ios-background.md•5.01 kB
# iOS Background Processing Guide
## Overview
This guide covers implementing Lightning Network synchronization in iOS background tasks using LDK.
## Background Task Types
### 1. Background Refresh
```swift
import BackgroundTasks
import LightningDevKit
class LightningBackgroundHandler {
static let taskIdentifier = "com.example.lightning.sync"
func scheduleBackgroundSync() {
let request = BGAppRefreshTaskRequest(identifier: Self.taskIdentifier)
request.earliestBeginDate = Date(timeIntervalSinceNow: 15 * 60) // 15 minutes
do {
try BGTaskScheduler.shared.submit(request)
} catch {
print("Failed to schedule background task: \(error)")
}
}
func handleBackgroundTask(_ task: BGAppRefreshTask) {
task.expirationHandler = {
// Clean up if task expires
task.setTaskCompleted(success: false)
}
Task {
do {
// Sync Lightning node
await syncLightningNode()
// Schedule next sync
scheduleBackgroundSync()
task.setTaskCompleted(success: true)
} catch {
task.setTaskCompleted(success: false)
}
}
}
}
```
### 2. Background Processing
```swift
func handleLongRunningSync(_ task: BGProcessingTask) {
let syncOperation = BlockingQueue<Result<Void, Error>>()
Task {
do {
// Perform full chain sync
try await performFullChainSync()
// Update channel states
try await updateAllChannels()
// Process pending events
try await processLightningEvents()
syncOperation.append(.success(()))
} catch {
syncOperation.append(.failure(error))
}
}
// Wait for completion or expiration
if let result = syncOperation.getWithTimeout(timeout: 25) {
switch result {
case .success:
task.setTaskCompleted(success: true)
case .failure:
task.setTaskCompleted(success: false)
}
}
}
```
## Network Graph Sync
### Using Rapid Gossip Sync
```swift
class BackgroundNetworkGraphSync {
let networkGraph: Bindings.NetworkGraph
let rapidGossipSync: Bindings.RapidGossipSync
func syncInBackground() async throws {
// Download latest gossip data
let gossipUrl = URL(string: "https://rapidsync.lightningdevkit.org/snapshot/")!
let (data, _) = try await URLSession.shared.data(from: gossipUrl)
// Update network graph
let result = rapidGossipSync.updateNetworkGraphNoStd(
updateData: [UInt8](data),
currentTimeUnix: UInt64(Date().timeIntervalSince1970)
)
guard result.isOk() else {
throw LightningError.gossipSyncFailed
}
}
}
```
## Best Practices
### 1. Efficient Data Usage
- Use compact block filters for chain sync
- Implement incremental gossip updates
- Cache network graph between sessions
### 2. Battery Optimization
- Schedule syncs during device charging
- Batch multiple operations together
- Use appropriate background task types
### 3. Error Handling
```swift
enum BackgroundSyncError: Error {
case networkUnavailable
case syncTimeout
case insufficientTime
case chainSyncFailed
}
func handleBackgroundErrors(_ error: Error) {
switch error {
case BackgroundSyncError.networkUnavailable:
// Reschedule for later
scheduleDelayedSync()
case BackgroundSyncError.syncTimeout:
// Save partial progress
savePartialSyncState()
default:
// Log for debugging
Logger.shared.error("Background sync failed: \(error)")
}
}
```
## Testing Background Tasks
### Debug Commands
```swift
// Force immediate background refresh (debug only)
#if DEBUG
e -l objc -- (void)[[BGTaskScheduler sharedScheduler] _simulateLaunchForTaskWithIdentifier:@"com.example.lightning.sync"]
#endif
```
### Monitoring
```swift
class BackgroundSyncMonitor {
func logSyncMetrics() {
let metrics = [
"last_sync": lastSyncDate,
"sync_duration": syncDuration,
"blocks_synced": blocksSynced,
"channels_updated": channelsUpdated
]
Analytics.log("background_sync_completed", metrics)
}
}
```
## Common Issues
### 1. Task Not Running
- Ensure Info.plist contains BGTaskSchedulerPermittedIdentifiers
- App must have been launched at least once
- Device must have sufficient battery
### 2. Sync Timeout
- Break large syncs into smaller chunks
- Use checkpoints to resume from last position
- Implement progressive backoff for retries
### 3. Memory Pressure
- Release unnecessary objects during sync
- Use autorelease pools for batch operations
- Monitor memory usage with Instruments