Make UseIISIntegration idempotent (#274)

src/Microsoft.AspNetCore.Server.IISIntegration/Properties/AssemblyInfo.cs

@@ -3,6 +3,9 @@
 
 using System.Reflection;
 using System.Resources;
+using System.Runtime.CompilerServices;
+
+[assembly: InternalsVisibleTo("Microsoft.AspNetCore.Server.IISIntegration.Tests, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 
 [assembly: AssemblyMetadata("Serviceable", "True")]
 [assembly: NeutralResourcesLanguage("en-us")]

src/Microsoft.AspNetCore.Server.IISIntegration/WebHostBuilderIISExtensions.cs

@@ -30,12 +30,21 @@ namespace Microsoft.AspNetCore.Hosting
                 throw new ArgumentNullException(nameof(hostBuilder));
             }
 
+            // Check if `UseIISIntegration` was called already
+            if (hostBuilder.GetSetting(nameof(UseIISIntegration)) != null)
+            {
+                return hostBuilder;
+            }
+
             var port = hostBuilder.GetSetting(ServerPort) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{ServerPort}");
             var path = hostBuilder.GetSetting(ServerPath) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{ServerPath}");
             var pairingToken = hostBuilder.GetSetting(PairingToken) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{PairingToken}");
 
             if (!string.IsNullOrEmpty(port) && !string.IsNullOrEmpty(path) && !string.IsNullOrEmpty(pairingToken))
             {
+                // Set flag to prevent double service configuration
+                hostBuilder.UseSetting(nameof(UseIISIntegration), true.ToString());
+
                 var address = "http://localhost:" + port;
                 hostBuilder.CaptureStartupErrors(true);
 

test/Microsoft.AspNetCore.Server.IISIntegration.Tests/IISExtensionTests.cs

@@ -0,0 +1,33 @@
+// 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.Linq;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.TestHost;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Server.IISIntegration
+{
+    public class IISExtensionTests
+    {
+        [Fact]
+        public void CallingUseIISIntegrationMultipleTimesWorks()
+        {
+
+            var builder = new WebHostBuilder()
+                .UseSetting("TOKEN", "TestToken")
+                .UseSetting("PORT", "12345")
+                .UseSetting("APPL_PATH", "/")
+                .UseIISIntegration()
+                .UseIISIntegration()
+                .Configure(app => { });
+            var server = new TestServer(builder);
+
+            var filters = server.Host.Services.GetServices<IStartupFilter>()
+                .OfType<IISSetupFilter>();
+
+            Assert.Equal(1, filters.Count());
+        }
+    }
+}

test/Microsoft.AspNetCore.Server.IISIntegration.Tests/project.json

@@ -1,5 +1,8 @@
 {
   "version": "1.1.0-*",
+  "buildOptions": {
+    "keyFile": "../../tools/Key.snk"
+  },
   "dependencies": {
     "dotnet-test-xunit": "2.2.0-*",
     "Microsoft.AspNetCore.Server.IISIntegration": "1.1.0-*",