无法在颤动中打开 .pem 文件

Question

我是编程初学者，对于一个学校项目，我正在构建一个 android 应用程序来使用 esp 32 和 AWS IOT 打开/关闭 LED。我正在使用 mqtt_client 9.6.4，当我运行 aws_iot.dart 示例时，我能够连接到 AWS IOT 并使用相同的脚本执行操作。当我在颤振中使用相同的代码时，我在调试控制台中收到以下错误消息，E/flutter (15280): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: FileSystemException: Cannot open file, path = 'AmazonRootCA1.pem'（操作系统错误：没有这样的文件或目录，errno = 2）

如何解决？

import 'dart:async';
import 'dart:io';
import 'dart:typed_data';
import 'package:flutter/services.dart';

import 'lib/mqtt_server_client.dart';
import 'lib/mqtt_client.dart';
import 'package:pem/pem.dart';

var switch1 = 0;

Future<int> main() async {
  const url = 'xxxxxxxxxxxxxxxx.amazonaws.com';

  const port = 8883;

  const clientId = 'Flutter';

 
  final client = MqttServerClient.withPort(url, clientId, port);

 
  client.secure = true;

  client.keepAlivePeriod = 20;
  
  client.setProtocolV311();

  client.logging(on: true);

  final context = SecurityContext.defaultContext;

  context.setClientAuthorities('AmazonRootCA1.pem');

  context.useCertificateChain('certificate.pem.crt');

  context.usePrivateKey('private.pem.key');


  client.securityContext = context;

  final connMess =
      MqttConnectMessage().withClientIdentifier(clientId).startClean();
  client.connectionMessage = connMess;

  
  try {
    print('MQTT client connecting to AWS IoT....');
    await client.connect();
  } on Exception catch (e) {
    print('MQTT client exception - $e');
    client.disconnect();
  }

  if (client.connectionStatus!.state == MqttConnectionState.connected) {
    print('MQTT client connected to AWS IoT');

    
    const topic = 'esp32/relay1';
    const topic2 = 'esp32/relay2';
    final builder = MqttClientPayloadBuilder();
    builder.addString('{\"status\":\"0\"}');
    
    client.publishMessage(topic, MqttQos.atLeastOnce, builder.payload!);

    
    client.subscribe(topic2, MqttQos.atLeastOnce);
    
    client.updates!.listen((List<MqttReceivedMessage<MqttMessage>> c) {
      final recMess = c[0].payload as MqttPublishMessage;
      final pt =
          MqttPublishPayload.bytesToStringAsString(recMess.payload.message);
      print(
          'EXAMPLE::Change notification:: topic is <${c[0].topic}>, payload is <-- $pt -->');
      print('');
    });
  } else {
    print(
        'ERROR MQTT client connection failed - disconnecting, state is ${client.connectionStatus!.state}');
    client.disconnect();
  }

  print('Sleeping....');
  await MqttUtilities.asyncSleep(60);

  print('Disconnecting');
  client.disconnect();

  return 0;
}

Answer 1

我会尝试使用 SecurityContext 方法的 Bytes 变体。

首先，您需要确保您引用的文件在您的pubspec.yaml 文件中定义：

flutter:
  assets:
    - assets/AmazonRootCA1.pem # assuming you placed these files in a folder called assets
    - assets/certificate.pem.crt
    - assets/private.pem.key

这将确保文件与应用程序一起打包，以便您可以使用rootBundle 加载它们。

然后在您的代码中使用rootBundle 加载文件并将数据作为字节传递给SecurityContext。

  final context = SecurityContext.defaultContext;

  final clientAuthorities = await rootBundle.load('assets/AmazonRootCA1.pem');
  context.setClientAuthoritiesBytes(clientAuthorities.buffer.asUint8List());

  final certificateChain = await rootBundle.load('assets/certificate.pem.crt');
  context.useCertificateChainBytes(certificateChain.buffer.asUint8List());

  final privateKey = await rootBundle.load('assets/private.pem.key');
  context.usePrivateKeyBytes(privateKey.buffer.asUint8List());

顺便说一句，我有点困惑为什么你在颤振项目中的主要方法不调用runApp，而是返回int。但是如果你确实在flutter应用的main方法中使用了上面的代码，你可能需要在使用rootBundle.load之前调用main中的WidgetsFlutterBinding.ensureInitialized();。