One-to-one video call using CallKit and PushKit with flutter iOS app.

We need to use CallKit to handle incoming VoIP notifications from iOS 13. Check the WWDC2019 video for more information. So instead of using CallKit and PushKit separately, there is a growing need to use them together. However, there are still few VoIP notification samples on the net that use CallKit and PushKit (especially for Flutter). I decided to create a flutter plugin with the minimum required functions. You can use this plugin, but the actual purpose is to help you create a VoIPKit tailored to your service.

• iOS only, not support Android.
• iOS 10 or above.
• one-to-one call only, not support group call.
• need to a server for pushing VoIP notification with APNs.
• to actually make a video or call, you need to link to a service such as WebRTC（ex: Agora, SkyWay, Amazon Kinesis Video Streams）.

• Add flutter_ios_voip_kit as a dependency in your pubspec.yaml file.

1. Select Background Modes > Voice over IP and Remote notifications is ON.
2. Select Push Notifications.
3. Changed ios/Runner/Info.plist after selected Capability.

<key>UIBackgroundModes</key>
<array>
    <string>remote-notification</string>
    <string>voip</string>
</array>

• Edit ios/Runner/Info.plist as below.

<key>FIVKIconName</key>
<string>AppIcon-VoIPKit</string>
<key>FIVKLocalizedName</key>
<string>VoIP-Kit</string>
<key>FIVKSupportVideo</key>
<true/>
<key>FIVKSkipRecallScreen</key>
<true/>

• Add an icon（.png or .pdf） ios/Runner/Assets.xcassets/AppIcon-VoIPKit to use on the screen when a call comes in while locked iPhone.

• Visit the Apple Developer https://developer.apple.com/certificates and create a new VoIP Services Certificate(.cer). Check Voice Over IP (VoIP) Best Practices Figure 11-2 for more information.
• Create .p12 from .cer with KeyChainAccess, and .pem with openssl.

Create .p12 from .cer with KeyChainAccess

openssl pkcs12 -in voip_services.p12 -out voip_services.pem -nodes -clcerts

• See Apple document.
• https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/sending_notification_requests_to_apns
• Add data(payload) like a below.

{
    "aps": {
        "alert": {
          "uuid": <Version 4 UUID (e.g.: https://www.uuidgenerator.net/version4) >,
          "incoming_caller_id": <your service user id>,
          "incoming_caller_name": <your service user name>,
        }
    }
}

• You can use curl to test VoIP notifications as follows.

curl -v \
-d '{"aps":{"alert":{"uuid":"982cf533-7b1b-4cf6-a6e0-004aab68c503","incoming_caller_id":"0123456789","incoming_caller_name":"Tester"}}}' \
-H "apns-push-type: voip" \
-H "apns-expiration: 0" \
-H "apns-priority: 0" \
-H "apns-topic: <your app’s bundle ID>.voip" \
--http2 \
--cert ./voip_services.pem \
https://api.sandbox.push.apple.com/3/device/<VoIP device Token for your iPhone>

• It is possible to try the example app with some features without a server.
• There is also a example that can confirm the operation of flutter_ios_voip_kit using SkyWay

Select call role	🤙 Caller page	🔔 Callee page

🔔 Callee(incoming call)	🔔 Callee(locked)	🔔 Callee(locked)	🔔 Callee(recall)

🔔 Callee(unanswered local notification)	🔔 Callee(unanswered local notification)

• No. CallKit support incoming call screen only. You need to make your own a call and outgoing call screens.

• No. Since the specifications of VoIP token and push token are different, it is necessary to manage them separately in your database.

• Please uninstall the app, restart the terminal and reinstall the app. You can get it after a while.

• Please check the following items.
  1. Is the VoIP device token correct?
  2. Did you set your app’s bundle ID with .voip to apns-topic?
  3. Did you set voip to apns-push-type?
  4. Is the APNs endpoint（Development or Production） correct?
  5. For iOS13, VoIP notifications may not be received if call kit call fails many times. Please uninstall the app, restart the terminal and reinstall the app.

• The icon image should be a square with side length of 40 points. The color is ignored. Please design with the difference of alpha.
• If created in PDF, checked Preserve Vector Data for Resizing and change Single Scale for Scales.

create icon (e.g.: sketch)	Xcode Image Set

• https://developer.apple.com/documentation/callkit
• https://developer.apple.com/documentation/pushkit
• https://developer.apple.com/documentation/callkit/making_and_receiving_voip_calls_with_callkit