MassTransit3 how to make request from consumer

问题:

I want to make a req/res request from IConsumer.Consume() method, but I don't see any method on ConsumeContext<> that returns a reference to IRequestClient<,>. Do I need to hold a reference to IBusControl somewhere and use it or I can use context somehow?

回答1:

In this case, it is best to create the request client outside of the consumer and pass it as a dependency to the consumer as an IRequestClient<,> interface. The request client is created with IBus, which is outside of the consumer context.

It also ensures that the request will be less likely to deadlock with the broker because responses are received on the bus endpoint, and not the receive endpoint of the consumer (which, if you had a concurrency limit of 1, would never finish).

It's also not possible to connect consumers to a started receive endpoint, which is a requirement of the request/response handling (it happens under the covers). The bus, however, can connect consumers for messages which are sent (responses are sent to the bus address, versus being published) which is why it is used for responses to the requests.

To keep message tracking continuous, it may be nice to set the InitiatorId on the outbound request to the CorrelationId of the consumer message, as well as copying the ConversationId. This helps with tracing and keeping track of the overall message command/event flow.