Reliable Background Data Upload in Mobile Apps

let config = URLSessionConfiguration.background( withIdentifier: "com.myapp.upload.\(UUID().uuidString)" ) config.isDiscretionary = false // upload immediately, not deferred config.sessionSendsLaunchEvents = true // wake app on completion let session = URLSession( configuration: config, delegate: self, delegateQueue: nil ) 

For background upload, use only uploadTask(with:fromFile:). Save the data to a file beforehand. uploadTask(with:from:) with Data does not work in the background—data is lost on restart.

Note: when upload completes or the app is killed, iOS calls application(_:handleEventsForBackgroundURLSession:completionHandler:) in AppDelegate. You need to restore the session with the same identifier and call the completionHandler after processing events. Mistake: creating a new session with a new identifier on each launch—events will be lost.

Tracking progress and notifications on iOS

Upload progress is obtained via the delegate urlSession(_:task:didSendBodyData:totalBytesSent:totalBytesExpectedToSend:). In the background, you cannot update the UI, so show progress via UNMutableNotificationContent with progress. On completion, send a local notification:

let content = UNMutableNotificationContent() content.title = "Upload complete" content.body = "20 photos uploaded successfully" let request = UNNotificationRequest( identifier: UUID().uuidString, content: content, trigger: nil ) UNUserNotificationCenter.current().add(request) 

How does background upload work on Android?

On Android, we use WorkManager with CoroutineWorker. For large files, we implement chunking: the file is split into parts, each uploaded with a separate request containing the Content-Range header. If the upload is interrupted, we resume from the last successful chunk.

class UploadWorker(context: Context, params: WorkerParameters) : CoroutineWorker(context, params) { override suspend fun doWork(): Result { val filePath = inputData.getString("file_path") ?: return Result.failure() return try { uploadFile(File(filePath)) Result.success() } catch (e: Exception) { if (runAttemptCount < 3) Result.retry() else Result.failure() } } } 

runAttemptCount + Result.retry() — automatic retries on failure with backoff strategy. Set the maximum number of attempts: optimally 3-5.

Why is Foreground Service needed for large files?

For uploading large files (videos, archives) on Android, ForegroundService is mandatory—the system will not kill the process while the service shows a notification. WorkManager can delegate the task to Foreground via setForeground(). On Android 14+, ForegroundService type dataSync requires an explicit permission in the manifest. This increases upload success rate to 99% even with unstable connections.

Comparison of iOS and Android approaches

Step-by-step: configuring retries in WorkManager

1. Set the maximum number of attempts in configuration: setBackoffCriteria(BackoffPolicy.EXPONENTIAL, Duration.ofSeconds(10)).
2. Use runAttemptCount in doWork(): if attempts are below the threshold, return Result.retry(), otherwise Result.failure().
3. Configure backoff strategy: linear for frequent small uploads, exponential for rare large ones.

What is included in background upload implementation?

Our experience and guarantees

Our team has over 10 years of experience in mobile development and has implemented over 50 projects with background upload. For a social media app with 20 MB average uploads, we implemented iOS background URLSession and Android WorkManager with Foreground Service. Result: 99.8% upload completion rate even with frequent app backgrounding. We guarantee that your app will handle background upload correctly even with unstable connections. Native implementation via URLSession background configuration is 10 times more reliable than using standard URLSession in the background, and guarantees upload completion even if the app is killed.

Timelines: basic background upload—from 1 week. Complete solution with chunking, retry logic, and notifications—from 2 to 3 weeks. Contact us to evaluate your project—we will prepare a proposal within 1-2 days. Order a turnkey background upload implementation.