RawDatagramSocket 类 抽象 接口

UDP套接字的非缓冲接口。

原始数据报套接字按照底层操作系统接收的数据块顺序，传递Stream中的RawSocketEvent。

注意，不会收到RawSocketEvent.readClosed事件，因为UDP套接字不能由远程端关闭。

它与POSIX原始套接字不同。

import 'dart:io';
import 'dart:typed_data';

void main() async {
  // Read the current time from an NTP server.
  final serverAddress = (await InternetAddress.lookup('pool.ntp.org')).first;
  final clientSocket = await RawDatagramSocket.bind(
      serverAddress.type == InternetAddressType.IPv6
          ? InternetAddress.anyIPv6
          : InternetAddress.anyIPv4,
      0);
  final ntpQuery = Uint8List(48);
  ntpQuery[0] = 0x23; // See RFC 5905 7.3

  clientSocket.listen((event) {
    switch (event) {
      case RawSocketEvent.read:
        final datagram = clientSocket.receive();
        // Parse `datagram.data`
        clientSocket.close();
        break;
      case RawSocketEvent.write:
        if (clientSocket.send(ntpQuery, serverAddress, 123) > 0) {
          clientSocket.writeEventsEnabled = false;
        }
        break;
      case RawSocketEvent.closed:
        break;
      default:
        throw "Unexpected event $event";
    }
  });
}