How to work with UDP sockets in iOS, swift?

Question

I'm trying connect to local esp8266 UDP server. SwiftSocket haven't documentation. CocoaAsyncSocket doesn't work. How to connect and send data to udp server? What i should do?

I wrote sample UDP python server and tried connect to them via SwiftSocket and CocoaAsyncSocket. I'm don't get feedback from app. Server don't receive connections. For example- one of the most attempts:

    var connection = NWConnection(host: "255.255.255.255", port: 9093, using: .udp)

    connection.stateUpdateHandler = { (newState) in
        switch (newState) {
        case .ready:
            print("ready")
        case .setup:
            print("setup")
        case .cancelled:
            print("cancelled")
        case .preparing:
            print("Preparing")
        default:
            print("waiting or failed")
            break
        }
    }
    connection.start(queue: .global())
    connection.send(content: "Xyu".data(using: String.Encoding.utf8), completion: NWConnection.SendCompletion.contentProcessed(({ (NWError) in
        print(NWError)
    })))
    connection.receiveMessage { (data, context, isComplete, error) in
        print("Got it")
        print(data)
    }

Can't connect to the server

Answer 1

You need to wait until your connection is in the ready state before you try and send or receive any data. You will also need to hold a strong reference to your connection in a property to prevent it from being released as soon as the function exits.

var connection: NWConnection?

func someFunc() {

    self.connection = NWConnection(host: "255.255.255.255", port: 9093, using: .udp)

    self.connection?.stateUpdateHandler = { (newState) in
        switch (newState) {
        case .ready:
            print("ready")
            self.send()
            self.receive()
        case .setup:
            print("setup")
        case .cancelled:
            print("cancelled")
        case .preparing:
            print("Preparing")
        default:
            print("waiting or failed")

        }
    }
    self.connection?.start(queue: .global())

}

func send() {
    self.connection?.send(content: "Test message".data(using: String.Encoding.utf8), completion: NWConnection.SendCompletion.contentProcessed(({ (NWError) in
        print(NWError)
    })))
}

func receive() {
    self.connection?.receiveMessage { (data, context, isComplete, error) in
        print("Got it")
        print(data)
    }
}

Answer 2

This solution work for me! Thanks @Paulw11
Swift 4, XCode 10.1, iOS 12.0
Simple connect to the public UDP server (This is NOT optimal version but works):

import UIKit
import Network

class ViewController: UIViewController {

    var connection: NWConnection?
    var hostUDP: NWEndpoint.Host = "iperf.volia.net"
    var portUDP: NWEndpoint.Port = 5201

    override func viewDidLoad() {
        super.viewDidLoad()

        // Hack to wait until everything is set up
        var x = 0
        while(x<1000000000) {
            x+=1
        }
        connectToUDP(hostUDP,portUDP)
    }

    func connectToUDP(_ hostUDP: NWEndpoint.Host, _ portUDP: NWEndpoint.Port) {
        // Transmited message:
        let messageToUDP = "Test message"

        self.connection = NWConnection(host: hostUDP, port: portUDP, using: .udp)

        self.connection?.stateUpdateHandler = { (newState) in
            print("This is stateUpdateHandler:")
            switch (newState) {
                case .ready:
                    print("State: Ready\n")
                    self.sendUDP(messageToUDP)
                    self.receiveUDP()
                case .setup:
                    print("State: Setup\n")
                case .cancelled:
                    print("State: Cancelled\n")
                case .preparing:
                    print("State: Preparing\n")
                default:
                    print("ERROR! State not defined!\n")
            }
        }

        self.connection?.start(queue: .global())
    }

    func sendUDP(_ content: Data) {
        self.connection?.send(content: content, completion: NWConnection.SendCompletion.contentProcessed(({ (NWError) in
            if (NWError == nil) {
                print("Data was sent to UDP")
            } else {
                print("ERROR! Error when data (Type: Data) sending. NWError: \n \(NWError!)")
            }
        })))
    }

    func sendUDP(_ content: String) {
        let contentToSendUDP = content.data(using: String.Encoding.utf8)
        self.connection?.send(content: contentToSendUDP, completion: NWConnection.SendCompletion.contentProcessed(({ (NWError) in
            if (NWError == nil) {
                print("Data was sent to UDP")
            } else {
                print("ERROR! Error when data (Type: Data) sending. NWError: \n \(NWError!)")
            }
        })))
    }

    func receiveUDP() {
        self.connection?.receiveMessage { (data, context, isComplete, error) in
            if (isComplete) {
                print("Receive is complete")
                if (data != nil) {
                    let backToString = String(decoding: data!, as: UTF8.self)
                    print("Received message: \(backToString)")
                } else {
                    print("Data == nil")
                }
            }
        }
    }
}