Senior iOS Developer
Khaled joined Airmee through Toptal as his first contract on the premium freelance platform, tasked with solving a critical business problem: couriers inside buildings could not complete deliveries due to lack of network connectivity. He designed and implemented a sophisticated offline-first architecture that allowed the iOS courier app to function completely without network access, including photo capture, QR code scanning, and full delivery workflows. The solution ran at the operating system level, surviving phone locks and app backgrounding, with intelligent sync mechanisms that maintained data integrity when connectivity resumed.
Why I Joined
First Toptal contract opportunity - a milestone that validated the ability to work with premium international clients through competitive freelance platforms
- •Architected a complete offline-first system that enabled couriers to capture photos, scan QR codes, and complete delivery workflows without any network connectivity
- •Designed and implemented a hybrid storage system combining SQLite, CoreData, and NSCache for optimal data persistence across different use cases
- •Built an OS-level background service with heartbeat monitoring that continued operating even when the phone was locked or the app was backgrounded
- •Engineered a sophisticated sync queue with chronological ordering, server validation, and comprehensive fallback handling for duplicates and invalid data
- •Delivered a pure client-side solution requiring zero backend modifications, minimizing coordination complexity and deployment risk
- ✓Delivered a complete offline-first system in just 6 weeks, enabling couriers to complete deliveries inside buildings where network connectivity was impossible
- ✓Engineered an OS-level background service that maintained 100% operation continuity even when phones were locked or apps were backgrounded
- ✓Implemented a pure client-side solution requiring zero backend changes, reducing deployment complexity and eliminating server-side coordination requirements
- ✓Built a sophisticated sync mechanism with chronological queue management and full fallback handling that ensured zero data loss across offline-to-online transitions
Technology Stack
Situation
Airmee, a Swedish door-to-door delivery company, faced a critical operational problem: their couriers frequently entered buildings where mobile network coverage was nonexistent. Without connectivity, they could not take delivery photos, scan QR codes, or mark deliveries as complete. This caused delays, customer complaints, and operational inefficiencies that threatened the reliability of their service.
Task
Khaled was brought in as a Toptal contractor to solve this problem by adding offline capability to the existing iOS courier app. The solution needed to allow full delivery workflows without network, persist data safely, and sync everything reliably when connectivity resumed - all without requiring any backend changes.
Action
He redesigned the app's flow architecture to operate completely offline, implementing a hybrid storage system using SQLite for persistent offline data, CoreData for object graph management, and NSCache for temporary media. He built an OS-level background service using BGTaskScheduler with heartbeat monitoring that continued running even when the phone was locked. The sync system maintained chronological ordering to preserve delivery sequences and included comprehensive validation - manual checks, server checks, and a full fallback system for handling duplicates, invalid data, and redundant entries. The entire solution was implemented client-side, requiring no backend modifications.
Result
The project was delivered in just 6 weeks, fully solving the offline delivery problem. Couriers could now enter buildings with confidence, complete all delivery workflows without network, and have everything sync automatically when they emerged. The solution's elegance - zero backend changes required - minimized deployment risk and demonstrated advanced iOS architecture expertise. This first Toptal contract validated Khaled's ability to deliver for premium international clients.
Size: 1 people
Structure: Solo contractor working remotely with Airmee's internal engineering team
Reported to: Engineering Lead
0Skills Gained
Skills Deepened
- 💡Complex backend problems can often be solved elegantly on the client side without requiring server modifications
- 💡iOS provides powerful background execution capabilities when properly leveraged with BGTaskScheduler and heartbeat patterns
- 💡Data integrity across offline-to-online state transitions requires careful chronological ordering and comprehensive fallback strategies
- 💡Toptal provides access to premium international clients and validates engineering capability on the global stage