All of the Nugets are named WolverineFx.* even though the libraries and namespaces are all Wolverine.*. Wolverine was well underway when I found out someone is squatting on the name “Wolverine” in Nuget, and that’s why there’s a discrepancy in the naming.
As of today, Wolverine is officially at 1.0 and available on Nuget! As far as I am concerned, this absolutely means that Wolverine is ready for production usage, the public APIs should be considered to be stable, and the documentation is reasonably complete.
To answer the obvious question of “what is it?”, Wolverine is a set of libraries that can be used in .NET applications as an:
And when combined with Marten to form the full fledged “critter stack,” I’m hoping that it grows to become the singular best platform for CQRS with Event Sourcing on any development platform.
Wolverine is significantly different (I think) from existing tools in the .NET space in that it delivers a developer experience that results in much less ceremony and friction — and I think that’s vital to enable teams to better iterate and adapt their code over time in ways you can’t efficiently do in higher ceremony tools.
There are neither beginnings nor endings to the Wheel of Time. But it was a beginning.”
Robert Jordan
Now, software projects (and their accompanying documentation websites) are never complete, only abandoned. There’ll be bugs, holes in the current functionality, and feature requests as users hit usages and permutations that haven’t yet been considered in Wolverine. In the case of Wolverine, I have every intention of sticking with Wolverine and its sibling Marten project as Oskar, Babu, and I try to build a services/product model company of some sort around the tools.
And Wolverine 1.0.1 will surely follow soon as folks inevitably find issues with the initial version. Software projects like Wolverine are far more satisfying if you can think of them as a marathon and a continuous process.
The long meandering path here
My superpower compared to many of my peers is that I have a much longer attention span than most. It means that I have from time to time been the living breathing avatar of the sunk cost fallacy, but it’s also meant that Wolverine got to see the light of day.
To rewind a bit:
FubuMVC that was an alternative OSS web development framework that started in earnest around 2009 with the idea of being low ceremony with a strong middleware approach
Around 2013 I helped build a minimal service bus tool called FubuTransportation that basically exposed the FubuMVC runtime approach to asynchronous messaging
About 2015 after FubuMVC had clearly failed and what became known as .NET Core made .NET a *lot* more attractive again, I wrote some “vision” documents about what a next generation FubuMVC would look like on .NET Core that tried to learn from fubu’s technical and performance shortcomings
In late 2015, I helped build the very first version of Marten for internal usage at my then employer
In 2016 I started working in earnest on that reboot of FubuMVC and called it “Jasper,” but focused mostly on the service bus aspect of it
Jasper was released as 1.0 during the very worst of the pandemic in 2020 and was more or less abandoned by me and everyone else
Marten started gaining a lot of steam and took a big step forward in the giant 4.0 release in late 2021
Jasper was restarted in 2022 partially as a way to extend Marten into a full blown CQRS platform (don’t worry, both Marten & Wolverine are plenty useful by themselves)
And finally a 1.0 in June 2023 after the reboot inevitably took longer than I’d hoped
A whole lot of gratitude and thanks
Wolverine has been ingesting a long time and descends from the earlier FubuMVC efforts, so there’s been a lot of folks who have contributed or helped guide the shape of Wolverine along the way. Here’s a very incomplete list:
Chad Myers and Josh Flanagan started FubuMVC way back when and some of the ideas about how to apply middleware and even some code has survived even until now
Josh Arnold was my partner with FubuMVC for a long time
Corey Kaylor was part of the core FubuMVC team, wrote FubuTransportation with me, and was part of getting Marten off the ground
Oskar and Babu have worked with me on the Marten team for years, and they took the brunt of Marten support and the recent 6.0 release while I was focused on Wolverine
Khalid Abuhakmeh has helped quite a bit with both Marten & Wolverine strategy over the years and contributed all of the graphics for the projects
My previous boss Denys Grozenok did a lot to test early Wolverine, encouraged the work, and contributed quite a few ideas around usability
Eric J. Smith made some significant suggestions that streamlined the API usability of Wolverine
And quite a few other folks who have contributed code fixes, extensions, or taken the time to write bug reproductions that go a long ways toward making a project like Wolverine better.
For folks that have followed me for awhile, I’m back with yet another alternative, HTTP web service framework with Wolverine.Http — but I swear that I learned a whole slew of lessons from FubuMVC‘s failure a decade ago. Wolverine.Http shown here is very much a citizen within the greater ASP.Net Core ecosystem and happily interoperates with a great deal of Minimal API and the rest of ASP.Net Core.
For folks who have no idea what a “fubu” is, Wolverine’s HTTP add on shown here is potentially a way to build more efficient web services in .NET with much less boilerplate and noise code than the equivalent functionality in ASP.Net Core MVC or Minimal API. And especially less code ceremony and indirection than you get with the usage of any kind of mediator tooling in conjunction with MVC or Minimal API.
Server side applications are frequently built with some mixture of HTTP web services, asynchronous processing, and asynchronous messaging. Wolverine by itself can help you with the asynchronous processing through its local queue functionality, and it certainly covers all common asynchronous messaging requirements.
For a simplistic example, let’s say that we’re inevitably building a “Todo” application where we want a web service endpoint that allows our application to create a new Todo entity, save it to a database, and raise an TodoCreated event that will be handled later and off to the side by Wolverine.
Even in this simple example usage, that endpoint should be developed such that the creation of the new Todo entity and the corresponding TodoCreated event message either succeed or fail together to avoid putting the system into an inconsistent state. That’s a perfect use case for Wolverine’s transactional outbox. While the Wolverine team believes that Wolverine’s outbox functionality is significantly easier to use outside of the context of message handlers than other .NET messaging tools, it’s still easiest to use within the context of a message handler, so let’s just build out a Wolverine message handler for the CreateTodo command:
public class CreateTodoHandler
{
public static (Todo, TodoCreated) Handle(CreateTodo command, IDocumentSession session)
{
var todo = new Todo { Name = command.Name };
// Just telling Marten that there's a new entity to persist,
// but I'm assuming that the transactional middleware in Wolverine is
// handling the asynchronous persistence outside of this handler
session.Store(todo);
return (todo, new TodoCreated(todo.Id));
}
}
Okay, but we still need to expose a web service endpoint for this functionality. We could utilize Wolverine within an MVC controller as a “mediator” tool like so:
public class TodoController : ControllerBase
{
[HttpPost("/todoitems")]
[ProducesResponseType(201, Type = typeof(Todo))]
public async Task<ActionResult> Post(
[FromBody] CreateTodo command,
[FromServices] IMessageBus bus)
{
// Delegate to Wolverine and capture the response
// returned from the handler
var todo = await bus.InvokeAsync<Todo>(command);
return Created($"/todoitems/{todo.Id}", todo);
}
}
Or we could do the same thing with Minimal API:
// app in this case is a WebApplication object
app.MapPost("/todoitems", async (CreateTodo command, IMessageBus bus) =>
{
var todo = await bus.InvokeAsync<Todo>(command);
return Results.Created($"/todoitems/{todo.Id}", todo);
}).Produces<Todo>(201);
While the code above is certainly functional, and many teams are succeeding today using a similar strategy with older tools like MediatR, the Wolverine team thinks there are some areas to improve in the code above:
When you look into the internals of the runtime, there’s some potentially unnecessary performance overhead as every single call to that web service does service locations and dictionary lookups that could be eliminated
There’s some opportunity to reduce object allocations on each request — and that can be a big deal for performance and scalability
It’s not that bad, but there’s some boilerplate code above that serves no purpose at runtime but helps in the generation of OpenAPI documentation through Swashbuckle
At this point, let’s look at some tooling in the WolverineFx.Http Nuget library that can help you incorporate Wolverine into ASP.Net Core applications in a potentially more successful way than trying to “just” use Wolverine as a mediator tool.
After adding the WolverineFx.Http Nuget to our Todo web service, I could use this option for a little bit more efficient delegation to the underlying Wolverine message handler:
// This is *almost* an equivalent, but you'd get a status
// code of 200 instead of 201. If you care about that anyway.
app.MapPostToWolverine<CreateTodo, Todo>("/todoitems");
The code up above is very close to a functional equivalent to our early Minimal API or MVC Controller usage, but there’s a couple differences:
In this case the HTTP endpoint will return a status code of 200 instead of the slightly more correct 201 that denotes a creation. Most of use aren’t really going to care, but we’ll come back to this a little later
In the call to MapPostToWolverine(), Wolverine.HTTP is able to make a couple performance optimizations that completely eliminates any usage of the application’s IoC container at runtime and bypasses some dictionary lookups and object allocation that would have to occur in the simple “mediator” approach
I personally find the indirection of delegating to a mediator tool to add more code ceremony and indirection than I prefer, but many folks like that approach because of how bloated MVC Controller types can become in enterprise systems over time. What if instead we just had a much cleaner way to code an HTTP endpoint that still helped us out with OpenAPI documentation?
That’s where the Wolverine.Http “endpoint” model comes into play. Let’s take the same Todo creation endpoint and use Wolverine to build an HTTP endpoint:
// Introducing this special type just for the http response
// gives us back the 201 status code
public record TodoCreationResponse(int Id)
: CreationResponse("/todoitems/" + Id);
// The "Endpoint" suffix is meaningful, but you could use
// any name if you don't mind adding extra attributes or a marker interface
// for discovery
public static class TodoCreationEndpoint
{
[WolverinePost("/todoitems")]
public static (TodoCreationResponse, TodoCreated) Post(CreateTodo command, IDocumentSession session)
{
var todo = new Todo { Name = command.Name };
// Just telling Marten that there's a new entity to persist,
// but I'm assuming that the transactional middleware in Wolverine is
// handling the asynchronous persistence outside of this handler
session.Store(todo);
// By Wolverine.Http conventions, the first "return value" is always
// assumed to be the Http response, and any subsequent values are
// handled independently
return (
new TodoCreationResponse(todo.Id),
new TodoCreated(todo.Id)
);
}
}
The code above will actually generate the exact same OpenAPI documentation as the MVC Controller or Minimal API samples earlier in this post, but there’s significantly less boilerplate code needed to expose that information. Instead, Wolverine.Http relies on type signatures to “know” what the OpenAPI metadata for an endpoint should be. In conjunction with Wolverine’s Marten integration (or Wolverine’s EF Core integration too!), you potentially get a very low ceremony approach to writing HTTP services that also utilizes Wolverine’s durable outbox without giving up anything in regards to crafting effective and accurate OpenAPI metadata about your services.
Marten 6.0 came out last week. Rather than describe that, just take a look at Oskar’s killer release notes write up on GitHub for V6. This also includes some updates to the Marten documentation website. Oskar led the charge on this release, so big thanks are due to him — in no small part by allowing me to focus on Wolverine by taking the brunt of the “Critter Stack” Discord rooms. The healthiness of the Marten community shows up with a slew of new contributors in this release.
With Marten 6.0 out, it’s on to finally getting to Wolverine 1.0:
Wolverine has lingered for way, way too long for my taste in a pre-1.0 status, but it’s getting closer. A couple weeks ago I felt like Wolverine 1.0 was very close as soon as the documentation was updated, but then I kept hearing repeated feedback about how early adopters want or need first class database multi-tenancy support as part of their Wolverine + Marten experience — and lesser number wanting some sort of EF Core + Wolverine multi-tenancy, but I’m going to put that aside just for now.
Cool, so I started jotting down what first class support for multi-tenancy through multiple databases was going to entail:
Some way to communicate the message tenant information through to Wolverine with message metadata. Easy money, that didn’t take much.
A little bit of change to the Marten transactional middleware in Wolverine to be tenant aware. Cool, that’s pretty small. Especially after a last minute change I made in Marten 6.0 specifically to support Wolverine.
Uh, oh, the durable inbox/outbox support in Wolverine will require specific table storage in every single tenant database, and you’d probably also want an “any tenant” master database as well for transactions that aren’t for a specific tenant. Right off the bat, this is much more complex than the other bullet points above. Wolverine could try to stretch its current “durability agent” strategy for multiple databases, but it’s a little too greedy on database connection usage and I was getting some feedback from potential users who were concerned by exactly that issue. At that point, I thought it would be helpful to reduce the connection usage, which…
Led me to wanting an approach where only one running node was processing the inbox/outbox recovery instead of each node hammering the database with advisory locks to figure out if anything needed to be recovered from previous nodes that shut down before finishing their work. Which now led me to wanting…
Some kind of leadership election in Wolverine, which now means that Wolverine needs durable storage for all the active nodes and the assignments to each node — which is functionality I wanted to build out soon regardless for Marten’s “async projection” scalability.
So to get the big leadership election, durability agent assignment across nodes, and finally back to the multi-tenancy support in Wolverine, I’ve got a bit of work to get through. It’s going well so far, but it’s time consuming because of the sheer number of details and the necessity of rigorously testing bitwise before trying to put it all together end to end.
There are a few other loose ends for Wolverine 1.0, but the work described up above is the main battle right now before Wolverine efforts shift to documentation and finally a formal 1.0 release. Famous last words of a fool, but I’m hoping to roll out Wolverine 1.0 right now during the NDC Oslo conference in a couple weeks.
For easier unit testing, it’s often valuable to separate responsibilities of “deciding” what to do from the actual “doing.” The side effect facility in Wolverine is an example of this strategy.You will need Wolverine 0.9.17 that just dropped for this feature.
At times, you may with to make Wolverine message handlers (or HTTP endpoints) be pure functions as a way of making the handler code itself easier to test or even just to understand. All the same, your application will almost certainly be interacting with the outside world of databases, file systems, and external infrastructure of all types. Not to worry though, Wolverine has some facility to allow you to declare the side effects as return values from your handler.
To make this concrete, let’s say that we’re building a message handler that will take in some textual content and an id, and then try to write that text to a file at a certain path. In our case, we want to be able to easily unit test the logic that “decides” what content and what file path a message should be written to without ever having any usage of the actual file system (which is notoriously irritating to use in tests).
First off, I’m going to create a new “side effect” type for writing a file like this:
// ISideEffect is a Wolverine marker interface
public class WriteFile : ISideEffect
{
public string Path { get; }
public string Contents { get; }
public WriteFile(string path, string contents)
{
Path = path;
Contents = contents;
}
// Wolverine will call this method.
public Task ExecuteAsync(PathSettings settings)
{
if (!Directory.Exists(settings.Directory))
{
Directory.CreateDirectory(settings.Directory);
}
return File.WriteAllTextAsync(Path, Contents);
}
}
And the matching message type, message handler, and a settings class for configuration:
// An options class
public class PathSettings
{
public string Directory { get; set; }
= Environment.CurrentDirectory.AppendPath("files");
}
public record RecordText(Guid Id, string Text);
public class RecordTextHandler
{
public WriteFile Handle(RecordText command)
{
return new WriteFile(command.Id + ".txt", command.Text);
}
}
At runtime, Wolverine is generating this code to handle the RecordText message:
public class RecordTextHandler597515455 : Wolverine.Runtime.Handlers.MessageHandler
{
public override System.Threading.Tasks.Task HandleAsync(Wolverine.Runtime.MessageContext context, System.Threading.CancellationToken cancellation)
{
var recordTextHandler = new CoreTests.Acceptance.RecordTextHandler();
var recordText = (CoreTests.Acceptance.RecordText)context.Envelope.Message;
var pathSettings = new CoreTests.Acceptance.PathSettings();
var outgoing1 = recordTextHandler.Handle(recordText);
// Placed by Wolverine's ISideEffect policy
return outgoing1.ExecuteAsync(pathSettings);
}
}
To explain what is happening up above, when Wolverine sees that any return value from a message handler implements the Wolverine.ISideEffect interface, Wolverine knows that that value should have a method named either Execute or ExecuteAsync() that should be executed instead of treating the return value as a cascaded message. The method discovery is completely by method name, and it’s perfectly legal to use arguments for any of the same types available to the actual message handler like:
Service dependencies from the application’s IoC container
The actual message
Any objects created by middleware
CancellationToken
Message metadata from Envelope
Taking this functionality farther, here’s a new example from the WolverineFx.Marten library that exploits this new side effect model to allow you to start event streams or store/insert/update documents from a side effect return value without having to directly touch Marten‘s IDocumentSession:
public static class StartStreamMessageHandler
{
// This message handler is creating a brand new Marten event stream
// of aggregate type NamedDocument. No services, no async junk,
// pure function mechanics. You could unit test the method by doing
// state based assertions on the StartStream object coming back out
public static StartStream Handle(StartStreamMessage message)
{
return MartenOps.StartStream<NamedDocument>(message.Id, new AEvent(), new BEvent());
}
public static StartStream Handle(StartStreamMessage2 message)
{
return MartenOps.StartStream<NamedDocument>(message.Id, new CEvent(), new BEvent());
}
}
As I get a little more time and maybe ambition, I want to start blogging more about how Wolverine is quite different from the “IHandler of T” model tools like MediatR, MassTransit, or NServiceBus. The “pure function” usage above potentially makes for a big benefit in terms of testability and longer term maintainability.
Today I’m going to continue with a contrived example from the “payment ingestion service,” this time on what I’m so far calling “compound handlers” in Wolverine. When building a system with any amount of business logic or workflow logic, there’s some philosophical choices that Wolverine is trying to make:
To maximize testability, business or workflow logic — as much as possible — should be in pure functions that are easily testable in isolated unit tests. In other words, you should be able to test this code without integration tests or mock objects. Just data in, and state-based assertions.
Of course your message handler will absolutely need to read data from our database in the course of actually handling messages. It’ll also need to write data to the underlying database. Yet we still want to push toward the pure function approach for all logic. To get there, I like Jim Shore’s A-Frame metaphor for how code should be organized to isolate business logic away from infrastructure and into nicely testable code.
I certainly didn’t set out this way years ago when what’s now Wolverine was first theorized, but Wolverine is trending toward using more functional decomposition with fewer abstractions rather than “traditional” class centric C# usage with lots of interfaces, constructor injection, and IoC usage. You’ll see what I mean when we hit the actual code
I don’t think that mock objects are evil per se, but they’re absolutely over-used in our industry. All I’m trying to suggest in this post is to structure code such that you don’t have to depend on stubs or any other kind of fake to set up test inputs to business or workflow logic code.
Consider the case of a message handler that needs to process a command message to apply a payment to principal within an existing loan. Depending on the amount and the account in question, the handler may need to raise domain events for early principle payment penalties (or alerts or whatever you actually do in this situation). That logic is going to need to know about both the related loan and account information in order to make that decision. The handler will also make changes to the loan to reflect the payment made as well, and commit those changes back to the database.
Just to sum things up, this message handler needs to:
Look up loan and account data
Use that data to carry out the business logic
Potentially persist the changed state
Alright, on to the handler, which I’m going to accomplish with a single class that uses two separate methods:
public record PayPrincipal(Guid LoanId, decimal Amount, DateOnly EffectiveDate);
public static class PayPrincipalHandler
{
// Wolverine will call this method first by naming convention.
// If you prefer being more explicit, you can use any name you like and decorate
// this with [Before]
public static async Task<(Account, LoanInformation)> LoadAsync(PayPrincipal command, IDocumentSession session,
CancellationToken cancellation)
{
Account? account = null;
var loan = await session
.Query<LoanInformation>()
.Include<Account>(x => x.AccountId, a => account = a)
.Where(x => x.Id == command.LoanId)
.FirstOrDefaultAsync(token: cancellation);
if (loan == null) throw new UnknownLoanException(command.LoanId);
if (account == null) throw new UnknownAccountException(loan.AccountId);
return (account, loan);
}
// This is the main handler, but it's able to use the data built
// up by the first method
public static IEnumerable<object> Handle(
// The command
PayPrincipal command,
// The information loaded from the LoadAsync() method above
LoanInformation loan,
Account account,
// We need this only to mark items as changed
IDocumentSession session)
{
// The next post will switch this to event sourcing I think
var status = loan.AcceptPrincipalPayment(command.Amount, command.EffectiveDate);
switch (status)
{
case PrincipalStatus.BehindSchedule:
// Maybe send an alert? Act on this in some other way?
yield return new PrincipalBehindSchedule(loan.Id);
break;
case PrincipalStatus.EarlyPayment:
if (!account.AllowsEarlyPayment)
{
// Maybe just a notification?
yield return new EarlyPrincipalPaymentDetected(loan.Id);
}
break;
}
// Mark the loan as being needing to be persisted
session.Store(loan);
}
}
Wolverine itself is weaving in the call first to LoadAsync(), and piping the results of that method to the inputs of the inner Handle() method, which now gets to be almost a pure function with just the call to IDocumentSession.Store() being “impure” — but at least that one single method is relatively painless to mock.
The point of doing this is really just to make the main Handle() method where the actual business logic is happening be very easily testable with unit tests as you can just push in the Account and Loan information. Especially in cases where there’s likely many permutations of inputs leading to different behaviors, it’s very advantageous to be able to walk right up to just the business rules and push inputs right into that, then do assertions on the messages returned from the Handle() function and/or assert on modifications to the Loan object.
TL:DR — Repository abstractions over persistence tooling can cause more harm than good.
Also notice that I directly used a reference to the Marten IDocumentSession rather than wrapping some kind of IRepository<Loan> or IAccountRepository abstraction right around Marten. That was very purposeful. I think those abstractions — especially narrow, entity-centric abstractions around basic CRUD or load methods cause more harm than good in nontrivial enterprise systems. In the case above, I was using a touch of advanced, Marten-specific behavior to load related documents in one network round trip as a performance optimization. That’s the exact kind of powerful ability of specific persistence tools that’s thrown away by generic “IRepository of T” strategies “just in case we decide to change database technologies later” that I believe to be harmful in larger enterprise systems. Moreover, I think that kind of abstraction bloats the codebase and leads to poorly performing systems.
We’re dogfooding Wolverine at work and the Critter Stack Discord is pretty active right now. All of that means that issues and opportunities to improve Wolverine are coming in fast right now. I just pushed Wolverine 0.9.13 (the Nugets are all named “WolverineFx” something because someone is squatting on the “Wolverine” name in Nuget).
First, quick thanks to Robin Arrowsmith for finding and fixing an issue with Wolverine’s Azure Service Bus support. And a more general thank you to the nascent Wolverine community for being so helpful working with me in Discord to improve Wolverine.
A few folks are reporting various issues with Wolverine handler discovery. To help alleviate whatever those issues turn out to be, Wolverine has a new mechanism to troubleshoot “why is my handler not being found by Wolverine?!?” issues.
We’re converting a service at work that lives within a giant distributed system that’s using NServiceBus for messaging today, so weirdly enough, there’s some important improvements for Wolverine’s interoperability with NServiceBus.
This will be worth a full blog post soon, but there’s some ability to add contextual logging about your domain (account numbers, tenants, product numbers, etc.) to Wolverine’s open telemetry and/or logging support. My personal goal here is to have all the necessary and valuable correlation between system activity, performance, and logged problems without forcing the development team to write repetitive code throughout their message handler code.
And one massive bug fix for how Wolverine generates runtime code in conjunction with your IoC service registrations for objects created by Wolverine itself. That’s a huge amount of technical mumbo jumbo that amounts to “even though Jeremy really doesn’t approve, you can inject Marten IDocumentSession or EF Core DbContext objects into repository classes while still using Wolverine transactional middleware and outbox support.” See this issue for more context. It’s a hugely important fix for folks who choose to use Wolverine with a typical, .NET Onion/Clean architecture with lots of constructor injection, repository wrappers, and making the garbage collection work like crazy at runtime.
This post is mostly an attempt to gather feedback from anyone out there interested enough to respond. Comment here, or better yet, tell us and the community what you’re interested in in the Critter Stack Discord community.
The so called “Critter Stack” is Marten, Wolverine, and a host of smaller, shared supporting projects within the greater JasperFx umbrella. Marten has been around for while now, just hit the “1,000 closed pull request” milestone, and will reach the 4 million download mark sometime next week. Wolverine is getting some early adopter love right now, and the feedback is being very encouraging to me right now.
The goal for this year is to make the Critter Stack the best technical choice for a CQRS with Event Sourcing style architecture across every technical ecosystem — and a strong candidate for server side development on the .NET platform for other types of architectural strategies. That’s a bold goal, and there’s a lot to do to fill in missing features and increase the ability of the Critter Stack to scale up to extremely large workloads. To keep things moving, the core team banged out our immediate road map for the next couple months:
Marten 6.0 within a couple weeks. This isn’t a huge release in terms of API changes, but sets us up for the future
Wolverine 1.0 shortly after. I think I’m to the point of saying the main priority is finishing the documentation website and conducting some serious load and chaos testing against the Rabbit MQ and Marten integrations (weirdly enough the exact technical stack we’ll be using at my job)
Marten 6.1: Formal event subscription mechanisms as part of Marten (ability to selectively publish events to a listener of some sort or a messaging broker). You can do this today as shown in Oskar’s blog post, but it’s not a first class citizen and not as efficient as it should be. Plus you’d want both “hot” and “cold” subscriptions.
Wolverine 1.1: Direct support for the subscription model within Marten so that you have ready recipes to publish events from Marten with Wolverine’s messaging capabilities. Technically, you can already do this with Wolverine + Marten’s outbox integration, but that only works through Wolverine handlers. Adding the first class recipe for “Marten to Wolverine messaging” I think will make it awfully easy to get up and going with event subscriptions fast.
Right now, Marten 6 and Wolverine 1.0 have lingered for awhile, so it’s time to get them out. After that, subscriptions seem to be the biggest source of user questions and requests right now, so that’s the obvious next thing to do. After that though, here’s a rundown of some of the major initiatives we could pursue in either Marten or Wolverine this year (and some straddle the line):
End to end multi-tenancy support in Wolverine, Marten, and ASP.Net Core. Marten has strong support for multi-tenancy, but users have to piece things together themselves together within their applications. Wolverine’s Marten integration is currently limited to only one Marten database per application
Hot/cold storage for active vs archived events. This is all about massive scalability for the event sourcing storage
Sharding the asynchronous projections to distribute work across multiple running nodes. More about scaling the event sourcing
Zero down time projection rebuilds. Big user ask. Probably also includes trying to optimize the heck out of the performance of this feature too
More advanced message broker feature support. AWS SNS support. Azure Service Bus topics support. Message batching in Rabbit MQ
Improving the Linq querying in Marten. At some point soon, I’d like to try to utilize the sql/json support within Postgresql to try to improve the Linq query performance and fill in more gaps in the support. Especially for querying within child collections. And better Select() transform support. That’s a neverending battle.
Optimized serverless story in Wolverine. Not exactly sure what this means, but I’m thinking to do something that tries to drastically reduce the “cold start” time
Open Telemetry support within Marten. It’s baked in with Wolverine, but not Marten yet. I think that’s going to be an opt in feature though
More persistence options within Wolverine. I’ll always be more interested in the full Wolverine + Marten stack, but I’d be curious to try out DynamoDb or CosmosDb support as well
There’s tons of other things to possibly do, but that list is what I’m personally most interested in our community getting to this year. No way there’s enough bandwidth for everything, so it’s time to start asking folks what they want out of these tools in the near future.
Today I’m taking a left turn in Albuquerque to talk about how to deal with injecting fake services in integration test scenarios for external service gateways in Wolverine applications using some tricks in the underlying Lamar IoC container — or really just anything that turns out to be difficult to deal with in automated tests.
Since this is a headless service, I’m not too keen on introducing Alba or WebApplicationFactory and all their humongous tail of ASP.Net Core dependencies. Instead, I made a mild change to the Program file of the main application to revert back to the “old” .NET 6 style of bootstrapping instead of the newer, implied Program.Main() style strictly to facilitate integration testing:
public static class Program
{
public static Task<int> Main(string[] args)
{
return CreateHostBuilder().RunOaktonCommands(args);
}
// This method is a really easy way to bootstrap the application
// in testing later
public static IHostBuilder CreateHostBuilder()
{
return Host.CreateDefaultBuilder()
.UseWolverine((context, opts) =>
{
// And a lot of necessary configuration here....
});
}
}
Now, I’m going to start a new xUnit.Net project to test the main application (NUnit or MSTest would certainly be viable as well). In the testing project, I want to test the payment ingestion service from the prior blog posts with basically the exact same set up as the main application, with the exception of replacing the service gateway for the “very unreliable 3rd party service” with a stub that we can control at will during testing. That stub could look like this:
// More on this later...
public interface IStatefulStub
{
void ClearState();
}
public class ThirdPartyServiceStub : IThirdPartyServiceGateway, IStatefulStub
{
public Dictionary<Guid, LoanInformation> LoanInformation { get; } = new();
public Task<LoanInformation> FindLoanInformationAsync(Guid loanId, CancellationToken cancellation)
{
if (LoanInformation.TryGetValue(loanId, out var information))
{
return Task.FromResult(information);
}
// I suppose you'd throw a more specific exception type, but I'm lazy, so....
throw new ArgumentOutOfRangeException(nameof(loanId), "Unknown load id");
}
public Task PostPaymentScheduleAsync(PaymentSchedule schedule, CancellationToken cancellation)
{
PostedSchedules.Add(schedule);
return Task.CompletedTask;
}
public List<PaymentSchedule> PostedSchedules { get; } = new();
public void ClearState()
{
PostedSchedules.Clear();
LoanInformation.Clear();
}
}
Now that we have a usable stub for later, let’s build up a test harness for our application. Right off the bat, I’m going to say that we won’t even try to run integration tests in parallel, so I’m going for a shared context that bootstraps the applications IHost:
public class AppFixture : IAsyncLifetime
{
public async Task InitializeAsync()
{
// This is bootstrapping the actual application using
// its implied Program.Main() set up
Host = await Program.CreateHostBuilder()
// This is from Lamar, this will override the service registrations
// no matter what order registrations are done. This was specifically
// intended for automated testing scenarios
.OverrideServices(services =>
{
// Override the existing application's registration with a stub
// for the third party service gateway
services.AddSingleton<IThirdPartyServiceGateway>(ThirdPartyService);
}).StartAsync();
}
// Just a convenient way to get at this later
public ThirdPartyServiceStub ThirdPartyService { get; } = new();
public IHost Host { get; private set; }
public Task DisposeAsync()
{
return Host.StopAsync();
}
}
So a couple comments about the code up above:
I’m delegating to the Program.CreateHostBuilder() method from our real application to create an IHostBuilder that is exactly the application itself. I think it’s important to do integration tests as close to the real application as possible so you don’t get false positives or false negatives from some sort of different bootstrapping or configuration of the application.
That being said, it’s absolutely going to be a pain in the ass to use the real “unreliable 3rd party service” in integration testing, so it would be very convenient to have a nice, easily controlled stub or “spy” we can use to capture data sent to the 3rd party or to set up responses from the 3rd party service
And no, we don’t know if your application actually works end to end if we use the whitebox testing approach, and there is very likely going to be unforeseen issues when we integrate with the real 3rd party service. All that being said, it’s very helpful to first know that our code works exactly the way we intended it to before we tackle fully end to end tests.
But if this were a real project, I’d spike the actual 3rd party gateway code ASAP because that’s likely where the major project risk is. In the real life project this was based on, that gateway code was not under my purview at first and I might have gotten myself temporarily banned from the client site after finally snapping at the developer “responsible” for that after about a year of misery. Moving on!
Lamar is StructureMap’s descendent, but it’s nowhere near as loosey-goosey flexible about runtime service overrides as StructureMap. That was very purposeful on my part as that led to Lamar having vastly better (1-3 orders of magnitude improvement) performance, and also to reduce my stress level by simplifying the Lamar usage over StructureMap’s endlessly complicated rules for service overrides. Long story short, that requires you to think through in advance a little bit about what services are going to be overridden in tests and to frankly use that sparingly compared to what was easy in StructureMap years ago.
Next, I’ll add the necessary xUnit ICollectionFixture type that I almost always forget to do at first unless I’m copy/pasting code from somewhere else:
[CollectionDefinition("integration")]
public class ScenarioCollection : ICollectionFixture<AppFixture>
{
}
Now, I like to have a base class for integration tests that just adds a tiny bit of reusable helpers and lifecycle methods to clean up the system state before all tests:
public abstract class IntegrationContext : IAsyncLifetime
{
public IntegrationContext(AppFixture fixture)
{
Host = fixture.Host;
Store = Host.Services.GetRequiredService<IDocumentStore>();
ThirdPartyService = fixture.ThirdPartyService;
}
public ThirdPartyServiceStub ThirdPartyService { get; set; }
public IHost Host { get; }
public IDocumentStore Store { get; }
async Task IAsyncLifetime.InitializeAsync()
{
// Using Marten, wipe out all data and reset the state
// back to exactly what we described in InitialAccountData
await Store.Advanced.ResetAllData();
// Clear out all the stateful stub state too!
// First, I'm getting at the broader Lamar service
// signature to do Lamar-specific things...
var container = (IContainer)Host.Services;
// Find every possible service that's registered in Lamar that implements
// the IStatefulStub interface, resolve them, and loop though them
// like so
foreach (var stub in container.Model.GetAllPossible<IStatefulStub>())
{
stub.ClearState();
}
}
// This is required because of the IAsyncLifetime
// interface. Note that I do *not* tear down database
// state after the test. That's purposeful
public Task DisposeAsync()
{
return Task.CompletedTask;
}
}
And now, some comments about that bit of code. You generally want a clean slate of system state going into each test, and our stub for the 3rd party system is stateful, so we’d want to clear it out between tests to keep from polluting the next test. That what the `IStatefulStub` interface and the calls to GetAllPossible() is helping us do with the Lamar container. If the system grows and we use more stubs, we can use that mechanism to have a one stop shop to clear out any stateful objects in the container between tests.
Lastly, here’s a taste of how the full test harness might be used:
public class ASampleTestHarness : IntegrationContext
{
public ASampleTestHarness(AppFixture fixture) : base(fixture)
{
}
[Fact]
public async Task how_the_test_might_work()
{
// Do the Arrange and Act part of the tests....
await Host.InvokeMessageAndWaitAsync(new PaymentValidated(new Payment()));
// Our test *should* have posted a single payment schedule
// within the larger workflow, and this will blow up if there's
// none or many
var schedule = ThirdPartyService.PostedSchedules.Single();
// Write assertions against the expected data for the schedule maybe?
}
}
I don’t like piecing together special application bootstrapping in the test automation projects, as that tends to drift apart from the actual application over time. Instead, I’d rather use the application’s own bootstrapping — in this case how it builds up an IHostBuilder — then apply some limited number of testing overrides.
Lamar has a couple helpers for test automation, including the OverrideServices() method and the GetAllPossible() helper that can be useful for clearing out state between tests in stubs or caches or who knows what else in a systematic way.
So far I’ve probably mostly blogged about things that Wolverine does that other tools like NServiceBus, MassTransit, or MediatR do as well. Next time out, I want to go completely off road where those tools can’t follow and into Wolverine’s “compound handler” strategy for maximum testability using Jim Shore’s A-Frame Architecture approach.
To review, I was describing a project I worked on years ago that involved some interactions with a very unreliable 3rd party web service system to handle payments originating from a flat file:
Just based on that diagram above, and admittedly some bad experiences in the shake down cruise of the historical system that diagram was based on, here’s some of the things that can go wrong:
The system blows up and dies while the payments from a particular file are only half way processed
Transient errors from database connectivity. Network hiccups
File IO errors from reading the flat files (I tend to treat direct file system access a lot like a poisonous snake due to very bad experiences early in my career)
HTTP errors from timeouts calling the web service
The 3rd party system is under distress and performing very poorly, such that a high percentage of requests are timing out
The 3rd party system can be misconfigured after code migrations on its system so that it’s technically “up” and responsive, but nothing actually works
The 3rd party system is completely down
Man, it’s a scary world sometimes!
Let’s say right now that our goal is as much as possible to have a system that is:
Able to recover from errors without losing any ongoing work
Doesn’t allow the system to permanently get into an inconsistent state — i.e. a file is marked as completely read, but somehow some of the payments from that file got lost along the way
Rarely needs manual intervention from production support to recover work or restart work
Heavens forbid, when something does happen that the system can’t recover from, it notifies production support
Now let’s go onto how to utilize Wolverine features to satisfy those goals in the face of all the potential problems I identified.
What if the system dies halfway through a file?
If you read through the last post, I used the local queueing mechanism in Wolverine to effectively create a producer/consumer workflow. Great! But what if the current process manages to die before all the ongoing work is completed? That’s where the durable inbox support in Wolverine comes in.
Pulling Marten in as our persistence strategy (but EF Core with either Postgresql or Sql Server is fully supported for this use case as well), I’m going to set up the application to opt into durable inbox mechanics for all locally queued messages like so (after adding the WolverineFx.Marten Nuget):
using Marten;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Oakton;
using Wolverine;
using Wolverine.Marten;
using WolverineIngestionService;
return await Host.CreateDefaultBuilder()
.UseWolverine((context, opts) =>
{
// There'd obviously be a LOT more set up and service registrations
// to be a real application
var connectionString = context.Configuration.GetConnectionString("marten");
opts.Services
.AddMarten(connectionString)
.IntegrateWithWolverine();
// I want all local queues in the application to be durable
opts.Policies.UseDurableLocalQueues();
opts.LocalQueueFor<PaymentValidated>().Sequential();
opts.LocalQueueFor<PostPaymentSchedule>().Sequential();
}).RunOaktonCommands(args);
And with those changes, all in flight messages in the local queues are also stored durably in the backing database. If the application process happens to fail in flight, the persisted messages will fail over to either another running node or be picked up by restarting the system process.
So far, so good? Onward…
Getting Over transient hiccups
Sometimes database interactions will fail with transient errors and will very well succeed if retried later. This is especially common when the database is under stress. Wolverine’s error handling policies easily accommodate that, and in this case I’m going to add some retry capabilities for basic database exceptions like so:
// Retry on basic database exceptions with some cooldown time in
// between retries
opts
.Policies
.OnException<NpgsqlException>()
.Or<MartenCommandException>()
.RetryWithCooldown(100.Milliseconds(), 250.Milliseconds(), 500.Milliseconds());
opts
.OnException<TimeoutException>()
.RetryWithCooldown(250.Milliseconds(), 500.Milliseconds());
Notice how I’ve specified some “cooldown” times for subsequent failures. This is more or less an example of exponential back off error handling that’s meant to effectively throttle a distressed subsystem to allow it to catch up and recover.
Now though, not every exception implies that the message may magically succeed at a later time, so in that case…
Walk away from bad apples
Over time we can recognize exceptions that pretty well mean that the message can never succeed. In that case we should just throw out the message instead of allowing it to suck down resources by being retried multiple times. Wolverine happily supports that as well. Let’s say that payment messages can never work if it refers to an account that cannot be found, so let’s do this:
// Just get out of there if the account referenced by a message
// does not exist!
opts
.OnException<UnknownAccountException>()
.Discard();
I should also note that Wolverine is writing to your application log when this happens.
Circuit Breakers to give the 3rd party system a timeout
As I’ve repeatedly said in this blog series so far, the “very unreliable 3rd party system” was somewhat less than reliable. What we found in practice was that the service would fail in bunches when it fell behind, but could recover over time. However, what would happen — even with the exponential back off policy — was that when the system was distressed it still couldn’t recover in time and continuing to pound it with retries just led to everything ending up in dead letter queues where it eventually required manual intervention to recover. That was exhausting and led to much teeth gnashing (and fingers pointed at me in angry meetings). In response to that, Wolverine comes with circuit breaker support as shown below:
// These are the queues that handle calls to the 3rd party web service
opts.LocalQueueFor<PaymentValidated>()
.Sequential()
// Add the circuit breaker
.CircuitBreaker(cb =>
{
// If the conditions are met to stop processing messages,
// Wolverine will attempt to restart in 5 minutes
cb.PauseTime = 5.Minutes();
// Stop listening if there are more than 20% failures
// over the tracking period
cb.FailurePercentageThreshold = 20;
// Consider the failures over the past minute
cb.TrackingPeriod = 1.Minutes();
// Get specific about what exceptions should
// be considered as part of the circuit breaker
// criteria
cb.Include<TimeoutException>();
// This is our fault, so don't shut off the listener
// when this happens
cb.Exclude<InvalidRequestException>();
});
opts.LocalQueueFor<PostPaymentSchedule>()
.Sequential()
// Or the defaults might be just fine
.CircuitBreaker();
With the set up above, if Wolverine detects too high a rate of message failures in a given time, it will completely stop message processing for that particular local queue. Since we’ve isolated the message processing for the two types of calls to the 3rd party web service, we’re allowing everything else to continue when the circuit breaker stops message processing. Do note that the circuit breaker functionality will try to restart message processing later after the designated pause time. Hopefully the pause time allows for the 3rd party system to recover — or for production support to make it recover. All of this without making all the backed up messages continuously fail and end up landing in the dead letter queues where it will take manual intervention to recover the work in progress.
Hold the line, the 3rd party system is broken!
On top of every thing else, the “very unreliable 3rd party system” was easily misconfigured at the drop of a hat such that it would become completely nonfunctional even though it appeared to be responsive. When this happened, every single message to that service would fail. So again, instead of letting all our pending work end up in the dead letter queue, let’s instead completely pause all message handling on the current local queue (wherever the error happened) if we can tell from the exception that the 3rd party system is nonfunctional like so:
// If we encounter this specific exception with this particular error code,
// it means that the 3rd party system is 100% nonfunctional even though it appears
// to be up, so let's pause all processing for 10 minutes
opts.OnException<ThirdPartyOperationException>(e => e.ErrorCode == 235)
.Requeue().AndPauseProcessing(10.Minutes());
Summary and next time!
It’s helpful to assign work within message handlers in such a way to maximize your error handling. Think hard about what actions in your system are prone to failure and may deserve to be their own individual message handler and messaging endpoint to allow for exact error handling policies like the way I used a circuit breaker on the queues that handled calls to the unreliable 3rd party service.
For my next post in this series, I think I want to make a diversion into integration testing using a stand in stub for the 3rd party service using the application setup with Lamar.
UPDATE: If you pull down the sample code, it’s not quite working with Swashbuckle yet. It *does* publish the metadata and the actual endpoints work, but it’s not showing up in the OpenAPI spec. Always something.
I just published Wolverine 0.9.10 to Nuget (after a much bigger 0.9.9 yesterday). There’s several bug fixes, some admitted breaking changes to advanced configuration items, and one significant change to the “mediator” behavior that’s described at the section at the very bottom of this post.
The big addition is a new library that enables Wolverine’s runtime model directly for HTTP endpoints in ASP.Net Core services without having to jump through the typical sequence of delegating directly from a Minimal API method directly to Wolverine’s mediator functionality like this:
Instead, Wolverine now has the WolverineFx.Http library to directly use Wolverine’s runtime model — including its unique middleware approach — directly from HTTP endpoints.
To bootstrap the application, I used the dotnet new webapi model, then added the WolverineFx.Marten and WolverineFx.HTTP nugets. The application bootstrapping for basic integration of Wolverine, Marten, and the new Wolverine HTTP model becomes:
using Marten;
using Oakton;
using Wolverine;
using Wolverine.Http;
using Wolverine.Marten;
var builder = WebApplication.CreateBuilder(args);
// Adding Marten for persistence
builder.Services.AddMarten(opts =>
{
opts.Connection(builder.Configuration.GetConnectionString("Marten"));
opts.DatabaseSchemaName = "todo";
})
.IntegrateWithWolverine()
.ApplyAllDatabaseChangesOnStartup();
// Wolverine usage is required for WolverineFx.Http
builder.Host.UseWolverine(opts =>
{
// This middleware will apply to the HTTP
// endpoints as well
opts.Policies.AutoApplyTransactions();
// Setting up the outbox on all locally handled
// background tasks
opts.Policies.UseDurableLocalQueues();
});
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
var app = builder.Build();
// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
app.UseSwagger();
app.UseSwaggerUI();
}
// Let's add in Wolverine HTTP endpoints to the routing tree
app.MapWolverineEndpoints();
return await app.RunOaktonCommands(args);
Do note that the only thing in that sample that pertains to WolverineFx.Http itself is the call to IEndpointRouteBuilder.MapWolverineEndpoints().
Let’s move on to “Hello, World” with a new Wolverine http endpoint from this class we’ll add to the sample project:
public class HelloEndpoint
{
[WolverineGet("/")]
public string Get() => "Hello.";
}
At application startup, WolverineFx.Http will find the HelloEndpoint.Get() method and treat it as a Wolverine http endpoint with the route pattern GET: / specified in the [WolverineGet] attribute.
As you’d expect, that route will write the return value back to the HTTP response and behave as specified by this Alba specification:
[Fact]
public async Task hello_world()
{
var result = await _host.Scenario(x =>
{
x.Get.Url("/");
x.Header("content-type").SingleValueShouldEqual("text/plain");
});
result.ReadAsText().ShouldBe("Hello.");
}
Moving on to the actual Todo problem domain, let’s assume we’ve got a class like this:
public class Todo
{
public int Id { get; set; }
public string? Name { get; set; }
public bool IsComplete { get; set; }
}
In a sample class called TodoEndpoints let’s add an HTTP service endpoint for listing all the known Todo documents:
[WolverineGet("/todoitems")]
public static Task<IReadOnlyList<Todo>> Get(IQuerySession session)
=> session.Query<Todo>().ToListAsync();
As you’d guess, this method will serialize all the known Todo documents from the database into the HTTP response and return a 200 status code. In this particular case the code is a little bit noisier than the Minimal API equivalent, but that’s okay, because you can happily use Minimal API and WolverineFx.Http together in the same project. WolverineFx.Http, however, will shine in more complicated endpoints.
Consider this endpoint just to return the data for a single Todo document:
// Wolverine can infer the 200/404 status codes for you here
// so there's no code noise just to satisfy OpenAPI tooling
[WolverineGet("/todoitems/{id}")]
public static Task<Todo?> GetTodo(int id, IQuerySession session, CancellationToken cancellation)
=> session.LoadAsync<Todo>(id, cancellation);
At this point it’s effectively de rigueur for any web service to support OpenAPI documentation directly in the service. Fortunately, WolverineFx.Http is able to glean most of the necessary metadata to support OpenAPI documentation with Swashbuckle from the method signature up above. The method up above will also cleanly set a status code of 404 if the requested Todo document does not exist.
Now, the bread and butter for WolverineFx.Http is using it in conjunction with Wolverine itself. In this sample, let’s create a new Todo based on submitted data, but also publish a new event message with Wolverine to do some background processing after the HTTP call succeeds. And, oh, yeah, let’s make sure this endpoint is actively using Wolverine’s transactional outbox support for consistency:
[WolverinePost("/todoitems")]
public static async Task<IResult> Create(CreateTodo command, IDocumentSession session, IMessageBus bus)
{
var todo = new Todo { Name = command.Name };
session.Store(todo);
// Going to raise an event within out system to be processed later
await bus.PublishAsync(new TodoCreated(todo.Id));
return Results.Created($"/todoitems/{todo.Id}", todo);
}
The endpoint code above is automatically enrolled in the Marten transactional middleware by simple virtue of having a dependency on Marten’s IDocumentSession. By also taking in the IMessageBus dependency, WolverineFx.Http is wrapping the transactional outbox behavior around the method so that the TodoCreated message is only sent after the database transaction succeeds.
Lastly for this page, consider the need to update a Todo from a PUT call. Your HTTP endpoint may vary its handling and response by whether or not the document actually exists. Just to show off Wolverine’s “composite handler” functionality and also how WolverineFx.Http supports middleware, consider this more complex endpoint:
public static class UpdateTodoEndpoint
{
public static async Task<(Todo? todo, IResult result)> LoadAsync(UpdateTodo command, IDocumentSession session)
{
var todo = await session.LoadAsync<Todo>(command.Id);
return todo != null
? (todo, new WolverineContinue())
: (todo, Results.NotFound());
}
[WolverinePut("/todoitems")]
public static void Put(UpdateTodo command, Todo todo, IDocumentSession session)
{
todo.Name = todo.Name;
todo.IsComplete = todo.IsComplete;
session.Store(todo);
}
}
In the WolverineFx.Http model, any bit of middleware that returns an IResult object is tested by the generated code to execute any IResult object returned from middleware that is not the built in WolverineContinue type and stop all further processing. This is intended to enable validation or authorization type middleware where you may need to filter calls to the inner HTTP handler.
With the sample application out of the way, here’s a rundown of the significant things about this library:
It’s actually a pretty small library in the greater scheme of things and all it really does is connect ASP.Net Core’s endpoint routing to the Wolverine runtime model — and Wolverine’s runtime model is likely going to be somewhat more efficient than Minimal API and much more efficient that MVC Core
It can be happily combined with Minimal API, MVC Core, or any other ASP.Net Core model that exploits endpoint routing, even within the same application
Wolverine is allowing you to use the Minimal API IResult model
The JSON serialization is strictly System.Text.Json and uses the same options as Minimal API within an ASP.Net Core application
It’s possible to use Wolverine middleware strategy with the HTTP endpoints
Wolverine is trying to glean necessary metadata from the method signatures to feed OpenAPI usage within ASP.Net Core without developers having to jump through hoops adding attributes or goofy TypedResult noise code just for Swashbuckle
This model plays nicely with Wolverine’s transactional outbox model for common cases where you need to both make database changes and publish additional messages for background processing in the same HTTP call. That’s a bit of important functionality that I feel is missing or is clumsy at best in many leading .NET server side technologies.
For the handful of you reading this that still remember FubuMVC, Wolverine’s HTTP model retains some of FubuMVC’s old strengths in terms of still not ramming framework concerns into your application code, but learned some hard lessons from FubuMVC’s ultimate failure:
FubuMVC was an ambitious, sprawling framework that was trying to be its own ecosystem with its own bootstrapping model, logging abstractions, and even IoC abstractions. WolverineFx.Http is just a citizen within the greater ASP.Net Core ecosystem and uses common .NET abstractions, concepts, and idiomatic naming conventions at every possible turn
FubuMVC relied too much on conventions, which was great when the convention was exactly what you needed, and kinda hurtful when you needed something besides the exact conventions. Not to worry, WolverineFx.Http let’s you drop right down to the HttpContext level at will or use any of the IResult objects in existing ASP.Net Core whenever the Wolverine conventions don’t fit.
FubuMVC could technically be used with old ASP.Net MVC, but it was a Frankenstein’s monster to pull off. Wolverine can be mixed and matched at will with either Minimal API, MVC Core, or even other OSS projects that exploit ASP.Net Core endpoint routing.
Wolverine is trying to play nicely in terms of OpenAPI metadata and security related metadata for usage of standard ASP.Net Core middleware like the authorization or authentication middleware
FubuMVC’s “Behavior” model gave you a very powerful “Russian Doll” middleware ability that was maximally flexible — and also maximally inefficient in runtime. Wolverine’s runtime model takes a very different approach to still allow for the “Russian Doll” flexibility, but to do so in a way that is more efficient at runtime than basically every other commonly used framework today in the .NET community.
When things went boom in FubuMVC, you got monumentally huge stack traces that could overwhelm developers who hadn’t had a week’s worth of good night sleeps. It sounds minor, but Wolverine is valuable in the sense that the stack traces from HTTP (or message handler) failures will have very minimal Wolverine related framework noise in the stack trace for easier readability by developers.
Big Change to In Memory Mediator Model
I’ve been caught off guard a bit by how folks have mostly been interested in Wolverine as an alternative to MediatR with typical usage like this where users just delegate to Wolverine in memory within a Minimal API route:
With the corresponding message handler being this:
public class ItemHandler
{
// This attribute applies Wolverine's EF Core transactional
// middleware
[Transactional]
public static ItemCreated Handle(
// This would be the message
CreateItemCommand command,
// Any other arguments are assumed
// to be service dependencies
ItemsDbContext db)
{
// Create a new Item entity
var item = new Item
{
Name = command.Name
};
// Add the item to the current
// DbContext unit of work
db.Items.Add(item);
// This event being returned
// by the handler will be automatically sent
// out as a "cascading" message
return new ItemCreated
{
Id = item.Id
};
}
}
Prior to the latest release, the ItemCreated event in the handler above when used from IMessageBus.InvokeAsync<ItemCreated>() was not published as a message because my original assumption was that in that case you were using the return value explicitly as a return value. Early users have been surprised that the ItemCreated was not published as a message, so I just changed the behavior to do so to make the cascading message behavior be more consistent and what folks seem to actually want.
The Shade Tree Developer 