無法在顫振中打開.pem檔案

我是編程初學者，對于一個學校專案，我正在構建一個 android 應用程式來使用 esp 32 和 AWS IOT 打開/關閉 LED。我使用的是 mqtt_client 9.6.4，當我運行 aws_iot.dart 示例時，我能夠連接到 AWS IOT 并使用相同的腳本執行操作。當我在 flutter 中使用相同的代碼時，我在除錯控制臺 E/flutter (15280) 中收到以下錯誤訊息：[ERROR:flutter/lib/ui/ui_dart_state.cc(209)] 未處理的例外：FileSystemException：無法打開檔案，路徑 = 'AmazonRootCA1.pem'（作業系統錯誤：沒有那個檔案或目錄，errno = 2）

如何解決這個問題？

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;
}

uj5u.com熱心網友回復：

我會嘗試使用這些SecurityContext方法的 Bytes 變體。

首先，您需要確保您參考的檔案在您的pubspec.yaml檔案中定義：

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

這將確保檔案與應用程式打包在一起，以便您可以使用rootBundle.

然后在您的代碼中使用加載檔案rootBundle并將資料傳遞給SecurityContext位元組。

  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());

順便說一句，我對為什么 Flutter 專案中的 main 方法不呼叫runApp，而是回傳一個int. 但是，如果您確實在 Flutter 應用程式的 main 方法中使用了上面的代碼，則可能需要WidgetsFlutterBinding.ensureInitialized();在main使用rootBundle.load.

標籤：扑 镖 aws-iot aws-iot-core

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