How is data exchanged between a client application and a server?

Data exchange between a client application and a server usually occurs through network requests via the HTTP or HTTPS protocol. The client sends a request (GET, POST, PUT, DELETE, etc.) to the server, which processes it and returns a response. The data format is most often JSON or XML.

In iOS, URLSession is often used for this purpose, allowing you to create and send requests, as well as receive and process responses.

Example of a simple GET request using URLSession:

let url = URL(string: "https://api.example.com/data")!
let task = URLSession.shared.dataTask(with: url) { data, response, error in
    guard let data = data, error == nil else {
        print("Error: \(error?.localizedDescription ?? "no data")")
        return
    }
    // Parse JSON
    if let json = try? JSONSerialization.jsonObject(with: data, options: []) {
        print("Received data: \(json)")
    }
}
task.resume()

Thus, the client and server exchange data through network requests and responses, using standardized formats and protocols.