una-mobile-app/ios/OneSignalNotificationServiceExtension/NotificationService.swift

import UserNotifications

import OneSignal

class NotificationService: UNNotificationServiceExtension {
    
    var contentHandler: ((UNNotificationContent) -> Void)?
    var receivedRequest: UNNotificationRequest!
    var bestAttemptContent: UNMutableNotificationContent?
    
    override func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
        self.receivedRequest = request
        self.contentHandler = contentHandler
        self.bestAttemptContent = (request.content.mutableCopy() as? UNMutableNotificationContent)
        
        if let bestAttemptContent = bestAttemptContent {
            //If your SDK version is < 3.5.0 uncomment and use this code:
            /*
            OneSignal.didReceiveNotificationExtensionRequest(self.receivedRequest, with: self.bestAttemptContent)
            contentHandler(bestAttemptContent)
            */
            
            /* DEBUGGING: Uncomment the 2 lines below to check this extension is excuting
                          Note, this extension only runs when mutable-content is set
                          Setting an attachment or action buttons automatically adds this */
            //OneSignal.setLogLevel(.LL_VERBOSE, visualLevel: .LL_NONE)
            //bestAttemptContent.body = "[Modified] " + bestAttemptContent.body
            
            OneSignal.didReceiveNotificationExtensionRequest(self.receivedRequest, with: bestAttemptContent, withContentHandler: self.contentHandler)
        }
    }
    
    override func serviceExtensionTimeWillExpire() {
        // Called just before the extension will be terminated by the system.
        // Use this as an opportunity to deliver your "best attempt" at modified content, otherwise the original push payload will be used.
        if let contentHandler = contentHandler, let bestAttemptContent =  bestAttemptContent {
            OneSignal.serviceExtensionTimeWillExpireRequest(self.receivedRequest, with: self.bestAttemptContent)
            contentHandler(bestAttemptContent)
        }
    }
    
}