/swift-networking

Connection State Handling

State Machine

setup -> preparing -> waiting <-> ready -> failed/cancelled

State Handling (iOS 12+)

connection.stateUpdateHandler = { [weak self] state in
    switch state {
    case .preparing:
        self?.updateUI(.connecting)
    case .waiting(let error):
        // DON'T fail here - framework retries when network returns
        self?.updateUI(.waiting)
    case .ready:
        self?.startCommunication()
    case .failed(let error):
        self?.showError(error)
    case .cancelled:
        self?.cleanup()
    @unknown default: break
    }
}

State Handling (iOS 26+)

Task {
    for await state in connection.states {
        switch state {
        case .preparing: print("Connecting...")
        case .waiting(let error): print("Waiting: \(error)")
        case .ready: await startCommunication()
        case .failed(let error): print("Failed: \(error)")
        case .cancelled: print("Cancelled")
        @unknown default: break
        }
    }
}

The Waiting State (Critical)

.waiting means network unavailable but framework retries automatically.

// WRONG - Poor UX
case .waiting:
    showError("Connection failed")

// CORRECT
case .waiting:
    showStatus("Waiting for network...")

Viability Updates

connection.viabilityUpdateHandler = { isViable in
    if !isViable {
        // Don't tear down! May recover when network returns
        showStatus("Connection interrupted...")
    }
}

Better Path Available

connection.betterPathUpdateHandler = { betterPathAvailable in
    if betterPathAvailable {
        migrateToNewConnection()
    }
}

Multipath TCP

let parameters = NWParameters.tcp
parameters.multipathServiceType = .handover  // Seamless WiFi/cellular transition

Common POSIX Errors

NWPathMonitor

let monitor = NWPathMonitor()
monitor.pathUpdateHandler = { path in
    if path.status == .satisfied {
        if path.usesInterfaceType(.wifi) { print("WiFi") }
        if path.isExpensive { print("Cellular/hotspot") }
    }
}
monitor.start(queue: .main)

Use for global UI updates, not pre-connection checks.