Routing to inline handlers

It is possible in ASP.NET Core to handle a request directly, that is, to not route to a controller action. We define inline handlers by using an extension method that specifies the HTTP verb and the template to match, as follows:

• MapGet: HTTP Get
• MapPost: HTTP Post
• MapPut: HTTP Put
• MapDelete: HTTP Delete
• MapVerb: Any named HTTP verb; for example, Get is the same as using MapGet

There are actually two extension methods, MapXXX and MapXXXMiddleware, the first taking a delegate and the second a middleware class. An example follows.

These methods offer two possible signatures (except for Map<verb>, which takes the HTTP verb) and take the following parameters:

• pattern: This is a route template.
• requestHandler: This is a handler that takes the current context (HttpContext) and returns a task.

Here are two examples. In the first, we are merely setting the response content type and writing some text to the output:

endpoints.MapGet(
    pattern: "DirectRoute",
    requestDelegate: async ctx =>
    {
        ctx.Response.ContentType = "text/plain";
        await ctx.Response.WriteAsync("Here's your response!");
    });

Here, we are adding a middleware to the response:

var newAppBuilder = endpoints.CreateApplicationBuilder();
newAppBuilder.UseMiddleware<ResponseMiddleware>();

endpoints.MapGet(
    pattern: "DirectMiddlewareRoute", newAppBuilder.Build());

ResponseMiddleware could be something like this:

publicclassResponseMiddleware
{
    privatereadonlyRequestDelegate _next;
 
    public ResponseMiddleware(RequestDelegate next)
    {
        this._next = next;
    }
 
    publicasyncTask InvokeAsync(HttpContext ctx)
    {
        await ctx.Response.WriteAsync("Hello, from a middleware!");
    }
}

The two approaches, using a handler or the application builder, are similar, as the former gives us direct access to the request context, while the latter allows us to add steps to the request pipeline for a particular route template. It all depends on what you want to do.

Now that we understand how to handle routing requests, next we'll learn how to constrain the applicability of a route.