iOS Networking: Handling Large Payloads

Large network requests—such as file uploads, bulk data syncs, or streaming APIs—can quickly overwhelm mobile devices if not managed carefully. In iOS, poor handling of these requests leads to memory pressure, failed retries, frozen UI, or even app crashes. Let’s walk through advanced strategies to handle large payloads efficiently.

 

1. Use Background URLSession for Uploads/Downloads

For tasks that may take minutes or need to continue when the app goes to background, always use URLSessionConfiguration.background. This hands control to the OS for scheduling and completion, which ensures reliability: Call this from your view using task {} in SwiftUI, which executes when the view appears:

let config = URLSessionConfiguration.background(withIdentifier: "com.myapp.largeUpload")
let session = URLSession(configuration: config, delegate: self, delegateQueue: nil)

Handle progress via URLSessionTaskDelegate and use didFinishEvents(forBackgroundURLSession:) to reconnect uploads on app relaunch.

2. Stream Data Instead of Loading Entire Payloads

Avoid loading large responses (e.g. 50MB JSON or videos) entirely into memory. Use URLSessionStreamTask or third-party stream parsers like InputStream and Codable in chunks:

 

let stream = InputStream(url: fileURL)!
stream.open()
var buffer = [UInt8](repeating: 0, count: 4096)
while stream.hasBytesAvailable {
    let read = stream.read(&buffer, maxLength: buffer.count)
    // Process chunk
}

This significantly reduces memory spikes and allows continuous processing.

3. Compress and Chunk Large Payloads

Before sending large data, compress it using gzip or zlib, and split it into smaller chunks. Implement resumable uploads using byte ranges or checkpoints. Some cloud APIs (e.g., Firebase, AWS S3) support chunked transfer encoding natively.

var request = URLRequest(url: uploadURL)
request.setValue("gzip", forHTTPHeaderField: "Content-Encoding")
// Send compressed data

4. Retry Intelligently with Exponential Backoff

Use exponential backoff with jitter for retries to avoid hammering the network during high load or instability:

 

func exponentialDelay(forAttempt attempt: Int) -> TimeInterval {
    let base = pow(2.0, Double(attempt))
    let jitter = Double.random(in: 0...0.5)
    return min(base + jitter, 60) // Max 60 seconds
}

Combine this with network reachability detection to pause/resume intelligently.

 

5. Use BackgroundTasks for Long-Running Sync

On iOS 13+, use BGProcessingTaskRequest to schedule large sync jobs in the background while the device is charging or on Wi-Fi:

 

let request = BGProcessingTaskRequest(identifier: "com.myapp.largeSync")
request.requiresNetworkConnectivity = true
request.requiresExternalPower = true
try? BGTaskScheduler.shared.submit(request)

Managing large network requests is about balancing performance, reliability, and user experience. Done right, your app can handle large syncs and file operations like a pro—without freezing, failing, or draining battery.