Swift Network Programming: From Sockets to WebSocket

Swift Network Programming: From Simple to Complex

When you first open Xcode and see an empty project, it seems like the real magic of network interaction is still far away. But believe me: Swift network programming is not rocket science, but a very tangible tool that turns a local application into part of the global internet. Today we will break down how to make your application "talk" to servers, exchange data, and do it beautifully.

I will show you not just dry definitions, but real-life scenarios from an iOS developer's experience. You will learn how Swift networking works at a low level (sockets) and at a high level (URLSession). And at the end — a bonus: how to connect WebSocket for a live chat. Let's go!

Understanding the Basics: How Networks Work in the Swift World

Before writing code, let's understand the concepts. Swift network programming is based on the same principles as in any other language: client-server architecture, TCP/UDP protocols, IP addresses, and ports. But there is a nuance — the Apple ecosystem offers its own frameworks that make a developer's life easier.

Key Technologies for Working with Networks in Swift

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• URLSession — the main tool for HTTP/HTTPS requests. Works with REST API, file downloads, background tasks.
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• Network.framework — low-level access to sockets, TCP/UDP. Introduced in iOS 12, replaced the old CFNetwork.
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• WebSocket (URLSessionWebSocketTask) — for real-time bidirectional communication.
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• CFStream — an old but still active way to work with data streams.
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Personally, I recommend starting with URLSession — it's like driving a car with an automatic transmission. And when you want "manual" — switch to Network.framework.

URLSession: Your Best Friend in Swift Network Programming

Let's start with the most popular tool. URLSession Swift is a powerful framework for sending and receiving data over the network. It supports caching, authentication, background downloads, and much more.

Basic GET Request

Imagine your application needs to display a list of users from a server. Here's how it's done:

import Foundation\n\n// 1. Create a URL\nguard let url = URL(string: "https://jsonplaceholder.typicode.com/users") else {\n    fatalError("Invalid URL")\n}\n\n// 2. Create a task\nlet task = URLSession.shared.dataTask(with: url) { data, response, error in\n    // 3. Handle errors\n    if let error = error {\n        print("Error: \\(error.localizedDescription)")\n        return\n    }\n    \n    // 4. Check the server response\n    guard let httpResponse = response as? HTTPURLResponse,\n          (200...299).contains(httpResponse.statusCode) else {\n        print("Invalid status code")\n        return\n    }\n    \n    // 5. Work with data\n    if let data = data {\n        do {\n            let users = try JSONDecoder().decode([User].self, from: data)\n            print("Received \\(users.count) users")\n        } catch {\n            print("Parsing error: \\(error)")\n        }\n    }\n}\n\n// 6. Start the task\ntask.resume()

Note: task.resume() is mandatory! Otherwise, the request will never execute. This is a common mistake for beginners in Swift network programming.

POST Request with Body

Now let's send data to the server:

func createUser(name: String, email: String) {\n    guard let url = URL(string: "https://jsonplaceholder.typicode.com/users") else {\n        return\n    }\n    \n    var request = URLRequest(url: url)\n    request.httpMethod = "POST"\n    request.setValue("application/json", forHTTPHeaderField: "Content-Type")\n    \n    let body