Hybrid REST + WebSocket control for remote hardware

Energy / EV

Industry: Energy / EV

Platform: iOS

Stack: Swift · Combine · URLSession WebSocket · CoreData

Description: iOS client controlling remote hardware over hybrid REST + WebSocket with offline-safe schedules.

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The engineering surface was a two-channel IoT control client: REST as the transactional authority for discrete commands, a persistent WebSocket as the high-frequency telemetry channel, and a local persistence layer for schedules that must execute regardless of phone or hardware connectivity. Connection-state visualization had to be a first-class UI surface, not an afterthought, because the hardware sits on flaky cellular and the user's question is always the same: is the session still going. Authority hierarchy between the two channels eliminates an entire category of UI race conditions.

We owned the iOS client, the channel reconciliation rules, the offline-capable schedule store, and the connection-state surface. The client owned the cloud backend, the device firmware, and the customer messaging tooling.

Engagement: ~5-month build · single iOS specialist · 2022.

Engineering signal: schedules executed correctly on hardware through multi-hour cloud outages via device-local authoritative cache.