How can I attach a header to all published messages? - masstransit

Question

I have a particular header that I'd like to attach to all messages that I publish. I can attach this header on a case-by-case basis by specifying it in the Publish call:
_bus.Publish(myMessage, context => context.SetHeader("my key", "my value"));
This works fine but it becomes a chore to maintain this SetHeader call for every publish. Is there a way, during bus configuration or anywhere else, to specify a header that will be attached to all messages? That is, is there a way to do something like the following?
ServiceBusFactory.New(sbc =>
{
sbc.UseRabbitMq();
sbc.ReceiveFrom(hdoQueue);
// This is what I'd like to be able to do:
sbc.BeforePublish(context => context.SetHeader("my key", "my value"));
});
I believe there is a solution that involves implementing IOutboundMessageInterceptor but I can't find a way to attach my interceptor. There is a ServiceBusConfigurator.AddInboundInterceptor method but not a ServiceBusConfigurator.AddOutboundInterceptor method.

Answer 1

My intuition was correct, I was able to do what I wanted by implementing IOutboundMessageInterceptor:
public class AttachHeadersOutboundInterceptor : IOutboundMessageInterceptor
{
public void PreDispatch(ISendContext context)
{
context.SetHeader("my key", "my value");
}
public void PostDispatch(ISendContext context)
{
}
}
Oddly there is no ServiceBusConfigurator.AddOutboundInterceptor method, so I just created one (by copying the code for AddInboundInterceptor from github):
public static class MassTransitExtensions
{
public static void AddOutboundInterceptor(this ServiceBusConfigurator configurator,
IOutboundMessageInterceptor interceptor)
{
var builderConfigurator = new PostCreateBusBuilderConfigurator(bus =>
{
var interceptorConfigurator = new OutboundMessageInterceptorConfigurator(bus.OutboundPipeline);
interceptorConfigurator.Create(interceptor);
});
configurator.AddBusConfigurator(builderConfigurator);
}
}
And then I attach it during bus configuration:
ServiceBusFactory.New(sbc =>
{
sbc.UseRabbitMq();
sbc.ReceiveFrom(hdoQueue);
sbc.AddOutboundInterceptor(new AttachHeadersOutboundInterceptor());
});
Problem solved.