Cyril Chandelier

In iOS 13, Apple introduced Low Data Mode, an option users can enable on a per network basis to nicely ask the system and developers to consume as little data as possible.

It’s then the developer responsibility to conform to this preference. This option is easy to implement when using URLSession, but there is also a way to observe the status of the current network path, and the changes that may occur while your application or your screen is active using the Network framework:

import Network

let monitor = NWPathMonitor()
monitor.pathUpdateHandler = { path in
    if path.isConstrained {
        // Current network is constrained by user preference, aka iOS 13+ Low Data Mode
    } else if path.isExpensive {
        // Current network is considered expensive (eg: cellular, hotspot)
    } else {
        // Current network hasn't anything special, most likely is WiFi
    }
}
monitor.start(queue: DispatchQueue.global(qos: .background))

(Swift 5.1 / iOS 13.1)