ios - NWNetworking/NWListener如何正确接收UDP广播报文？

Question

当通过 UDP 接收直接消息时，我可以正常运行以下代码:

import UIKit
import Network

class ViewController: UIViewController {

    var udpListener:NWListener?
    var backgroundQueueUdpListener   = DispatchQueue(label: "udp-lis.bg.queue", attributes: [])
    var backgroundQueueUdpConnection = DispatchQueue(label: "udp-con.bg.queue", attributes: [])
            
    var connections = [NWConnection]()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        myOnButton(self)
    }
    
    @IBAction func myOnButton(_ sender: Any) {
        
        guard self.udpListener == nil else {
            print(" 🧨 Already listening. Not starting again")
            return
        }
        
        do {
            self.udpListener = try NWListener(using: .udp, on: 2000)
            self.udpListener?.stateUpdateHandler = { (listenerState) in
                
                switch listenerState {
                case .setup:
                    print("Listener: Setup")
                case .waiting(let error):
                    print("Listener: Waiting \(error)")
                case .ready:
                    print("Listener: Ready and listens on port: \(self.udpListener?.port?.debugDescription ?? "-")")
                case .failed(let error):
                    print("Listener: Failed \(error)")
                case .cancelled:
                    print("Listener: Cancelled by myOffButton")
                    for connection in self.connections {
                        connection.cancel()
                    }
                    self.udpListener = nil
                default:
                    break;
                }
            }
            
            self.udpListener?.start(queue: backgroundQueueUdpListener)
            self.udpListener?.newConnectionHandler = { (incomingUdpConnection) in

                print ("💁 New connection \(incomingUdpConnection.debugDescription)")
                
                incomingUdpConnection.stateUpdateHandler = { (udpConnectionState) in
                    switch udpConnectionState {
                    case .setup:
                        print("Connection: setup")
                    case .waiting(let error):
                        print("Connection: waiting: \(error)")
                    case .ready:
                        print("Connection: ready")
                        self.connections.append(incomingUdpConnection)
                        self.processData(incomingUdpConnection)
                    case .failed(let error):
                        print("Connection: failed: \(error)")
                        self.connections.removeAll(where: {incomingUdpConnection === $0})
                    case .cancelled:
                        print("Connection: cancelled")
                        self.connections.removeAll(where: {incomingUdpConnection === $0})
                    default:
                        break
                    }
                }

                incomingUdpConnection.start(queue: self.backgroundQueueUdpConnection)
            }
            
        } catch {
            print("🧨")
        }
        
    }
    @IBAction func myOffButton(_ sender: Any) {
        udpListener?.cancel()
    }
  
    func processData(_ incomingUdpConnection :NWConnection) {
        
        incomingUdpConnection.receiveMessage(completion: {(data, context, isComplete, error) in
            
            if let data = data, !data.isEmpty {
                if let string = String(data: data, encoding: .ascii) {
                    print ("DATA       = \(string)")
                }
            }

            if error == nil {
                self.processData(incomingUdpConnection)
            }
        })
        
    }
   
}

像这样直接向设备发送无穷无尽的 UDP 包:

echo -n "Testdata" | socat - udp-datagram:192.168.2.126:2000,broadcast,sourceport=2000

按预期工作，所有消息都到达:

Listener: Waiting POSIXErrorCode: Network is down
Listener: Ready and listens on port: 2000
💁 New connection [C1 192.168.2.134:2000 udp, local: 192.168.2.126:2000, indefinite, server, path satisfied (Path is satisfied), interface: en0, scoped, ipv4, ipv6, dns]
Connection: ready
DATA       = Testdata
DATA       = Testdata
DATA       = Testdata
DATA       = Testdata
...

但尝试对广播消息进行同样的操作

echo -n "Testat" | socat - udp-datagram:255.255.255.255:2000,broadcast,sourceport=2000

导致仅接收第一条消息，并与每个接收到的 UDP 数据包建立新连接。

Listener: Waiting POSIXErrorCode: Network is down
Listener: Ready and listens on port: 2000
💁 New connection [C1 192.168.2.134:2000 udp, local: 0.0.0.0:2000, indefinite, server, path satisfied (Path is satisfied), interface: en0, ipv4, ipv6, dns]
Connection: ready
DATA       = Testdata
2020-06-28 14:22:03.668116+0200 networking[25440:13489733] [] nw_channel_reclassify_input reclassify failed, could not find client for slot 77926755-A281-4AFD-9649-92FBD1A21FA6
💁 New connection [C2 192.168.2.134:2000 udp, local: 0.0.0.0:2000, indefinite, server, path satisfied (Path is satisfied), interface: en0, ipv4, ipv6, dns]
2020-06-28 14:22:04.384443+0200 networking[25440:13489733] [] nw_channel_reclassify_input reclassify failed, could not find client for slot 7EAC98FA-F665-43C1-9B15-B68B74A56BBC
💁 New connection [C3 192.168.2.134:2000 udp, local: 0.0.0.0:2000, indefinite, server, path satisfied (Path is satisfied), interface: en0, ipv4, ipv6, dns]
2020-06-28 14:22:05.096808+0200 networking[25440:13489733] [] nw_channel_reclassify_input reclassify failed, could not find client for slot AA3EE3BA-D891-4D07-87AF-0CB0A9382CDF
💁 New connection [C4 192.168.2.134:2000 udp, local: 0.0.0.0:2000, indefinite, server, path satisfied (Path is satisfied), interface: en0, ipv4, ipv6, dns]
2020-06-28 14:22:05.714651+0200 networking[25440:13489733] [] nw_channel_reclassify_input reclassify failed, could not find client for slot ED108E8B-E9BC-43C3-8AA7-B4BD0515EB54

解决方法是在每次收到数据包后取消连接，但我怀疑这是用于接收 UDP 广播消息的方式。那么死循环接收UDP广播包的正确做法是什么？

Answer 1

好的，我得到了某种答案。

我在 Objective-C 中遇到了同样的基本问题。我采取了取消处理程序中的连接的步骤，这种方法可行，但您最终会丢失数据 - 根据我的经验，大约 30% - 因为流无法获取广播数据。

不过，我确实从 dts 那里得到了反馈，基本上是这样的——网络库不是为接收广播 UDP 而设计的。

我已经恢复到 BSD 套接字。