server.accept() func always return nil

[ims-tech]

static func testServer() {

    DispatchQueue.global(qos: .background).async {

            let server = TCPServer(address: "127.0.0.1", port: 2442)
            switch server.listen() {
            case .success:
                    while true {
                        if let client = server.accept() {
                            self.echoService(client: client)
                        } else {
                            print("accept error")
                        }
                    }
            case .failure(let error):
                print(error)

            }
    }
}

static func echoService(client: TCPClient) { print("Newclient from:(client.address)[(client.port)]") let d = client.read(3) client.send(data: d!) client.close() }