Too many open files using NWListener on macOS - swift

Question

I'm trying to create an app that listens for incoming data on a UDP port using NWListener. This works fine until 248 messages are received - at which point the app crashes with the error message nw_listener_inbox_accept_udp socket() failed [24: Too many open files].
This (I think) relates to the file descriptor limit and so I tried resetting the NWListener within a safe count of 100, but the problem still persists. This seems clumsy and I'm not sure it's actually possible within a receive.
How can I truly reset it such that it releases any open files?
Full code below, which is instantiated within a SwiftUI content view using:
.onAppear() {
udpListener.start(port: self.udpPort)
}
Full class:
import Foundation
import Network
class UdpListener: NSObject, ObservableObject {
private var listener: NWListener?
private var port: NWEndpoint.Port?
#Published var incoming: String = ""
#Published var messageCount: Int = 0
func start(port: NWEndpoint.Port) {
self.port = port
do {
let params = NWParameters.udp
params.allowLocalEndpointReuse = true
self.listener = try NWListener(using: params, on: port)
self.listener?.stateUpdateHandler = {(newState) in
switch newState {
case .ready:
print("ready")
default:
break
}
}
self.listener?.newConnectionHandler = {(newConnection) in
newConnection.stateUpdateHandler = {newState in
switch newState {
case .ready:
self.receive(on: newConnection)
default:
break
}
}
newConnection.start(queue: DispatchQueue(label: "new client"))
}
} catch {
print("unable to create listener")
}
self.listener?.start(queue: .main)
}
func receive(on connection: NWConnection) {
connection.receiveMessage { (data, context, isComplete, error) in
if let error = error {
print(error)
return
}
guard let data = data, !data.isEmpty else {
print("unable to receive data")
return
}
let date = Date()
let formatter = DateFormatter()
formatter.dateFormat = "HH:mm:ss.SSSS"
DispatchQueue.main.async {
self.messageCount = self.messageCount + 1
self.incoming = formatter.string(from: date) + " " + String(decoding: data, as: UTF8.self) + "\n" + self.incoming
}
if self.messageCount == 100 {
print("Resetting")
self.listener?.stateUpdateHandler = nil
self.listener?.newConnectionHandler = nil
self.listener?.cancel()
self.listener = nil
self.start(port: self.port!)
}
}
}
}