing VoIP calls, you can use CXCallController from CallKit. The following code shows how to handle an outgoing call request:

func startOutgoingCall(handle: String) {
    let uuid = UUID()
    let handle = CXHandle(type: .phoneNumber, value: handle)
    let startCallAction = CXStartCallAction(call: uuid, handle: handle)
    let transaction = CXTransaction(action: startCallAction)

    callController.request(transaction) { error in
        if let error = error {
            print("Error starting outgoing call: \(error.localizedDescription)")
        } else {
            self.configureAudioSession()
        }
    }
}        

This code sends an outgoing call request to CallKit and configures the audio session to handle the call audio.

Step 5: Background Modes for VoIP

To ensure your VoIP app can receive calls when in the background, you need to enable background modes in Xcode:

1. Open Xcode > Project Settings > Capabilities.
2. Enable Background Modes.
3. Check the options for Voice over IP and Audio, AirPlay, and Picture in Picture.

Conclusion

By combining CallKit, PushKit, and AVAudioSession, you can build a robust VoIP app for iOS that integrates seamlessly with the system and provides users with a familiar experience. Whether you’re handling incoming calls with PushKit or configuring audio routing with AVAudioSession, these frameworks give you the tools to deliver high-quality voice communication over the internet.

Integrating VoIP into your iOS app is easier than ever, and with the right setup, your users will be making calls in no time! Happy coding! ????