前言

上一节咱们讲了LocalEventBus，本节来讲本地事件总线（DistributedEventBus），采用的RabbitMQ进行实现。

Volo.Abp.EventBus.RabbitMQ模块内部代码并不多，RabbitMQ的操作都集中在Volo.Abp.RabbitMQ这个包中。

正文

我们从模块定义开始看，项目启动的时候分别读取了appsetting.json的配置参数和调用了RabbitMqDistributedEventBus的Initialize函数。

    public class AbpEventBusRabbitMqModule : AbpModule
    {
        public override void ConfigureServices(ServiceConfigurationContext context)
        {
            var configuration = context.Services.GetConfiguration();

            Configure<AbpRabbitMqEventBusOptions>(configuration.GetSection("RabbitMQ:EventBus"));
        }

        public override void OnApplicationInitialization(ApplicationInitializationContext context)
        {
            context
                .ServiceProvider
                .GetRequiredService<RabbitMqDistributedEventBus>()
                .Initialize();
        }
    }

在Initialize函数中我们根据 MessageConsumerFactory.Create向内部进行查阅可以看到最终调用方法为RabbitMqMessageConsumer.TryCreateChannelAsync并且在其内部我们可以看到下面代码,这里定义了消费的回调函数。反推Initialize方法其实是在启动一个消费者。

      public void Initialize()
        {
            Consumer = MessageConsumerFactory.Create(
                new ExchangeDeclareConfiguration(
                    AbpRabbitMqEventBusOptions.ExchangeName,
                    type: "direct",
                    durable: true
                ),
                new QueueDeclareConfiguration(
                    AbpRabbitMqEventBusOptions.ClientName,
                    durable: true,
                    exclusive: false,
                    autoDelete: false
                ),
                AbpRabbitMqEventBusOptions.ConnectionName
            );

            Consumer.OnMessageReceived(ProcessEventAsync);

            SubscribeHandlers(AbpDistributedEventBusOptions.Handlers);
        }

 var consumer = new AsyncEventingBasicConsumer(Channel);
                consumer.Received += HandleIncomingMessageAsync;

继续向下看Consumer.OnMessageReceived(ProcessEventAsync);该方法向一个并发安全集合输入一个委托事件，并该事件会在上面的HandleIncomingMessageAsync会调中触发故确定为消费者的执行逻辑，而ProcessEventAsync其实还是走了我们在讲LocalEventBus哪一套，寻找Handler执行函数。

SubscribeHandlers还是上节讲的基类的函数，这里要注意内部调用的Subscribe该方法中的 Consumer.BindAsync会根据为消费者Bind路由，这样才能触发事件处理函数。

       public override IDisposable Subscribe(Type eventType, IEventHandlerFactory factory)
        {
            var handlerFactories = GetOrCreateHandlerFactories(eventType);

            if (factory.IsInFactories(handlerFactories))
            {
                return NullDisposable.Instance;
            }

            handlerFactories.Add(factory);

            if (handlerFactories.Count == 1) //TODO: Multi-threading!
            {
                Consumer.BindAsync(EventNameAttribute.GetNameOrDefault(eventType));
            }

            return new EventHandlerFactoryUnregistrar(this, eventType, factory);
        }

看完了事件消费者我们来看看事件发布，直接看PublishAsync函数就完事了，整个函数非常简单，都是RabbitMQ的操作语法，这里的路由Key是在EventNameAttribute.GetNameOrDefault(eventType);函数中通过读取ETO上指定注解Name来指定的。

protected Task PublishAsync(
            string eventName,
            byte[] body,
            IBasicProperties properties,
            Dictionary<string, object> headersArguments = null,
            Guid? eventId = null)
        {
            using (var channel = ConnectionPool.Get(AbpRabbitMqEventBusOptions.ConnectionName).CreateModel())
            {
                channel.ExchangeDeclare(
                    AbpRabbitMqEventBusOptions.ExchangeName,
                    "direct",
                    durable: true
                );

                if (properties == null)
                {
                    properties = channel.CreateBasicProperties();
                    properties.DeliveryMode = RabbitMqConsts.DeliveryModes.Persistent;
                }

                if (properties.MessageId.IsNullOrEmpty())
                {
                    properties.MessageId = (eventId ?? GuidGenerator.Create()).ToString("N");
                }

                SetEventMessageHeaders(properties, headersArguments);

                channel.BasicPublish(
                    exchange: AbpRabbitMqEventBusOptions.ExchangeName,
                    routingKey: eventName,
                    mandatory: true,
                    basicProperties: properties,
                    body: body
                );
            }

            return Task.CompletedTask;
        }

解析

整个分布式事件的实现其实非常简单，在事件发生时发布者只需要定义好路由名称和消息内容发送RabbitMQ中，而消费者则是在项目运行的时候的通过调用Initialize就启动起来了。

这里我们也同样根据整个原理自己实现一下这个流程。

在Dppt.EventBus分别定义IDistributedEventBus、DistributedEventBusOptions、IDistributedEventHandler分别用于采用分布式事件总线调用、配置选项用于存储处理程序Handler、定义分布式处理程序抽象。

新建Dppt.EventBus.RabbitMQ类库先简单对RabbitMQ进行一个简单的封装

public class RabbitMqConnections : IRabbitMqConnections
    {
        private readonly IConnectionFactory _connectionFactory;
        private readonly ILogger<RabbitMqConnections> _logger;
        IConnection _connection;
        bool _disposed;
        public RabbitMqConnections(IConnectionFactory connectionFactory, ILogger<RabbitMqConnections> logger)
        {
            _connectionFactory = connectionFactory;
            _logger = logger;
        }


        public bool IsConnected
        {
            get
            {
                return _connection != null && _connection.IsOpen && !_disposed;
            }
        }

        public void TryConnect() {

            _connection = _connectionFactory.CreateConnection();

        }


        public IModel CreateModel()
        {
            if (!IsConnected)
            {
                throw new InvalidOperationException("No RabbitMQ connections are available to perform this action");
            }

            return _connection.CreateModel();
        }


        public void Dispose()
        {
            if (_disposed) return;

            _disposed = true;

            try
            {
                _connection.Dispose();
            }
            catch (IOException ex)
            {
                _logger.LogCritical(ex.ToString());
            }
        }

    }

然后我们分别定义ExchangeDeclareConfiguration、QueueDeclareConfiguration用于记录配置信息。

开始处理RabbitMqEventBus处理程序首先是发布事件,大体代码如下就是往RabbitMQ里面丢消息。

        /// <summary>
        /// rabbmitmq 连接服务
        /// </summary>
        public readonly IRabbitMqConnections _rabbitMqConnections;


public Task PublishAsync<TEvent>(TEvent eventData)
        {
            var eventName = EventNameAttribute.GetNameOrDefault(typeof(TEvent));
            var body = JsonSerializer.Serialize(eventData);
            return PublishAsync(eventName, body, null, null);
        }

        public Task PublishAsync(string eventName, string body, IBasicProperties properties, Dictionary<string, object> headersArguments = null, Guid? eventId = null)
        {

            if (!_rabbitMqConnections.IsConnected)
            {
                _rabbitMqConnections.TryConnect();
            }
            using (var channel = _rabbitMqConnections.CreateModel())
            {
                // durable 设置队列持久化  
                channel.ExchangeDeclare(RabbitMqEventBusOptions.ExchangeName, "direct", durable: true);

                if (properties == null)
                {
                    properties = channel.CreateBasicProperties();
                    // 设置消息持久化
                    properties.DeliveryMode = 2;
                }

                if (properties.MessageId.IsNullOrEmpty())
                {
                    // 消息的唯一性标识
                    properties.MessageId = (eventId ?? Guid.NewGuid()).ToString("N");
                }

                SetEventMessageHeaders(properties, headersArguments);

                channel.BasicPublish(
                   exchange: RabbitMqEventBusOptions.ExchangeName,
                   routingKey: eventName,
                   mandatory: true,
                   basicProperties: properties,
                   body: Encoding.UTF8.GetBytes(body)
               );

            }

            return Task.CompletedTask;
        }

      private void SetEventMessageHeaders(IBasicProperties properties, Dictionary<string, object> headersArguments)
        {
            if (headersArguments == null)
            {
                return;
            }

            properties.Headers ??= new Dictionary<string, object>();

            foreach (var header in headersArguments)
            {
                properties.Headers[header.Key] = header.Value;
            }
        }

然后就是消费者的处理,我们同样定义Initialize函数，并简化部分封装代码，完成消费者启动。

 public void Initialize()
        {

            Exchange = new ExchangeDeclareConfiguration(RabbitMqEventBusOptions.ExchangeName,"direct",true);
            Queue = new QueueDeclareConfiguration(RabbitMqEventBusOptions.ClientName, true, false, false);

            // 启动一个消费者
            if (!_rabbitMqConnections.IsConnected)
            {
                _rabbitMqConnections.TryConnect();
            }

            try
            {

                Channel = _rabbitMqConnections.CreateModel();



                Channel.ExchangeDeclare(
                  exchange: Exchange.ExchangeName,
                  type: Exchange.Type,
                  durable: Exchange.Durable,
                  autoDelete: Exchange.AutoDelete,
                  arguments: Exchange.Arguments
              );


                Channel.QueueDeclare(
                   queue: Queue.QueueName,
                   durable: Queue.Durable,
                   exclusive: Queue.Exclusive,
                   autoDelete: Queue.AutoDelete,
                   arguments: Queue.Arguments
               );

                var consumer = new AsyncEventingBasicConsumer(Channel);
                consumer.Received += HandleIncomingMessageAsync;

                Channel.BasicConsume(
                    queue: Queue.QueueName,
                    autoAck: false,
                    consumer: consumer
                );

                SubscribeHandlers(DistributedEventBusOptions.Handlers);
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error:" + ex.Message);
            }
        }

参数配置这边主要是读取AppSetting信息和索要Handler

 public static class DpptEventBusRabbitMqRegistrar
    {
        public static void AddDpptEventBusRabbitMq(this IServiceCollection services, IConfiguration configuration, List<Type> types)
        {
     
            services.AddSingleton<IRabbitMqConnections>(sp =>
            {
                var logger = sp.GetRequiredService<ILogger<RabbitMqConnections>>();

                var factory = new ConnectionFactory()
                {
                    HostName = configuration["RabbitMQ:EventBusConnection"],
                    VirtualHost = configuration["RabbitMQ:EventBusVirtualHost"],
                    DispatchConsumersAsync = true,
                    AutomaticRecoveryEnabled = true
            };

                if (!string.IsNullOrEmpty(configuration["RabbitMQ:EventBusUserName"]))
                {
                    factory.UserName = configuration["RabbitMQ:EventBusUserName"];
                }

                if (!string.IsNullOrEmpty(configuration["RabbitMQ:EventBusPassword"]))
                {
                    factory.Password = configuration["RabbitMQ:EventBusPassword"];
                }

                return new RabbitMqConnections(factory, logger);
            });

            var distributedHandlers = types;
            foreach (var item in distributedHandlers)
            {
                services.AddSingleton(item);
            }

            services.Configure<DistributedEventBusOptions>(options =>
            {
                options.Handlers.AddIfNotContains(distributedHandlers);
            });

            services.Configure<DpptRabbitMqEventBusOptions>(options => {

                options.ExchangeName = configuration["RabbitMQ:EventBus:ExchangeName"];
                options.ClientName = configuration["RabbitMQ:EventBus:ClientName"];
            });

            services.AddSingleton<IDistributedEventBus, RabbitMqDistributedEventBus>();

          
        }
    }

测试

新建一个空项目，进行插件注册，然后创建ETO和Handler进行测试。

测试结果放在下面了。

结语

本次挑选了一个比较简单的示例来讲，整个EventBus我应该分成3篇 下一篇我来讲分布式事务。

最后欢迎各位读者关注我的博客， https://github.com/MrChuJiu/Dppt/tree/master/src 欢迎大家Star

另外这里有个社区地址(https://github.com/MrChuJiu/Dppt/discussions)，如果大家有技术点希望我提前档期可以写在这里，希望本项目助力我们一起成长