Question 167840 in ASP.NET Question posted in
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Why is app.Run() middleware overriding a specific route mapping in ASP.NET Core?

  1. I have created a middleware using app.Map() that handles a specific route (/hello).
  2. However, when I add a second middleware using app.Run() that does not check for a specific route.
  3. It seems to overwrite the response of the first middleware even when a request is made to the /hello route.

I’m confused about why this is happening and how to fix it.

The code is below:

using Microsoft.Extensions.Primitives;
using System.Web;

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.Map("/hello", async (HttpContext context) => {

    context.Response.ContentType = "text/html";

    await context.Response.WriteAsync("Hello");
});

app.Run(async (HttpContext context) => {

    context.Response.ContentType = "text/html";

    await context.Response.WriteAsync("Bye");

});

app.Run();

I tried removing the app.Run() middleware then the specified ‘/hello’ middleware is executing.
But as soon as I add the app.Run() middleware again it then skips the middleware that is mapped to ‘/hello’;

Tags:

2

Answers


  1. 0

    Try switching to Use:

    app.Use(async (HttpContext context, Func<Task> next) =>
{
    await next();

    if (!context.Response.HasStarted)
    {
        context.Response.ContentType = "text/html";

        await context.Response.WriteAsync("Bye");
    }
});
app.Map("/hello", async (HttpContext context) => {
    context.Response.ContentType = "text/html";

    await context.Response.WriteAsync("Hello");
});

app.Run();

    I guess that the behaviour is due to the fact that the RunExtensions.Run adds something called "terminal middleware delegate".

    Also ASP.NET Core Middleware article can be useful.

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  2. 0

    You could check the source codes of RunExtensions.Run() method here

    public static class RunExtensions
{
    /// <summary>
    /// Adds a terminal middleware delegate to the application's request pipeline.
    /// </summary>
    /// <param name="app">The <see cref="IApplicationBuilder"/> instance.</param>
    /// <param name="handler">A delegate that handles the request.</param>
    public static void Run(this IApplicationBuilder app, RequestDelegate handler)
    {
        ArgumentNullException.ThrowIfNull(app);
        ArgumentNullException.ThrowIfNull(handler);

        app.Use(_ => handler);
    }
}

    it adds a middleware like

    app.Use(next => async (HttpContext context) =>
{
    context.Response.ContentType = "text/html";

    await context.Response.WriteAsync("Bye");

});

    if you don’t branch the pipeline ,your request would be shortcut

    You could try with Guru Stron’s solution or

    app.MapFallback(async (HttpContext context) =>
{
    context.Response.ContentType = "text/html";

    await context.Response.WriteAsync("Bye");
});

    Or branch the pipeline:

    app.Map("/hello",app=>app.Run(async (HttpContext context) =>
{

    context.Response.ContentType = "text/html";

    await context.Response.WriteAsync("Hello");
}));

    For your requirement

    You could check the difference:
    enter image description here
    enter image description here

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