• Consumer 消費者
• Producer 生産者
• Request-Response 請求-響應

在 MassTransit 中，一個消費者可以消費一種或多種消息

消費者的類型包括：普通消費者，saga，saga 狀态機，路由活動（分布式追蹤），處理器 handlers，工作消費者 job comsumers

• Consumer
• Instance
• Handler
• Others

public class Program { public static async Task Main() { var busControl = Bus.Factory.CreateUsingRabbitMq(cfg => { cfg.ReceiveEndpoint("order-service", e => { e.Consumer<SubmitOrderConsumer>(); }); }); } }

繼承 IConsumer，實現 Consume 方法

class SubmitOrderConsumer : IConsumer<SubmitOrder> { public async Task Consume(ConsumeContext<SubmitOrder> context) { await context.Publish<OrderSubmitted>(new { context.Message.OrderId }); } }

三個原則：

• 擁抱 The Hollywood Principle, which states, "Dont't call us, we'll call you."
• Consume 方法是一個被等待的方法，在執行中時其他消費者無法接收到這個消息，當這個方法完成的時候，消息被 ack，并且從隊列中移除
• Task 方法異常會導緻消息觸發 retry，如果沒有配置重試，消息将被投遞到失敗隊列

public class Program { public static async Task Main() { var submitOrderConsumer = new SubmitOrderConsumer(); var busControl = Bus.Factory.CreateUsingRabbitMq(cfg => { cfg.ReceiveEndpoint("order-service", e => { e.Instance(submitOrderConsumer); }); }); } }

所有接收到的消息都由一個消費者來實例來處理（請确保這個消費者類是線程安全）

Consumer 每次接收到消息都會 new 一個實例

public class Program { public static async Task Main() { var busControl = Bus.Factory.CreateUsingRabbitMq(cfg => { cfg.ReceiveEndpoint("order-service", e => { e.Handler<SubmitOrder>(async context => { await Console.Out.WriteLineAsync($"Submit Order Received: {context.Message.OrderId}"); }); }); }); } }

通過一個委托 Lambda 方法，來消費消息

• Saga<>
• StateMachineSaga<>

消息的生産可以通過兩種方式産生：發送和發布

發送的時候需要指定一個具體的地址 DestinationAddress，發布的時候消息會被廣播給所有訂閱了這個消息類型的消費者

基于這兩種規則，消息被定義為：命令 command 和事件 event

• send
• publish

可以調用以下對象的 send 方法來發送 command：

• ConsumeContext （在 Consumer 的 Consumer 方法參數中傳遞）
• ISendEndpointProvider（可以從 DI 中獲取）
• IBusControl（最頂層的控制對象，用來啟動和停止 masstransit 的控制器）

public class SubmitOrderConsumer : IConsumer<SubmitOrder> { private readonly IOrderSubmitter _orderSubmitter; public SubmitOrderConsumer(IOrderSubmitter submitter) => _orderSubmitter = submitter; public async Task Consume(IConsumeContext<SubmitOrder> context) { await _orderSubmitter.Process(context.Message); await context.Send(new StartDelivery(context.Message.OrderId, DateTime.UtcNow)); } }

public async Task SendOrder(ISendEndpointProvider sendEndpointProvider) { var endpoint = await sendEndpointProvider.GetSendEndpoint(_serviceAddress); await endpoint.Send(new SubmitOrder { OrderId = "123" }); }

• 發送地址
• 短地址
• Convention Map

• rabbitmq://localhost/input-queue
• rabbitmq://localhost/input-queue?durable=false

• GetSendEndpoint(new Uri("queue:input-queue"))

在配置文件中指定 map 規則

EndpointConvention.Map<StartDelivery>(new Uri(ConfigurationManager.AppSettings["deliveryServiceQueue"]));

直接發送

public class SubmitOrderConsumer : IConsumer<SubmitOrder> { private readonly IOrderSubmitter _orderSubmitter; public SubmitOrderConsumer(IOrderSubmitter submitter) => _orderSubmitter = submitter; public async Task Consume(IConsumeContext<SubmitOrder> context) { await _orderSubmitter.Process(context.Message); await context.Send(new StartDelivery(context.Message.OrderId, DateTime.UtcNow)); } }

可以調用以下對象的 publish 方法來發送 event：

• ConsumeContext （在 Consumer 的 Consumer 方法參數中傳遞）
• IPublishEndpoint（可以從 DI 中獲取）
• IBusControl（最頂層的控制對象，用來啟動和停止 masstransit 的控制器）

IPublishEndpoint

public async Task NotifyOrderSubmitted(IPublishEndpoint publishEndpoint) { await publishEndpoint.Publish<OrderSubmitted>(new { OrderId = "27", OrderDate = DateTime.UtcNow, }); }

Request-Response 模式讓應用程序之間解耦之後，依然采用同步的方式

• Consumer
• IClientFactory
• IRequestClient
• Send a request

public async Task Consume(ConsumeContext<CheckOrderStatus> context) { var order = await _orderRepository.Get(context.Message.OrderId); if (order == null) throw new InvalidOperationException("Order not found"); await context.RespondAsync<OrderStatusResult>(new { OrderId = order.Id, order.Timestamp, order.StatusCode, order.StatusText }); }

需要處理返回類型 OrderStatusResult，異步方式模拟同步，實際上同樣有消息隊列，消費者處理過程

public interface IClientFactory { IRequestClient<T> CreateRequestClient<T>(ConsumeContext context, Uri destinationAddress, RequestTimeout timeout); IRequestClient<T> CreateRequestClient<T>(Uri destinationAddress, RequestTimeout timeout); RequestHandle<T> CreateRequest<T>(T request, Uri destinationAddress, CancellationToken cancellationToken, RequestTimeout timeout); RequestHandle<T> CreateRequest<T>(ConsumeContext context, T request, Uri destinationAddress, CancellationToken cancellationToken, RequestTimeout timeout); }

通過 IBusControl 的 CreateClientFactory 方法可以得到 ClientFactory

public interface IRequestClient<TRequest> where TRequest : class { RequestHandle<TRequest> Create(TRequest request, CancellationToken cancellationToken, RequestTimeout timeout); Task<Response<T>> GetResponse<T>(TRequest request, CancellationToken cancellationToken, RequestTimeout timeout); }

RequestClient 可以創建請求，或者直接獲得響應

var serviceAddress = new Uri("rabbitmq://localhost/check-order-status"); var client = bus.CreateRequestClient<CheckOrderStatus>(serviceAddress); var response = await client.GetResponse<OrderStatusResult>(new { OrderId = id});