Flutter JSON-RPC通信插件json_rpc_2的使用

json_rpc_2 是一个实现了 JSON-RPC 2.0 规范的Dart库。它使得在Flutter应用程序中实现客户端-服务器架构变得简单，特别是在需要通过WebSocket进行实时通信时。

安装

首先，在你的 pubspec.yaml 文件中添加依赖：

dependencies:
  json_rpc_2: ^3.0.0
  web_socket_channel: ^2.0.0

然后运行 flutter pub get 来安装这些包。

示例项目

下面是一个完整的示例项目，展示了如何创建一个JSON-RPC服务器和客户端，并通过WebSocket进行通信。

服务器端代码

服务器端代码创建了一个HTTP服务器，监听本地4321端口，并处理来自客户端的请求。每个连接都被转换为WebSocket连接，然后注册一些方法供客户端调用。

import 'dart:io';

import 'package:json_rpc_2/json_rpc_2.dart';
import 'package:web_socket_channel/io.dart';
import 'package:web_socket_channel/web_socket_channel.dart';

void main() async {
  var httpServer = await HttpServer.bind(InternetAddress.loopbackIPv4, 4321);
  print('Listening on ws://${httpServer.address.address}:${httpServer.port}');
  
  var connectedChannels =
      httpServer.transform(WebSocketTransformer()).map(IOWebSocketChannel.new);
  connectedChannels.listen(handleClient);
}

void handleClient(WebSocketChannel socket) {
  // The socket is a `StreamChannel<dynamic>` because it might emit binary
  // `List<int>`, but JSON RPC 2 only works with Strings so we assert it only
  // emits those by casting it.
  var server = Server(socket.cast<String>());

  // Any string may be used as a method name. JSON-RPC 2.0 methods are
  // case-sensitive.
  var i = 0;
  server.registerMethod('count', () {
    return i++;
  });

  // Methods can take parameters. They're presented as a `Parameters` object
  // which makes it easy to validate that the expected parameters exist.
  server.registerMethod('echo', (Parameters params) {
    return params['message'].value;
  });

  // `Parameters` has methods for verifying argument types.
  server.registerMethod('subtract', (Parameters params) {
    return params['minuend'].asNum - params['subtrahend'].asNum;
  });

  // [Parameters] also supports optional arguments.
  server.registerMethod('sort', (Parameters params) {
    var list = params['list'].asList;
    list.sort();
    if (params['descending'].asBoolOr(false)) {
      return list.reversed.toList();
    } else {
      return list;
    }
  });

  // A method can send an error response by throwing a `RpcException`.
  const divideByZero = 1;
  server.registerMethod('divide', (Parameters params) {
    var divisor = params['divisor'].asNum;
    if (divisor == 0) {
      throw RpcException(divideByZero, 'Cannot divide by zero.');
    }

    return params['dividend'].asNum / divisor;
  });

  // To give you time to register all your methods, the server won't start
  // listening for requests until you call `listen`. Messages are buffered until
  // listen is called. The returned Future won't complete until the connection
  // is closed.
  server.listen();
}

客户端代码

客户端代码连接到服务器并调用服务器上定义的方法。它演示了如何发送带参数的请求、处理响应以及捕获错误。

import 'package:json_rpc_2/json_rpc_2.dart';
import 'package:pedantic/pedantic.dart';
import 'package:web_socket_channel/web_socket_channel.dart';

void main() async {
  var socket = WebSocketChannel.connect(Uri.parse('ws://localhost:4321'));
  var client = Client(socket.cast<String>());

  // The client won't subscribe to the input stream until you call `listen`.
  unawaited(client.listen());

  try {
    // This calls the "count" method on the server. A Future is returned that
    // will complete to the value contained in the server's response.
    var count = await client.sendRequest('count');
    print('Count is $count');

    // Parameters are passed as a simple Map or, for positional parameters, an
    // Iterable. Make sure they're JSON-serializable!
    var echo = await client.sendRequest('echo', {'message': 'hello'});
    print('Echo says "$echo"!');

    // A notification is a way to call a method that tells the server that no
    // result is expected. Its return type is `void`; even if it causes an
    // error, you won't hear back.
    client.sendNotification('count');

    // If the server sends an error response, the returned Future will complete
    // with an RpcException. You can catch this error and inspect its error
    // code, message, and any data that the server sent along with it.
    try {
      await client.sendRequest('divide', {'dividend': 2, 'divisor': 0});
    } on RpcException catch (error) {
      print('RPC error ${error.code}: ${error.message}');
    }

    // Call sort method with descending order
    var sortedList = await client.sendRequest('sort', {'list': [3, 1, 2], 'descending': true});
    print('Sorted list: $sortedList');
  } finally {
    await client.close();
  }
}

总结

以上代码展示了如何在Flutter应用中使用 json_rpc_2 插件来实现JSON-RPC通信。通过WebSocket连接，你可以轻松地构建出高效的客户端-服务器交互模型。希望这个例子能帮助你更好地理解和使用 json_rpc_2 插件！如果你有任何问题或需要进一步的帮助，请随时提问。