.NET 雲原生架構師訓練營（子產品二 基礎鞏固 RabbitMQ Masstransit 詳解）--學習筆記

2.6.7 RabbitMQ -- Masstransit 詳解

• 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，實作 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執行個體來處理（請確定這個消費者類是線程安全）

Consumer 每次接收到消息都會 new 一個執行個體

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：發送和釋出

發送的時候需要指定一個具體的位址 DestinationAddress，釋出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：指令 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 中擷取）
• IBusControl（最頂層的控制對象，用來啟動和停止 masstransit 的控制器）

ConsumeContext

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));
    }
}      

ISendEndpointProvider

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

• 發送位址
• 短位址
• Convention Map

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

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

在配置檔案中指定 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：

• IPublishEndpoint（可以從 DI 中擷取）

IPublishEndpoint

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

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

• 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
    });
}      

需要處理傳回類型 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 可以建立請求，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});