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

Solution 1

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")
                }
            }
        }
    }
}

Solution 2

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)
    }
}

Comments

[SBlincov]

Thank you for answer! When i'm run this code on empty project (run someFunction() from viewDidLoad() ) i get this error:

[SBlincov]

2019-02-12 22:28:41.553015+0300 Nanopix Pilot[3891:189405] [] nw_socket_service_writes_block_invoke [C1:1] sendmsg(fd 5, 3 bytes) [13: Permission denied]

[Paulw11]

You are trying to send a broadcast packet; I am not sure if this is permitted. It would be better to send a packet to the specific host you are trying to communicate with

[SBlincov]

Thank you so much! I successfully connected to public UDP server. Below i write final code

[user3069232]

Trying to get this to work on swift 5.x iOS 13. Sends data no problem, but I cannot seem to get it to receive anything. I am trying to use a python script to send a simple message.

[Flo]

You saved my life ! Finally I was able to open a connection and to send a message to the server using Swift 5 and without to upgrade my macOS to Catalina ! Thank you ! P.S.: If you need to connect using TCP is also working this example, just change from UDP to TCP.

[Ramcharan Reddy]

how to make the connection to listen for continuously?