iOS 13 PushKit VoIP restrictions breaking SIP VoIP apps

Hi,


We are a fairly large company providing smartphone and desktop applications for VoIP/UC together with PBX systems, on-premise as well as clourd offerings. All our app are talking to the telephony servers over SIP.

Up unitl now, our flow on iOS was:

  1. Receive PushKit VoIP notification
  2. REGISTER towards telephony server
  3. Receive INVITE
  4. reportIncomingCall


With the changes enforced and outlined in https://developer.apple.com/videos/play/wwdc2019/707/, the whole SIP concept will break.

We are now forced to report an incoming call so early that the user might accept the call before the REGISTER has completed and an INVITE has been received which will lead to a pretty bad user experience.

Even worse, we will report an incoming call even if there is no actual call. This might happen as the call has already been canceled on the remote end and we won't get an INVITE. Or if the registration fails due to network issues that prevents us from reaching the telephony server.


How does Apple expect us to deal with these situations?

It's not possible to perform the whole REGISTER/INVITE stuff "in the same run loop as pushRegistry:didReceiveIncomingPushWithPayload:forType:[withCompletionHandler:] without delay."


I'm not sure what our support and sales guys will do when they receive negative customer feedback with the changed implementation. Maybe tell existing and new customers to use Android smartphones instead of iPhones...


There has to be at least some way of delaying the reportIncomingCall so that an application can check against the telephony server if there is a call and report if there is none to avoid punishment for not reporting the call.

32 Replies

A lot of different issues have been raised in this thread, so I've loosely summarized them to the following 4 questions issues:



1) Reporting a call immediately does not work with the SIP register-invite flow


On iOS 13, there are cases where you will need to initiate a CallKit call that you previously would have silently ignored. However, in practice, this should not be the common case, particularly for truly “non-existent" calls, since that would mean you had been notifying the user of calls that did not exist.


The more common cases here are calls that have either already ended (because the caller hung up) or can't be completed (because network conditions prevent the call from connecting). While calls will be created for both of these cases, there are few different techniques that you can use to mitigate any disruptions:


While you must report an incoming call immediately, you are still free to decide the call has failed and tell the system later, asynchronously. To do this, call reportCallWithUUID:endedAtDate:reason:. This will tear down the incoming call UI even if the user has not answered the call.


If the user is particularly fast at tapping the accept call button, or if the network conditions are poor or there is otherwise a lot of latency, then you should simply wait until the necessary handshakes are complete before calling fulfill on the CXAnswerCallAction. To the user, it simply appears that the call is taking some time to connect, which is a common experience even with standard phone calls.


Note that the system takes a few seconds for the incoming call UI to animate in, during which the app has the opportunity to complete this handshake, so this will only have a user-visible impact if it takes a significant time for the handshake to complete.


At any time, you can asynchronously update the UI with the reportCallWithUUID:updated: API. That means that if you cannot put the caller ID info in the push payload, you can simply choose to present dummy information (like "Connecting Call..." for the caller name) and update it asynchronously once they get the real information from your server.


2) Sending a push to cancel an incoming call


While your app currently has an active call (ringing or answered), your app is not required to create additional calls for VoIP pushes received during this call. This is intended to be used to support advanced functionality like dynamic call priority, but it could also be used to cancel an incoming call.


Having said that, this is not an approach I would recommend or rely upon. The reality is that as soon as your app receives it's PushKit notification it should be connecting to your server, so unless network conditions are very poor, you should be able to communicate to your client through that connection faster than PushKit. More to the point, if network conditions mean that you can't connect to your server, then trying to handle this with another push isn't a great idea either, since poor connectivity (and timing generally) opens the door to edge cases you'd want to avoid - for example, a client receiving ONLY the cancelation and not the original call notification.


As a side note here, keep in mind that as part of adapting to the new requirements you'll want to make sure the VoIP notification has a short or zero "apns-expiration" to prevent newly available devices from being notified of out-of-date calls. This will also minimize the cancelation issue, since a “newly available device" (for example, a phone that was just powered on) will ONLY receive notifications about calls that are occurring at that particular instant.


3) Block-lists/Do Not Disturb


CallKit respects the system Do Not Disturb setting, so most apps will not have to worry about system-level Do Not Disturb functionality. If your app has it's own blocking/do not disturb system built in, you can also maintain that list server-side and not send pushes to the blocked devices. If you absolutely need to do "local" call blocking, then you can report a call and then end it. The call will be briefly visible to the user, but you can also configure the source of the call to communicate what's going on ("Blocked Call...").


4) Using VoIP pushes to trigger syncs or other non-VoIP use cases


VoIP pushes were always intended to specifically support call notifications and nothing else. The good news here is that using Notification Service Extension is the best substitute for most of the functionality that you previously handled with PushKit:


https://developer.apple.com/documentation/usernotifications/unnotificationserviceextension


A few examples:

  • For general messaging, you can connect to your server in the extension delegate, download any missed messages, and then update the notification content as appropriate.
  • The same approach can be used to tell the user about calls missed while the device was offline and/or pending voicemails.
  • For non-user facing functionality, like data synchronization or other app maintenance, I would recommend checking out the new BackgroundTasks framework:


https://developer.apple.com/documentation/backgroundtasks


Kevin Elliott

Developer Technical Support

Core OS/Hardware

Hi,

No answers but some more information.

We're experiencing all the same issues. Besides the risk of ghost calls we're finding that limiting the PushKit notifications is preventing us from implementing features of some other well known messaging/voip apps; exactly as others have mentioned.

One feature in particular for us kicked this off. How to mute a group chat/channel and not show any notifications. Yes we could have the server do it but it seemed simpler to have the client do it. So we started investigating how other apps did this. It lead to something interesting.

WhatsApp is a great example of a feature-rich messaging app and we always start these conversations with "what does WhatsApp do". When we looked we saw that it is using PushKit notifications in a seemingly unrestricted fashion. What does that mean? It appears to be using PushKit notifications for sending messages. Something that I'd have considered impossible given the restrictions in place. So we thought maybe it's still using Xcode10? We find that highly unlikely given the looming cut-off date. So a bit of digging (not that much when you consider the link and the question I asked)

https://stackoverflow.com/questions/60815763/how-does-the-whatsapp-web-client-still-work-with-the-latest-ios-update-sdk-vers

This specific entitlement seems to be the reason that they are allowed to not report an incoming call:
com.apple.developer.pushkit.unrestricted-voip
I can't find any documentation regarding this entitlement, so I'm pretty sure they have been given a special permission by Apple.

So we started looking for this entitlement. Lookup source-code-walkthrough-of-telegram-ios-part-3-other-foundations-66ace05954a4 (the editor is refusing to let me post the URL)

As any abuse could cause a significant battery drain problem, Apple started to require apps to invoke CallKit after receiving VoIP notifications since the iOS SDK 13. But Telegram-iOS seems to survive from the new rule as it has got a special entitlement from Apple: com.apple.developer.pushkit.unrestricted-voip. The same undocumented entitlement can also be found in SignalApp.

So there does appear to be an entitlement available that provides seemingly unrestricted use of PushKit.

I completely understand why Apple wanted to restrict this feature but they should have vetted the apps and allowed access to trustworthy apps in a fashion similar to Critical Alerts. I'd be very happy to explain why we needed unrestricted voip and be prepared to justify it every so often. I'm slightly annoyed, but not surprised, that some apps seem to receive more access to the platform.

So I suggest you start asking your nearest Apple dealer about com.apple.developer.pushkit.unrestricted-voip.

Regards





3) Block-lists/Do Not Disturb

...

If you absolutely need to do "local" call blocking, then you can report a call and then end it. The call will be briefly visible to the user, but you can also configure the source of the call to communicate what's going on ("Blocked Call...").


Is that a good practice?Sound really bad.


Two more questions:

1.My device receive a native incoming call and the call is stil ringing, then another voip call come in, And I need to report new incoming call according to the 707 session, what will happen? In my test, sometimes callkit screen present a "Call Failed" alert.

2. My app support mutiple calls(2 calls), when the 3rd call comes, push server still sends me incoming call push, what should I do, report the call and hang it up?

3.And our app also support meetings. And we don't support call and meeting in the same time. So when I'm in call status, meeting comes in, I also need to report it and hang it up. ***???


Seriously,

"Repeatedly failing to report calls may prevent your app from receiving any more incoming call notifications".

This make everything worse.

In my opinion those changes are a step back in the user experience. So far, the CallKit was greatly above its competitiors, namely android since it is highly fractured and their VoIP call handling is messy and causes a lot of bugs. However, I'm affraid these changes will cause situations where the user may think their application is bugged when in fact it is caused by API changes.


"If the user is particularly fast at tapping the accept call button, or if the network conditions are poor or there is otherwise a lot of latency, then you should simply wait until the necessary handshakes are complete before calling fulfill on the CXAnswerCallAction. To the user, it simply appears that the call is taking some time to connect, which is a common experience even with standard phone calls"


This is true IF the phone is locked. However, since every application has to implement a UI for the incoming calls (as the CallKit/native UI only remains active in lock state) a situation may occour where a user is using the phone, receives a call, picks the call up when in fact the VoIP call is not even connected, which will possibly cause the user to think it was a "ghost call", since nothing happens except (probably) the VoIP application opens up to the normal screen until the actual call arrives and triggers the incoming call UI.


I know this may seem an extreme case but in several places, ex: in Portugal, where there is not 4G cover everywhere and some even cause a fallback to GSM, this may me more common than the standard user experience.


I believe these changes only make sense IF the CallKit also fully enabled the native UI either for incoming or outgoing calls which would not lead to UI transitions and hide the fact that we are notifying the user for a call that might not have arrived yet.

Hi! Voip-push started an app on ios12. What do I need to do to keep the same behavior on iOS 13? Do I need to add an apns-expiration<=5 parameter to the push payload and that's it?

Hi langaCom


We too are in EXACTLY the same situation with iOS13.


I would echo your question ...


How does Apple expect us to deal with these situations?

It's not possible to perform the whole REGISTER/INVITE stuff "in the same run loop as pushRegistry:didReceiveIncomingPushWithPayload:forType:[withCompletionHandler:] without delay."


We have built a business which since the introduction of callkit and pushkit gives a great VoIP user experience. (Much better than Android) Now huge architectural changes (ie not using standard VoIP Register/ Invite) are required to be implemented somehow in a rush for iOS13 release.


I would urge Apple to please shelve or scrap this change. Genuine VoIP Apps will be hit badly

If I build my App using Xcode10, it works well on iOS13. But if I build it by Xcode11, call failed alert will pop up.

I write a simple demo only contain PushKit code. This bug still happens.

I submited a feedback on Sep 2, but still didn't get any response.

Also I submit a DTS recently and still wait for the solution.

Does any other developers experience the same "Call Failed" alert?

Hi,

Firstly thank you for this information,

Secondly, You mentioned not needing to report new calls when we already have a ringing or active call.
What happens if we get two voip pushes at the same time, for example from two different callers.
From our testings, (Xcode 10, not 11 yet) when the second push arrives, we still do not have an active or ringing call reported from the first push. Do we need to still report a call for the second push? Doing that resulted in both calls reporting succesfully and eventually failing after the user sometimes needing to respond to two incoming call screens one after the other.
Will this behaviour be rectified when building with xcode11?


Best Regards

Hi Kevin, thank you for your clarifications.


Can you please confirm that this requirement will only be for apps built against the iOS 13 SDK?

Existing apps, built with the iOS 12 SDK will work as before when running on iOS 13?


Thanks in advance

I have one more question not covered here yet: What about calls showing up in system's Phone app in Recents?

What if we immediately show CallKit UI with a placeholder "Connecting Call..." in place of the caller's name, but then end the call before the user answers, either because the call already ended or whatever other reason (in our app, calls can only be received if user is connected to his home's WiFi)? Won't there be a "Connecting Call..." in recent calls in system app that we can't even call back to because we never got the number of the person who could have been calling us?

This is an extremely disappointing change that WILL result in degraded user experience. We're developing an XMPP application, and this affects us greatly. We even added an honest VoIP functionality to have legal access to silent VoIP notifications, because standard silent push notifications are extremely unreliable and bad.

Hi KevinE,



So, my understanding is:

1) For iOS 13, Apple still support VOIP push.

2) App integrated with the PushKit must calls the [CXProvider reportNewIncomingCallWithUUID:] in the didReceiveIncomingPushWithPayload: forType: method. Right?

BTW, my device (iPhoneXs Max, 13.0) can not receive any VOIP push on 11th. Oct in China. Do the VOIP push service is pending for some reason?

We are in a similar situation. Like the post above, the user may answer the call before the app is ready to receive the call.


In addition, there may be cases where a VOIP notification is received and we do not want to trigger the incoming call UI. For example:


  • A local settings (i.e., call block or app-level do-not-disturb) indicates that the user does not want to receive the call.
  • Other situations where a VOIP notification might be sent to trigger a critical sync between devices.


Our concern is that these use cases could result in the notificaton not getting reported to CallKit and potentially trigger a violation on iOS 13. What is the recommendation for these use cases?

>> Even worse, we will report an incoming call even if there is no actual call.


I too am very interested in what Apple have to say about this.


Also what are your thoughts on blocking calls? Does your app currenlty permit users of the app to block certain numbers? I don't see how an app-side blocking mechanism could possibly work now because the call screen will always be displayed (previously the app could just ignore any voip pushes for blocked numbers, now this is no longer possible)

+1 with the exact same issue. We contacted Apple and got a generic and useless "check App Store Guidelines" answer, we cannot submit a TSI for beta software and there's no official answer here on the forums by Apple.


If Apple really wants to prevent the misuse of VoIP pushes, why not limit their access to a special entitlement, like they did on the Critical Alerts feature?


I would very much like to know how are the "big players" like WhatsApp, Messenger, etc going to deal with this change...