Reload HostFilteringOptions on change

src/Microsoft.AspNetCore/WebHost.cs

@@ -5,12 +5,14 @@ using System;
 using System.IO;
 using System.Reflection;
 using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.HostFiltering;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
 
 namespace Microsoft.AspNetCore
 {
@@ -184,11 +186,20 @@ namespace Microsoft.AspNetCore
                 })
                 .ConfigureServices((hostingContext, services) =>
                 {
-                    var hosts = hostingContext.Configuration["AllowedHosts"]?.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries);
+                    // Fallback
-                    services.AddHostFiltering(options =>
+                    services.PostConfigure<HostFilteringOptions>(options =>
                     {
-                        options.AllowedHosts = (hosts?.Length > 0 ? hosts : new[] { "*" });
+                        if (options.AllowedHosts == null || options.AllowedHosts.Count == 0)
+                        {
+                            // "AllowedHosts": "localhost;127.0.0.1;[::1]"
+                            var hosts = hostingContext.Configuration["AllowedHosts"]?.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries);
+                            // Fall back to "*" to disable.
+                            options.AllowedHosts = (hosts?.Length > 0 ? hosts : new[] { "*" });
+                        }
                     });
+                    // Change notification
+                    services.AddSingleton<IOptionsChangeTokenSource<HostFilteringOptions>>(
+                        new ConfigurationChangeTokenSource<HostFilteringOptions>(hostingContext.Configuration));
 
                     services.AddTransient<IStartupFilter, HostFilteringStartupFilter>();
                 })

test/Microsoft.AspNetCore.Tests/WebHostTests.cs

@@ -1,7 +1,13 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
+using System.Threading;
+using Microsoft.AspNetCore.HostFiltering;
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Tests
@@ -14,5 +20,50 @@ namespace Microsoft.AspNetCore.Tests
             var builder = WebHost.CreateDefaultBuilder(new string[] { "--urls", "http://localhost:5001" });
             Assert.Equal("http://localhost:5001", builder.GetSetting(WebHostDefaults.ServerUrlsKey));
         }
+
+        [Fact]
+        public void WebHostConfiguration_HostFilterOptionsAreReloadable()
+        {
+            var host = WebHost.CreateDefaultBuilder()
+                .Configure(app => { })
+                .ConfigureAppConfiguration(configBuilder =>
+                {
+                    configBuilder.Add(new ReloadableMemorySource());
+                }).Build();
+            var config = host.Services.GetRequiredService<IConfiguration>();
+            var monitor = host.Services.GetRequiredService<IOptionsMonitor<HostFilteringOptions>>();
+            var options = monitor.CurrentValue;
+
+            Assert.Contains("*", options.AllowedHosts);
+
+            var changed = new ManualResetEvent(false);
+            monitor.OnChange(newOptions =>
+            {
+                changed.Set();
+            });
+
+            config["AllowedHosts"] = "NewHost";
+
+            Assert.True(changed.WaitOne(TimeSpan.FromSeconds(10)));
+            options = monitor.CurrentValue;
+            Assert.Contains("NewHost", options.AllowedHosts);
+        }
+
+        private class ReloadableMemorySource : IConfigurationSource
+        {
+            public IConfigurationProvider Build(IConfigurationBuilder builder)
+            {
+                return new ReloadableMemoryProvider();
+            }
+        }
+
+        private class ReloadableMemoryProvider : ConfigurationProvider
+        {
+            public override void Set(string key, string value)
+            {
+                base.Set(key, value);
+                OnReload();
+            }
+        }
     }
 }