HTTP Middleware

Creating and applying middleware to HTTP endpoints is very similar to middleware for message handlers with just a couple differences:

1. As shown in a later section, you can use IResult from ASP.Net Core Middleware for conditionally stopping request handling in addition to the HandlerContinuation approach from message handlers
2. Use the IHttpPolicy interface instead of IHandlerPolicy to conventionally apply middleware to only HTTP endpoints
3. Your middleware types can take in HttpContext and any other related services that Wolverine supports for HTTP endpoints in addition to IoC services

The [Middleware] attribute from message handlers works on HTTP endpoint methods.

Conditional Endpoint Continuations

For message handlers, you use the HandlerContinuation to conditionally stop message handling in middleware that executes before the main handler. Likewise, you can do the same thing in HTTP endpoints, but instead use the IResult concept from ASP.Net Core Minimal API.

As an example, let's say that you are using some middleware to do custom authentication filtering that stops processing with a 401 status code. Here's a bit of middleware from the Wolverine tests that does just that:

public class FakeAuthenticationMiddleware
{
    public static IResult Before(IAmAuthenticated message)
    {
        return message.Authenticated 
            // This tells Wolverine to just keep going
            ? WolverineContinue.Result() 
            
            // If the IResult is not WolverineContinue, Wolverine
            // will execute the IResult and stop processing otherwise
            : Results.Unauthorized();
    }
}

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Which is registered like this (or as described in Registering Middleware by Message Type):

opts.AddMiddlewareByMessageType(typeof(FakeAuthenticationMiddleware));
opts.AddMiddlewareByMessageType(typeof(CanShipOrderMiddleWare));

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The key point to notice there is that IResult is a "return value" of the middleware. In the case of an HTTP endpoint, Wolverine will check if that IResult is a WolverineContinue object, and if so, will continue processing. If the IResult object is anything else, Wolverine will execute that IResult and stop processing the HTTP request otherwise.

For a little more complex example, here's part of the Fluent Validation middleware for Wolverine.Http:

[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static async Task<IResult> ExecuteOne<T>(IValidator<T> validator, IProblemDetailSource<T> source, T message)
{
    // First, validate the incoming request of type T
    var result = await validator.ValidateAsync(message);
        
    // If there are any errors, create a ProblemDetails result and return
    // that to write out the validation errors and otherwise stop processing
    if (result.Errors.Any())
    {
        var details = source.Create(message, result.Errors);
        return Results.Problem(details);
    }

    // Everything is good, full steam ahead!
    return WolverineContinue.Result();
}

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Using Configure(chain) Methods

You can make explicit modifications to HTTP processing for middleware or OpenAPI metadata for a single endpoint (really all endpoint methods on that type) using the public static void Configure(HttpChain) convention.

Let's say you have a bit of custom middleware for HTTP endpoints like so:

public class StopwatchMiddleware
{
    private readonly Stopwatch _stopwatch = new();

    public void Before()
    {
        _stopwatch.Start();
    }

    public void Finally(ILogger logger, HttpContext context)
    {
        _stopwatch.Stop();
        logger.LogDebug("Request for route {Route} ran in {Duration} milliseconds",
            context.Request.Path, _stopwatch.ElapsedMilliseconds);
    }
}

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And you want to apply it to a single HTTP endpoint without having to dirty your hands with an attribute. You can use that naming convention up above like so:

sample: sample_applying_middleware_programmatically_to_one_chain

Apply Middleware by Policy

To apply middleware to selected HTTP endpoints by some kind of policy, you can use the IHttpPolicy type to analyze and apply middleware to some subset of HTTP endpoints. As an example from Wolverine.Http itself, this middleware is applied to any endpoint that also uses Wolverine message publishing to apply tracing information from the HttpContext to subsequent Wolverine messages published during the request:

public static class RequestIdMiddleware
{
    public const string CorrelationIdHeaderKey = "X-Correlation-ID";
    
    // Remember that most Wolverine middleware can be done with "just" a method
    public static void Apply(HttpContext httpContext, IMessageContext messaging)
    {
        if (httpContext.Request.Headers.TryGetValue(CorrelationIdHeaderKey, out var correlationId))
        {
            messaging.CorrelationId = correlationId.First();
        }
    }
}

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And a matching IHttpPolicy to apply that middleware to any HTTP endpoint where there is a dependency on Wolverine's IMessageContext or IMessageBus:

internal class RequestIdPolicy : IHttpPolicy
{
    public void Apply(IReadOnlyList<HttpChain> chains, GenerationRules rules, IContainer container)
    {
        foreach (var chain in chains)
        {
            var serviceDependencies = chain.ServiceDependencies(container, Type.EmptyTypes).ToArray();
            if (serviceDependencies.Contains(typeof(IMessageContext)) ||
                serviceDependencies.Contains(typeof(IMessageBus)))
            {
                chain.Middleware.Insert(0, new MethodCall(typeof(RequestIdMiddleware), nameof(RequestIdMiddleware.Apply)));
            }
        }
    }
}

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Lastly, this particular policy is included by default, but if it wasn't, this is the code to apply it explicitly:

// app is a WebApplication
app.MapWolverineEndpoints(opts =>
{
    // add the policy to Wolverine HTTP endpoints
    opts.AddPolicy<RequestIdPolicy>();
});

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For simpler middleware application, you could also use this feature:

app.MapWolverineEndpoints(opts =>
{
    // Fake policy to add authentication middleware to any endpoint classes under
    // an application namespace
    opts.AddMiddleware(typeof(MyAuthenticationMiddleware),
        c => c.HandlerCalls().Any(x => x.HandlerType.IsInNamespace("MyApp.Authenticated")));
});

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Required Inputs

Here's a common pattern in HTTP service development. Based on a route argument, you first load some kind of entity from persistence. If the data is not found, return a status code 404 that means the resource was not found, but otherwise continue working against that entity data you just loaded. To help remove boilerplate code, Wolverine.Http 1.2 introduced support for this pattern using the standard [Required] attribute on the parameters of the inputs to the HTTP handler methods. Here's an example that tries to apply an update to an existing Todo entity:

public record UpdateRequest(string Name, bool IsComplete);

public static class UpdateEndpoint
{
    // Find required Todo entity for the route handler below
    public static Task<Todo?> LoadAsync(int id, IDocumentSession session) 
        => session.LoadAsync<Todo>(id);
    
    [WolverinePut("/todos/{id:int}")]
    public static StoreDoc<Todo> Put(
        // Route argument
        int id,
        
        // The request body
        UpdateRequest request,
        
        // Entity loaded by the method above, 
        // but note the [Required] attribute
        [Required] Todo? todo)
    {
        todo.Name = request.Name;
        todo.IsComplete = request.IsComplete;

        return MartenOps.Store(todo);
    }
}

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You'll notice that the LoadAsync() method is looking up the Todo entity for the route parameter, where Wolverine would normally be passing that value to the matching Todo parameter of the main Put method. In this case though, because of the [Required] attribute, Wolverine.Http will stop processing with a 404 status code if the Todo cannot be found.

You can see this behavior in the generated code below:

    public class PUT_todos_id : Wolverine.Http.HttpHandler
    {
        private readonly Wolverine.Http.WolverineHttpOptions _wolverineHttpOptions;
        private readonly Marten.ISessionFactory _sessionFactory;

        public PUT_todos_id(Wolverine.Http.WolverineHttpOptions wolverineHttpOptions, Marten.ISessionFactory sessionFactory) : base(wolverineHttpOptions)
        {
            _wolverineHttpOptions = wolverineHttpOptions;
            _sessionFactory = sessionFactory;
        }



        public override async System.Threading.Tasks.Task Handle(Microsoft.AspNetCore.Http.HttpContext httpContext)
        {
            await using var documentSession = _sessionFactory.OpenSession();
            if (!int.TryParse((string)httpContext.GetRouteValue("id"), out var id))
            {
                httpContext.Response.StatusCode = 404;
                return;
            }


            var (request, jsonContinue) = await ReadJsonAsync<WolverineWebApi.Samples.UpdateRequest>(httpContext);
            if (jsonContinue == Wolverine.HandlerContinuation.Stop) return;
            var todo = await WolverineWebApi.Samples.UpdateEndpoint.LoadAsync(id, documentSession).ConfigureAwait(false);
            // 404 if this required object is null
            if (todo == null)
            {
                httpContext.Response.StatusCode = 404;
                return;
            }

            var storeDoc = WolverineWebApi.Samples.UpdateEndpoint.Put(id, request, todo);
            
            // Placed by Wolverine's ISideEffect policy
            storeDoc.Execute(documentSession);

            
            // Commit any outstanding Marten changes
            await documentSession.SaveChangesAsync(httpContext.RequestAborted).ConfigureAwait(false);

            // Wolverine automatically sets the status code to 204 for empty responses
            httpContext.Response.StatusCode = 204;
        }

    }

Lastly, Wolverine is also updating the OpenAPI metadata to reflect the possibility of a 404 response.