MassTransit–Adding a header using middleware

MassTransit offers a lot of flexibility and it is easy to tweak it to your needs.

With all this power it is not always easy to find out what is the best way to solve a specific problem. I wanted to include a header with information about the user in every message.

I solved it by adding two filters; one for sending messages and one for publishing messages:

	public class PublishUserHeaderFilter<T> : IFilter<PublishContext<T>> where T : class
	{
	private readonly IUserFactory _userFactory;
	public PublishUserHeaderFilter(IUserFactory userFactory)
	{
	_userFactory = userFactory;
	}
	public void Probe(ProbeContext context)
	{
	context.CreateFilterScope("publishuserheader");
	}
	public Task Send(PublishContext<T> context, IPipe<PublishContext<T>> next)
	{
	context.Headers.Set("user", _userFactory.GetCurrentUser());
	return next.Send(context);
	}
	}

view raw PublishUserHeaderFilter.cs hosted with ❤ by GitHub

	public class SendUserHeaderFilter<T> : IFilter<SendContext<T>> where T : class
	{
	private readonly IUserFactory _userFactory;
	public SendUserHeaderFilter(IUserFactory userFactory)
	{
	_userFactory = userFactory;
	}
	public void Probe(ProbeContext context)
	{
	context.CreateFilterScope("senduserheader");
	}
	public Task Send(SendContext<T> context, IPipe<SendContext<T>> next)
	{
	context.Headers.Set("user", _userFactory.GetCurrentUser());
	return next.Send(context);
	}
	}

view raw SendUserHeaderFilter.cs hosted with ❤ by GitHub

Inside these filters I resolved an IUserFactory which gave me access to the underlying user. This is how I implemented this in ASP.NET Core:

	public class HttpContextUserFactory : IUserFactory
	{
	private readonly IHttpContextAccessor _httpContextAccessor;
	public HttpContextUserFactory(IHttpContextAccessor httpContextAccessor)
	{
	_httpContextAccessor = httpContextAccessor;
	}
	public IUser GetCurrentUser()
	{
	var httpUser = _httpContextAccessor?.HttpContext?.User;
	if (httpUser == null)
	return new UnknownUser();
	return new WebUser(httpUser);
	}
	}

view raw HttpContextUserFactory.cs hosted with ❤ by GitHub

	public interface IUserFactory
	{
	IUser GetCurrentUser();
	}

view raw IUserFactory.cs hosted with ❤ by GitHub

I registered both filters in the IoC container(Autofac in our case) to make sure that the dependencies are correctly resolved:

	var container=new ContainerBuilder();
	container.RegisterGeneric(typeof(SendUserHeaderFilter<>)).InstancePerLifetimeScope();
	container.RegisterGeneric(typeof(PublishUserHeaderFilter<>)).InstancePerLifetimeScope();

view raw ContainerConfig.cs hosted with ❤ by GitHub

And as a last step I configured MassTransit to use these filters:

	container.AddMassTransit(config =>
	{
	//Removed the other config settings
	config.UsingRabbitMq((context, cfg) =>
	{
	cfg.UsePublishFilter(typeof(PublishUserHeaderFilter<>), context);
	cfg.UseSendFilter(typeof(SendUserHeaderFilter<>), context);
	}
	}

view raw MassTransitConfig.cs hosted with ❤ by GitHub