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Implement request/reply

Use request/reply when one component needs a direct response from another component, and you want that exchange over InterBus instead of an in-process call.

When to use request/reply vs publish/send​

  • Use request/reply for one-to-one interactions where the caller must await a typed response
  • Use publish for fan-out events where no direct response is expected
  • Use send for one-way point-to-point commands

1. Define request and reply contracts​

public sealed record GetOrderStatus(Guid OrderId);
public sealed record OrderStatusReply(Guid OrderId, string Status);

2. Register InterBus and the responder consumer​

IRequestClient<TRequest, TReply> is registered by InterBus as an open generic scoped service.

using InterBus.Extensions;
using InterBus.Generated;
using InterBus.InMemory.Extensions;

builder.Services.AddInterBus(bus =>
{
    bus.AddInMemoryTransport();
    bus.AddConsumer<GetOrderStatusConsumer>();
});

3. Reply from the consumer using context.ReplyTo​

The requester sets InterBusHeaders.ReplyTo automatically. In consumers, read it through IConsumeContext.ReplyTo and send the reply message to that address.

public sealed class GetOrderStatusConsumer(IPublisher publisher) : IConsumer<GetOrderStatus>
{
    public async Task Consume(
        GetOrderStatus message,
        IConsumeContext context,
        CancellationToken cancellationToken = default)
    {
        if (context.ReplyTo is null) return;

        var reply = new OrderStatusReply(message.OrderId, "Shipped");
        await publisher.SendAsync(context.ReplyTo, reply, cancellationToken);
    }
}

4. Send requests from application code​

Inject and use IRequestClient<TRequest, TReply> in a scoped service.

public sealed class OrderQueryService(
    IRequestClient<GetOrderStatus, OrderStatusReply> client)
{
    public Task<OrderStatusReply> GetStatusAsync(
        Guid orderId,
        CancellationToken cancellationToken = default)
    {
        return client.RequestAsync(new GetOrderStatus(orderId), cancellationToken);
    }
}

You can also attach request headers via the configure delegate:

var reply = await client.RequestAsync(
    new GetOrderStatus(orderId),
    ctx => ctx.Headers["x-trace-source"] = "orders-api",
    cancellationToken);

5. Apply cancellation/timeout at the caller​

Use a cancellation token (optionally with a timeout) to bound how long the caller waits for a reply.

using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
cts.CancelAfter(TimeSpan.FromSeconds(5));

var reply = await client.RequestAsync(new GetOrderStatus(orderId), cts.Token);

Behavior notes​

  • Request messages are published and include an automatically generated reply address
  • Transports typically create one temporary reply queue per running app instance and reuse it for request/reply exchanges to avoid per-request infrastructure churn
  • The request client waits for a reply of the expected TReply type
  • Non-matching reply message types are ignored by the temporary reply endpoint

For API-level details, see Request/reply reference.