Why is the presence of middleware preventing execution of an endpoint? - asp.net

Question

I am a beginner at ASP.Net. Here is my startup.cs file:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.EntityFrameworkCore;
using CAPSWebServer.CapsDataModels;
namespace CAPSWebServer
{
public class Startup
{
public IConfiguration Configuration { get; set; }
public Startup(IConfiguration config)
{
Configuration = config;
}
// This method gets called by the runtime. Use this method to add services to the container.
// For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<CapsDataContext>(opts =>
{
opts.UseNpgsql(Configuration["ConnectionStrings:CAPSConnection"]);
opts.EnableSensitiveDataLogging(true);
});
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
app.UseStaticFiles();
app.UseRouting();
app.UseMiddleware<TestMiddleware>();
app.UseEndpoints(endpoints =>
{
endpoints.MapGet("/", async context =>
{
await context.Response.WriteAsync("Hello World!");
});
});
}
}
}
And here is my TestMiddleware class:
using Microsoft.AspNetCore.Http;
using System.Linq;
using System.Threading.Tasks;
using CAPSWebServer.CapsDataModels;
namespace CAPSWebServer
{
public class TestMiddleware
{
private RequestDelegate nextDelegate;
public TestMiddleware(RequestDelegate next)
{
nextDelegate = next;
}
public async Task Invoke(HttpContext context, CapsDataContext dataContext)
{
if (context.Request.Path == "/test")
{
await context.Response.WriteAsync($"There are {dataContext.Charges.Count()} charges.\n");
await context.Response.WriteAsync($"There are {dataContext.Inventories.Count()} coils.\n");
}
}
}
}
This application is configured to listen on port 500 of my computer. When I run localhost:5000/test, I get the expected report of how many charges and coils I have in my database. But when I run localhost:5000 by itself, I get nothing. I think I should be getting "Hello, world". If I comment out out the call to UseMiddleware(), I get "Hello, world". Why does the middleware block the endpoint?
I am using Visual Studio 2019.

Answer 1

You need to call the
nextDelegate();
So that the next middleware down the line is executed.
The reason it works when the URL contains "/test" is because you are writing directly into the response stream.