LazyControllers.cs

using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Runtime.Loader;
using System.Threading;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc.ApplicationParts;
using Microsoft.AspNetCore.Mvc.Infrastructure;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Primitives;

namespace LazyControllers
{
    public class Startup
    {
        // 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.AddControllers();

            // Add the module loader as a singleton
            services.AddSingleton<ModuleLoader>();
            // Add the same module loader instance as an IActionDescriptorChangeProvider so we can trigger updates
            services.AddSingleton<IActionDescriptorChangeProvider>(sp => sp.GetRequiredService<ModuleLoader>());
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ModuleLoader moduleLoader)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseRouting();

            app.Use(async (context, next) =>
            {
                if (context.Request.Path.StartsWithSegments("/load/M1"))
                {
                    var module = AssemblyLoadContext.Default.LoadFromAssemblyPath(Path.Combine(Environment.CurrentDirectory, @"..\Module1\bin\Debug\netcoreapp3.1\Module1.dll"));
                    moduleLoader.AddType(module);
                }

                if (context.Request.Path.StartsWithSegments("/load/M2"))
                {
                    var module = AssemblyLoadContext.Default.LoadFromAssemblyPath(Path.Combine(Environment.CurrentDirectory, @"..\Module2\bin\Debug\netcoreapp3.1\Module2.dll"));
                    moduleLoader.AddType(module);
                }

                await next();
            });

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }

    public class ModuleLoader : ApplicationPart, IApplicationPartTypeProvider, IActionDescriptorChangeProvider
    {
        private ImmutableArray<TypeInfo> _types = ImmutableArray.Create<TypeInfo>();
        private CancellationTokenSource _cts = new();

        public ModuleLoader(ApplicationPartManager applicationPartManager)
        {
            applicationPartManager.ApplicationParts.Add(this);
        }

        public void AddType(Assembly assembly)
        {
            ImmutableInterlocked.Update(
                ref _types,
                static (types, a) => types.AddRange(a.GetTypes().Select(t => t.GetTypeInfo())),
                assembly);

            Interlocked.Exchange(ref _cts, new())?.Cancel();
        }

        public IChangeToken GetChangeToken()
        {
            return new CancellationChangeToken(_cts.Token);
        }

        public IEnumerable<TypeInfo> Types => _types;

        public override string Name => "Dynamic Module Loader Part";
    }
}