Display startup errors in ANCM (#8518)

src/Hosting/Hosting/src/GenericHost/GenericWebHostedService.cs

@@ -186,6 +186,7 @@ namespace Microsoft.AspNetCore.Hosting.Internal
             {
                 context.Response.StatusCode = 500;
                 context.Response.Headers[HeaderNames.CacheControl] = "no-cache";
+                context.Response.ContentType = "text/html; charset=utf-8";
                 return errorPage.ExecuteAsync(context);
             };
         }

src/Hosting/Hosting/src/Microsoft.AspNetCore.Hosting.csproj

@@ -12,6 +12,7 @@
   <ItemGroup>
     <Compile Include="$(SharedSourceRoot)RazorViews\*.cs" />
     <Compile Include="$(SharedSourceRoot)StackTrace\**\*.cs" />
+    <Compile Include="$(SharedSourceRoot)ErrorPage\**\*.cs" />
   </ItemGroup>
 
   <ItemGroup>

src/Hosting/Hosting/src/Resources.resx

@@ -117,15 +117,6 @@
   <resheader name="writer">
     <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
   </resheader>
-  <data name="ErrorPageHtml_Title" xml:space="preserve">
-    <value>Internal Server Error</value>
-  </data>
-  <data name="ErrorPageHtml_UnhandledException" xml:space="preserve">
-    <value>An error occurred while starting the application.</value>
-  </data>
-  <data name="ErrorPageHtml_UnknownLocation" xml:space="preserve">
-    <value>Unknown location</value>
-  </data>
   <data name="WebHostBuilder_SingleInstance" xml:space="preserve">
     <value>WebHostBuilder allows creation only of a single instance of WebHost</value>
   </data>

src/Servers/IIS/AspNetCoreModuleV2/CommonLib/ConfigurationSection.h

@@ -28,6 +28,7 @@
 #define CS_ASPNETCORE_HANDLER_SET_CURRENT_DIRECTORY      L"setCurrentDirectory"
 #define CS_ASPNETCORE_DISABLE_START_UP_ERROR_PAGE        L"disableStartUpErrorPage"
 #define CS_ENABLED                                       L"enabled"
+#define CS_ASPNETCORE_HANDLER_CALL_STARTUP_HOOK          L"callStartupHook"
 
 class ConfigurationSection: NonCopyable
 {

src/Servers/IIS/AspNetCoreModuleV2/CommonLib/ServerErrorHandler.h

@@ -9,31 +9,34 @@
 class ServerErrorHandler : public REQUEST_HANDLER
 {
 public:
+    ServerErrorHandler(IHttpContext& pContext, USHORT statusCode, USHORT subStatusCode, const std::string& statusText, HRESULT hr, HINSTANCE module, bool disableStartupPage, int page) noexcept
+        : ServerErrorHandler(pContext, statusCode, subStatusCode, statusText, hr, module, disableStartupPage, page, std::vector<byte>()) 
+    {
+    }
 
-    ServerErrorHandler(IHttpContext &pContext, USHORT statusCode, USHORT subStatusCode, std::string statusText, HRESULT hr, HINSTANCE moduleInstance, bool disableStartupPage, int page) noexcept
+    ServerErrorHandler(IHttpContext& pContext, USHORT statusCode, USHORT subStatusCode, const std::string& statusText, HRESULT hr, HINSTANCE module, bool disableStartupPage, int page, const std::vector<byte>& content) noexcept
         : REQUEST_HANDLER(pContext),
-          m_pContext(pContext),
+        m_pContext(pContext),
-          m_HR(hr),
+        m_HR(hr),
-          m_disableStartupPage(disableStartupPage),
+        m_disableStartupPage(disableStartupPage),
-          m_page(page),
+        m_statusCode(statusCode),
-          m_moduleInstance(moduleInstance),
+        m_subStatusCode(subStatusCode),
-          m_statusCode(statusCode),
+        m_statusText(std::move(statusText)),
-          m_subStatusCode(subStatusCode),
+        m_page(page),
-          m_statusText(std::move(statusText))
+        m_ExceptionInfoContent(content),
+        m_moduleInstance(module)
     {
     }
 
     REQUEST_NOTIFICATION_STATUS ExecuteRequestHandler() override
     {
-        static std::string s_html500Page = GetHtml(m_moduleInstance, m_page);
+        WriteStaticResponse(m_pContext, m_HR, m_disableStartupPage);
-
-        WriteStaticResponse(m_pContext, s_html500Page, m_HR, m_disableStartupPage);
 
         return RQ_NOTIFICATION_FINISH_REQUEST;
     }
 
 private:
-    void WriteStaticResponse(IHttpContext& pContext, std::string &page, HRESULT hr, bool disableStartupErrorPage) const
+    void WriteStaticResponse(IHttpContext& pContext, HRESULT hr, bool disableStartupErrorPage) 
     {
         if (disableStartupErrorPage)
         {
@@ -49,14 +52,23 @@ private:
             (USHORT)strlen("text/html"),
             FALSE
         );
-        dataChunk.DataChunkType = HttpDataChunkFromMemory;
 
-        dataChunk.FromMemory.pBuffer = page.data();
+        dataChunk.DataChunkType = HttpDataChunkFromMemory;
-        dataChunk.FromMemory.BufferLength = static_cast<ULONG>(page.size());
+        if (m_ExceptionInfoContent.size() > 0)
+        {
+            dataChunk.FromMemory.pBuffer = &m_ExceptionInfoContent[0];
+            dataChunk.FromMemory.BufferLength = static_cast<ULONG>(m_ExceptionInfoContent.size());
+        }
+        else
+        {
+            static std::string s_html500Page = GetHtml(m_moduleInstance, m_page);
+            dataChunk.FromMemory.pBuffer = s_html500Page.data();
+            dataChunk.FromMemory.BufferLength = static_cast<ULONG>(s_html500Page.size());
+        }
+      
         pResponse->WriteEntityChunkByReference(&dataChunk);
     }
 
-    static
     std::string
     GetHtml(HMODULE module, int page)
     {
@@ -91,7 +103,7 @@ private:
         }
     }
 
-    IHttpContext &m_pContext;
+    IHttpContext& m_pContext;
     HRESULT m_HR;
     bool m_disableStartupPage;
     int m_page;
@@ -99,4 +111,5 @@ private:
     USHORT m_statusCode;
     USHORT m_subStatusCode;
     std::string m_statusText;
+    std::vector<byte> m_ExceptionInfoContent;
 };

src/Servers/IIS/AspNetCoreModuleV2/CommonLibTests/inprocess_application_tests.cpp

@@ -13,6 +13,7 @@ using ::testing::NiceMock;
 // Externals defined in inprocess
 BOOL       g_fProcessDetach;
 HANDLE     g_hEventLog;
+std::wstring g_exceptionEventLog;
 
 namespace InprocessTests
 {

src/Servers/IIS/AspNetCoreModuleV2/InProcessRequestHandler/InProcessOptions.cpp

@@ -57,6 +57,7 @@ InProcessOptions::InProcessOptions(const ConfigurationSource &configurationSourc
 
     const auto handlerSettings = aspNetCoreSection->GetKeyValuePairs(CS_ASPNETCORE_HANDLER_SETTINGS);
     m_fSetCurrentDirectory = equals_ignore_case(find_element(handlerSettings, CS_ASPNETCORE_HANDLER_SET_CURRENT_DIRECTORY).value_or(L"true"), L"true");
+    m_fCallStartupHook = equals_ignore_case(find_element(handlerSettings, CS_ASPNETCORE_HANDLER_CALL_STARTUP_HOOK).value_or(L"true"), L"true");
 
     m_dwStartupTimeLimitInMS = aspNetCoreSection->GetRequiredLong(CS_ASPNETCORE_PROCESS_STARTUP_TIME_LIMIT) * 1000;
     m_dwShutdownTimeLimitInMS = aspNetCoreSection->GetRequiredLong(CS_ASPNETCORE_PROCESS_SHUTDOWN_TIME_LIMIT) * 1000;

src/Servers/IIS/AspNetCoreModuleV2/InProcessRequestHandler/InProcessOptions.h

@@ -48,6 +48,12 @@ public:
         return m_fSetCurrentDirectory;
     }
 
+    bool
+    QueryCallStartupHook() const
+    {
+        return m_fCallStartupHook;
+    }
+
     bool
     QueryWindowsAuthEnabled() const
     {
@@ -116,6 +122,7 @@ private:
     bool                           m_fStdoutLogEnabled;
     bool                           m_fDisableStartUpErrorPage;
     bool                           m_fSetCurrentDirectory;
+    bool                           m_fCallStartupHook;
     bool                           m_fWindowsAuthEnabled;
     bool                           m_fBasicAuthEnabled;
     bool                           m_fAnonymousAuthEnabled;

src/Servers/IIS/AspNetCoreModuleV2/InProcessRequestHandler/StartupExceptionApplication.h

@@ -15,30 +15,28 @@ public:
         IHttpApplication& pApplication,
         HINSTANCE moduleInstance,
         BOOL disableLogs,
-        HRESULT hr)
+        HRESULT hr,
+        std::vector<byte>&& errorPageContent
+        )
         : m_disableLogs(disableLogs),
         m_HR(hr),
         m_moduleInstance(moduleInstance),
+        m_errorPageContent(std::move(errorPageContent)),
         InProcessApplicationBase(pServer, pApplication)
     {
     }
 
     ~StartupExceptionApplication() = default;
 
-    HRESULT CreateHandler(IHttpContext *pHttpContext, IREQUEST_HANDLER ** pRequestHandler)
+    HRESULT CreateHandler(IHttpContext* pHttpContext, IREQUEST_HANDLER** pRequestHandler)
     {
-        *pRequestHandler = new ServerErrorHandler(*pHttpContext, 500, 30, "Internal Server Error", m_HR, m_moduleInstance, m_disableLogs, IN_PROCESS_RH_STATIC_HTML);
+        *pRequestHandler = new ServerErrorHandler(*pHttpContext, 500, 30, "Internal Server Error", m_HR, m_moduleInstance, m_disableLogs, IN_PROCESS_RH_STATIC_HTML, m_errorPageContent);
+
         return S_OK;
     }
 
-    std::string&
-        GetStaticHtml500Content()
-    {
-        return html500Page;
-    }
-
 private:
-    std::string html500Page;
+    std::vector<byte> m_errorPageContent;
     BOOL m_disableLogs;
     HRESULT m_HR;
     HINSTANCE m_moduleInstance;

src/Servers/IIS/AspNetCoreModuleV2/InProcessRequestHandler/dllmain.cpp

@@ -28,6 +28,7 @@ HINSTANCE           g_hWinHttpModule;
 HINSTANCE           g_hAspNetCoreModule;
 HANDLE              g_hEventLog = NULL;
 bool                g_fInProcessApplicationCreated = false;
+std::vector<byte>   g_errorPageContent;
 HINSTANCE           g_hServerModule;
 
 HRESULT
@@ -128,7 +129,7 @@ CreateApplication(
             std::unique_ptr<InProcessOptions> options;
             THROW_IF_FAILED(InProcessOptions::Create(*pServer, pSite, *pHttpApplication, options));
             // Set the currently running application to a fake application that returns startup exceptions.
-            auto pErrorApplication = std::make_unique<StartupExceptionApplication>(*pServer, *pHttpApplication, g_hServerModule, options->QueryDisableStartUpErrorPage(), hr);
+            auto pErrorApplication = std::make_unique<StartupExceptionApplication>(*pServer, *pHttpApplication, g_hServerModule, options->QueryDisableStartUpErrorPage(), hr, std::move(g_errorPageContent));
 
             RETURN_IF_FAILED(pErrorApplication->StartMonitoringAppOffline());
             *ppApplication = pErrorApplication.release();

src/Servers/IIS/AspNetCoreModuleV2/InProcessRequestHandler/inprocessapplication.cpp

@@ -235,8 +235,26 @@ IN_PROCESS_APPLICATION::ExecuteApplication()
             LOG_INFOF(L"Setting current directory to %s", this->QueryApplicationPhysicalPath().c_str());
         }
 
-        bool clrThreadExited;
+        if (m_pConfig->QueryCallStartupHook())
+        {
+            // Used to display developer exception page when there is an exception in main.
+            auto currentStartupHookEnv = Environment::GetEnvironmentVariableValue(DOTNETCORE_STARTUP_HOOK);
 
+            if (currentStartupHookEnv.has_value())
+            {
+                currentStartupHookEnv = currentStartupHookEnv.value() + L";" + ASPNETCORE_STARTUP_ASSEMBLY;
+                LOG_LAST_ERROR_IF(!SetEnvironmentVariable(DOTNETCORE_STARTUP_HOOK, currentStartupHookEnv.value().c_str()));
+            }
+            else
+            {
+                LOG_LAST_ERROR_IF(!SetEnvironmentVariable(DOTNETCORE_STARTUP_HOOK, ASPNETCORE_STARTUP_ASSEMBLY));
+            }
+        }
+
+        // Used to make .NET Runtime always log to event log when there is an unhandled exception.
+        LOG_LAST_ERROR_IF(SetEnvironmentVariable(L"COMPlus_UseEntryPointFilter", L"1"));
+
+        bool clrThreadExited;
         {
             auto redirectionOutput = LoggingHelpers::CreateOutputs(
                     m_pConfig->QueryStdoutLogEnabled(),

src/Servers/IIS/AspNetCoreModuleV2/InProcessRequestHandler/inprocessapplication.h

@@ -15,6 +15,8 @@ typedef BOOL(WINAPI * PFN_SHUTDOWN_HANDLER) (void* pvShutdownHandlerContext);
 typedef REQUEST_NOTIFICATION_STATUS(WINAPI * PFN_ASYNC_COMPLETION_HANDLER)(void *pvManagedHttpContext, HRESULT hrCompletionStatus, DWORD cbCompletion);
 typedef void(WINAPI * PFN_REQUESTS_DRAINED_HANDLER) (void* pvShutdownHandlerContext);
 
+#define DOTNETCORE_STARTUP_HOOK  L"DOTNET_STARTUP_HOOKS"
+#define ASPNETCORE_STARTUP_ASSEMBLY L"Microsoft.AspNetCore.Server.IIS"
 class IN_PROCESS_APPLICATION : public InProcessApplicationBase
 {
 public:
@@ -58,7 +60,6 @@ public:
     HRESULT
     LoadManagedApplication();
 
-
     void
     QueueStop();
 

src/Servers/IIS/AspNetCoreModuleV2/InProcessRequestHandler/managedexports.cpp

@@ -4,8 +4,11 @@
 #include "inprocessapplication.h"
 #include "inprocesshandler.h"
 #include "requesthandler_config.h"
+#include "EventLog.h"
 
 extern bool g_fInProcessApplicationCreated;
+extern std::vector<byte> g_errorPageContent;
+extern IHttpServer* g_pHttpServer;
 
 //
 // Initialization export
@@ -236,7 +239,7 @@ http_read_request_bytes(
     {
         return E_FAIL;
     }
-    IHttpRequest *pHttpRequest = (IHttpRequest*)pInProcessHandler->QueryHttpContext()->GetRequest();
+    IHttpRequest* pHttpRequest = (IHttpRequest*)pInProcessHandler->QueryHttpContext()->GetRequest();
 
     // Check if there is anything to read
     if (pHttpRequest->GetRemainingEntityBytes() > 0)
@@ -267,7 +270,7 @@ http_write_response_bytes(
     _In_ BOOL* pfCompletionExpected
 )
 {
-    IHttpResponse *pHttpResponse = (IHttpResponse*)pInProcessHandler->QueryHttpContext()->GetResponse();
+    IHttpResponse* pHttpResponse = (IHttpResponse*)pInProcessHandler->QueryHttpContext()->GetResponse();
     BOOL fAsync = TRUE;
     BOOL fMoreData = TRUE;
     DWORD dwBytesSent = 0;
@@ -291,7 +294,7 @@ http_flush_response_bytes(
     _Out_ BOOL* pfCompletionExpected
 )
 {
-    IHttpResponse *pHttpResponse = (IHttpResponse*)pInProcessHandler->QueryHttpContext()->GetResponse();
+    IHttpResponse* pHttpResponse = (IHttpResponse*)pInProcessHandler->QueryHttpContext()->GetResponse();
 
     BOOL fAsync = TRUE;
     DWORD dwBytesSent = 0;
@@ -316,7 +319,7 @@ http_websockets_read_bytes(
     _In_ BOOL* pfCompletionPending
 )
 {
-    IHttpRequest3 *pHttpRequest = (IHttpRequest3*)pInProcessHandler->QueryHttpContext()->GetRequest();
+    IHttpRequest3* pHttpRequest = (IHttpRequest3*)pInProcessHandler->QueryHttpContext()->GetRequest();
 
     BOOL fAsync = TRUE;
 
@@ -343,7 +346,7 @@ http_websockets_write_bytes(
     _In_ BOOL* pfCompletionExpected
 )
 {
-    IHttpResponse2 *pHttpResponse = (IHttpResponse2*)pInProcessHandler->QueryHttpContext()->GetResponse();
+    IHttpResponse2* pHttpResponse = (IHttpResponse2*)pInProcessHandler->QueryHttpContext()->GetResponse();
 
     BOOL fAsync = TRUE;
     BOOL fMoreData = TRUE;
@@ -371,7 +374,7 @@ http_websockets_flush_bytes(
     _In_ BOOL* pfCompletionExpected
 )
 {
-    IHttpResponse2 *pHttpResponse = (IHttpResponse2*)pInProcessHandler->QueryHttpContext()->GetResponse();
+    IHttpResponse2* pHttpResponse = (IHttpResponse2*)pInProcessHandler->QueryHttpContext()->GetResponse();
 
     BOOL fAsync = TRUE;
     BOOL fMoreData = TRUE;
@@ -504,4 +507,12 @@ set_main_handler(_In_ hostfxr_main_fn main)
     IN_PROCESS_APPLICATION::SetMainCallback(main);
 }
 
+EXTERN_C __MIDL_DECLSPEC_DLLEXPORT
+VOID
+http_set_startup_error_page_content(_In_ byte* errorPageContent, int length)
+{
+    g_errorPageContent.resize(length);
+    memcpy(&g_errorPageContent[0], errorPageContent, length);
+}
+
 // End of export

src/Servers/IIS/IIS/ref/Microsoft.AspNetCore.Server.IIS.csproj

@@ -8,6 +8,8 @@
     <Reference Include="Microsoft.AspNetCore.Authentication.Core"  />
     <Reference Include="Microsoft.AspNetCore.Connections.Abstractions"  />
     <Reference Include="Microsoft.AspNetCore.Hosting.Abstractions"  />
+    <Reference Include="Microsoft.Extensions.FileProviders.Physical"  />
+    <Reference Include="Microsoft.Extensions.TypeNameHelper.Sources"  />
     <Reference Include="System.IO.Pipelines"  />
     <Reference Include="System.Security.Principal.Windows"  />
   </ItemGroup>

src/Servers/IIS/IIS/src/Microsoft.AspNetCore.Server.IIS.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>netcoreapp3.0</TargetFramework>
@@ -14,8 +14,11 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <Compile Include="$(SharedSourceRoot)Buffers.MemoryPool\**\*.cs" />
+    <Compile Include="$(SharedSourceRoot)Buffers.MemoryPool\**\*.cs" LinkBase="Shared\" />
-    <Compile Include="$(SharedSourceRoot)HttpSys\**\*.cs" />
+    <Compile Include="$(SharedSourceRoot)HttpSys\**\*.cs" LinkBase="Shared\"/>
+    <Compile Include="$(SharedSourceRoot)StackTrace\**\*.cs" LinkBase="Shared\" />
+    <Compile Include="$(SharedSourceRoot)RazorViews\*.cs" LinkBase="Shared\" />
+    <Compile Include="$(SharedSourceRoot)ErrorPage\*.cs" LinkBase="Shared\" />
   </ItemGroup>
 
   <Target Name="ValidateNativeComponentsBuilt" AfterTargets="Build" >
@@ -32,6 +35,8 @@
     <Reference Include="Microsoft.AspNetCore.Authentication.Core" />
     <Reference Include="Microsoft.AspNetCore.Connections.Abstractions" />
     <Reference Include="Microsoft.AspNetCore.Hosting.Abstractions" />
+    <Reference Include="Microsoft.Extensions.FileProviders.Physical" />
+    <Reference Include="Microsoft.Extensions.TypeNameHelper.Sources" />
     <Reference Include="System.IO.Pipelines" />
     <Reference Include="System.Security.Principal.Windows" />
   </ItemGroup>

src/Servers/IIS/IIS/src/NativeMethods.cs

@@ -147,6 +147,9 @@ namespace Microsoft.AspNetCore.Server.IIS
         [DllImport(AspNetCoreModuleDll)]
         private static extern int http_get_authentication_information(IntPtr pInProcessHandler, [MarshalAs(UnmanagedType.BStr)] out string authType, out IntPtr token);
 
+        [DllImport(AspNetCoreModuleDll)]
+        private static extern unsafe int http_set_startup_error_page_content(byte* content, int contentLength);
+
         public static void HttpPostCompletion(IntPtr pInProcessHandler, int cbBytes)
         {
             Validate(http_post_completion(pInProcessHandler, cbBytes));
@@ -169,7 +172,7 @@ namespace Microsoft.AspNetCore.Server.IIS
             Validate(register_callbacks(pInProcessApplication, requestCallback, shutdownCallback, disconnectCallback, asyncCallback, requestsDrainedHandler, pvRequestContext, pvShutdownContext));
         }
 
-        public static unsafe int HttpWriteResponseBytes(IntPtr pInProcessHandler, HttpApiTypes.HTTP_DATA_CHUNK* pDataChunks, int nChunks, out bool fCompletionExpected)
+        internal static unsafe int HttpWriteResponseBytes(IntPtr pInProcessHandler, HttpApiTypes.HTTP_DATA_CHUNK* pDataChunks, int nChunks, out bool fCompletionExpected)
         {
             return http_write_response_bytes(pInProcessHandler, pDataChunks, nChunks, out fCompletionExpected);
         }
@@ -179,7 +182,7 @@ namespace Microsoft.AspNetCore.Server.IIS
             return http_flush_response_bytes(pInProcessHandler, fMoreData, out fCompletionExpected);
         }
 
-        public static unsafe HttpApiTypes.HTTP_REQUEST_V2* HttpGetRawRequest(IntPtr pInProcessHandler)
+        internal static unsafe HttpApiTypes.HTTP_REQUEST_V2* HttpGetRawRequest(IntPtr pInProcessHandler)
         {
             return http_get_raw_request(pInProcessHandler);
         }
@@ -219,7 +222,7 @@ namespace Microsoft.AspNetCore.Server.IIS
             Validate(http_set_managed_context(pInProcessHandler, pvManagedContext));
         }
 
-        public static IISConfigurationData HttpGetApplicationProperties()
+        internal static IISConfigurationData HttpGetApplicationProperties()
         {
             var iisConfigurationData = new IISConfigurationData();
             Validate(http_get_application_properties(ref iisConfigurationData));
@@ -247,7 +250,7 @@ namespace Microsoft.AspNetCore.Server.IIS
             return http_websockets_read_bytes(pInProcessHandler, pvBuffer, cbBuffer, pfnCompletionCallback, pvCompletionContext, out dwBytesReceived, out fCompletionExpected);
         }
 
-        public static unsafe int HttpWebsocketsWriteBytes(
+        internal static unsafe int HttpWebsocketsWriteBytes(
             IntPtr pInProcessHandler,
             HttpApiTypes.HTTP_DATA_CHUNK* pDataChunks,
             int nChunks,
@@ -297,6 +300,14 @@ namespace Microsoft.AspNetCore.Server.IIS
             Validate(http_get_authentication_information(pInProcessHandler, out authType, out token));
         }
 
+        internal static unsafe void HttpSetStartupErrorPageContent(byte[] content)
+        {
+            fixed(byte* bytePtr = content)
+            {
+                http_set_startup_error_page_content(bytePtr, content.Length);
+            }
+        }
+
         private static void Validate(int hr)
         {
             if (hr != HR_OK)

src/Servers/IIS/IIS/src/StartupHook.cs

@@ -0,0 +1,102 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.IO.Pipelines;
+using System.Reflection;
+using System.Runtime.InteropServices;
+using System.Security.Claims;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Hosting.Views;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
+using Microsoft.AspNetCore.Server.IIS;
+using Microsoft.Extensions.FileProviders;
+using Microsoft.Extensions.StackTrace.Sources;
+
+
+/// <summary>
+/// Startup hooks are pieces of code that will run before a users program main executes
+/// See: https://github.com/dotnet/core-setup/blob/master/Documentation/design-docs/host-startup-hook.md
+/// The type must be named StartupHook without any namespace, and should be internal.
+/// </summary>
+internal class StartupHook
+{
+    /// <summary>
+    /// Startup hooks are pieces of code that will run before a users program main executes
+    /// See: https://github.com/dotnet/core-setup/blob/master/Documentation/design-docs/host-startup-hook.md
+    /// </summary>
+    public static void Initialize()
+    {
+        if (!NativeMethods.IsAspNetCoreModuleLoaded())
+        {
+            // This means someone set the startup hook for Microsoft.AspNetCore.Server.IIS
+            // but are not running inprocess. Return at this point.
+            return;
+        }
+
+        var detailedErrors = Environment.GetEnvironmentVariable("ASPNETCORE_DETAILEDERRORS");
+        var enableStartupErrorPage = detailedErrors?.Equals("1", StringComparison.OrdinalIgnoreCase) ?? false;
+        enableStartupErrorPage |= detailedErrors?.Equals("true", StringComparison.OrdinalIgnoreCase) ?? false;
+
+        var aspnetCoreEnvironment = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
+        enableStartupErrorPage |= aspnetCoreEnvironment?.Equals("Development", StringComparison.OrdinalIgnoreCase) ?? false;
+
+        var dotnetEnvironment = Environment.GetEnvironmentVariable("DOTNET_ENVIRONMENT");
+        enableStartupErrorPage |= dotnetEnvironment?.Equals("Development", StringComparison.OrdinalIgnoreCase) ?? false;
+
+        if (!enableStartupErrorPage)
+        {
+            // Not running in development or detailed errors aren't enabled
+            return;
+        }
+
+        AppDomain.CurrentDomain.UnhandledException += (sender, eventArgs) =>
+        {
+            var exception = (Exception)eventArgs.ExceptionObject;
+
+            // Get the content root from IIS.
+            var iisConfigData = NativeMethods.HttpGetApplicationProperties();
+            var contentRoot = iisConfigData.pwzFullApplicationPath.TrimEnd(Path.DirectorySeparatorChar);
+
+            var model = new ErrorPageModel
+            {
+                RuntimeDisplayName = RuntimeInformation.FrameworkDescription
+            };
+
+            var systemRuntimeAssembly = typeof(System.ComponentModel.DefaultValueAttribute).GetTypeInfo().Assembly;
+            var assemblyVersion = new AssemblyName(systemRuntimeAssembly.FullName).Version.ToString();
+            var clrVersion = assemblyVersion;
+            model.RuntimeArchitecture = RuntimeInformation.ProcessArchitecture.ToString();
+            var currentAssembly = typeof(ErrorPage).GetTypeInfo().Assembly;
+            model.CurrentAssemblyVesion = currentAssembly
+                .GetCustomAttribute<AssemblyInformationalVersionAttribute>()
+                .InformationalVersion;
+            model.ClrVersion = clrVersion;
+            model.OperatingSystemDescription = RuntimeInformation.OSDescription;
+
+            var exceptionDetailProvider = new ExceptionDetailsProvider(
+                new PhysicalFileProvider(contentRoot),
+                sourceCodeLineCount: 6);
+
+            model.ErrorDetails = exceptionDetailProvider.GetDetails(exception);
+
+            var errorPage = new ErrorPage(model);
+
+            var stream = new MemoryStream();
+
+            // Never will go async because we are writing to a memory stream.
+            errorPage.ExecuteAsync(stream).GetAwaiter().GetResult();
+
+            // Get the raw content and set the error page.
+            stream.Position = 0;
+            var content = stream.ToArray();
+
+            NativeMethods.HttpSetStartupErrorPageContent(content);
+        };
+    }
+}

src/Servers/IIS/IIS/test/Common.FunctionalTests/Inprocess/StartupTests.cs

@@ -3,9 +3,11 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Net;
+using System.Text.RegularExpressions;
 using System.Threading;
 using System.Threading.Tasks;
 using System.Xml.Linq;
@@ -481,6 +483,7 @@ namespace Microsoft.AspNetCore.Server.IISIntegration.FunctionalTests
 
 
         private static Dictionary<string, Func<IISDeploymentParameters, string>> StandaloneConfigTransformations = InitStandaloneConfigTransformations();
+
         public static IEnumerable<object[]> StandaloneConfigTransformationsScenarios => StandaloneConfigTransformations.ToTheoryData();
 
         [ConditionalTheory]
@@ -572,6 +575,116 @@ namespace Microsoft.AspNetCore.Server.IISIntegration.FunctionalTests
             await request;
         }
 
+        [ConditionalTheory]
+        [RequiresIIS(IISCapability.PoolEnvironmentVariables)]
+        [RequiresNewHandler]
+        [InlineData("ASPNETCORE_ENVIRONMENT", "Development")]
+        [InlineData("DOTNET_ENVIRONMENT", "deVelopment")]
+        [InlineData("ASPNETCORE_DETAILEDERRORS", "1")]
+        [InlineData("ASPNETCORE_DETAILEDERRORS", "TRUE")]
+        public async Task ExceptionIsLoggedToEventLogAndPutInResponseWhenDeveloperExceptionPageIsEnabled(string environmentVariable, string value)
+        {
+            var deploymentParameters = Fixture.GetBaseDeploymentParameters();
+            deploymentParameters.TransformArguments((a, _) => $"{a} Throw");
+
+            // Deployment parameters by default set ASPNETCORE_DETAILEDERRORS to true
+            deploymentParameters.EnvironmentVariables["ASPNETCORE_DETAILEDERRORS"] = "";
+            deploymentParameters.EnvironmentVariables[environmentVariable] = value;
+
+            var deploymentResult = await DeployAsync(deploymentParameters);
+            var result = await deploymentResult.HttpClient.GetAsync("/");
+            Assert.False(result.IsSuccessStatusCode);
+
+            var content = await result.Content.ReadAsStringAsync();
+            Assert.Contains("InvalidOperationException", content);
+            Assert.Contains("TestSite.Program.Main", content);
+
+            StopServer();
+
+            VerifyDotnetRuntimeEventLog(deploymentResult);
+        }
+
+        [ConditionalFact]
+        [RequiresIIS(IISCapability.PoolEnvironmentVariables)]
+        [RequiresNewHandler]
+        public async Task ExceptionIsNotLoggedToResponseWhenStartupHookIsDisabled()
+        {
+            var deploymentParameters = Fixture.GetBaseDeploymentParameters();
+            deploymentParameters.TransformArguments((a, _) => $"{a} Throw");
+            deploymentParameters.EnvironmentVariables["ASPNETCORE_DETAILEDERRORS"] = "";
+            deploymentParameters.EnvironmentVariables["ASPNETCORE_ENVIRONMENT"] = "Development";
+            deploymentParameters.HandlerSettings["callStartupHook"] = "false";
+
+            var deploymentResult = await DeployAsync(deploymentParameters);
+            var result = await deploymentResult.HttpClient.GetAsync("/");
+            Assert.False(result.IsSuccessStatusCode);
+
+            var content = await result.Content.ReadAsStringAsync();
+            Assert.DoesNotContain("InvalidOperationException", content);
+
+            StopServer();
+
+            VerifyDotnetRuntimeEventLog(deploymentResult);
+        }
+
+        [ConditionalFact]
+        [RequiresNewHandler]
+        public async Task ExceptionIsLoggedToEventLogDoesNotWriteToResponse()
+        {
+            var deploymentParameters = Fixture.GetBaseDeploymentParameters();
+            deploymentParameters.TransformArguments((a, _) => $"{a} Throw");
+
+            // Deployment parameters by default set ASPNETCORE_DETAILEDERRORS to true
+            deploymentParameters.EnvironmentVariables["ASPNETCORE_DETAILEDERRORS"] = "";
+
+            var deploymentResult = await DeployAsync(deploymentParameters);
+            var result = await deploymentResult.HttpClient.GetAsync("/");
+            Assert.False(result.IsSuccessStatusCode);
+
+            var content = await result.Content.ReadAsStringAsync();
+            Assert.DoesNotContain("InvalidOperationException", content);
+
+            StopServer();
+
+            VerifyDotnetRuntimeEventLog(deploymentResult);
+        }
+
+        private static void VerifyDotnetRuntimeEventLog(IISDeploymentResult deploymentResult)
+        {
+            var entries = GetEventLogsFromDotnetRuntime(deploymentResult); 
+
+            var expectedRegex = new Regex("Exception Info: System\\.InvalidOperationException:", RegexOptions.Singleline);
+            var matchedEntries = entries.Where(entry => expectedRegex.IsMatch(entry.Message)).ToArray();
+            // There isn't a process ID to filter on here, so there can be duplicate entries from other tests.
+            Assert.True(matchedEntries.Length > 0);
+        }
+
+        private static IEnumerable<EventLogEntry> GetEventLogsFromDotnetRuntime(IISDeploymentResult deploymentResult)
+        {
+            var processStartTime = deploymentResult.HostProcess.StartTime.AddSeconds(-5);
+            var eventLog = new EventLog("Application");
+
+            for (var i = eventLog.Entries.Count - 1; i >= 0; i--)
+            {
+                var eventLogEntry = eventLog.Entries[i];
+                if (eventLogEntry.TimeGenerated < processStartTime)
+                {
+                    // If event logs is older than the process start time, we didn't find a match.
+                    break;
+                }
+
+                if (eventLogEntry.ReplacementStrings == null)
+                {
+                    continue;
+                }
+
+                if (eventLogEntry.Source == ".NET Runtime")
+                {
+                    yield return eventLogEntry;
+                }
+            }
+        }
+
         private static void MoveApplication(
             IISDeploymentParameters parameters,
             string subdirectory)

src/Servers/IIS/IIS/test/Common.FunctionalTests/MultiApplicationTests.cs

@@ -10,7 +10,6 @@ using Microsoft.AspNetCore.Server.IIS.FunctionalTests.Utilities;
 using Microsoft.AspNetCore.Server.IntegrationTesting;
 using Microsoft.AspNetCore.Server.IntegrationTesting.IIS;
 using Microsoft.AspNetCore.Testing.xunit;
-using Microsoft.Extensions.Logging;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Server.IISIntegration.FunctionalTests

src/Shared/ErrorPage/ErrorPage.cshtml

@@ -1,4 +1,4 @@
-@using System
+@using System
 @using System.Globalization
 @using System.Linq
 @using System.Net
@@ -15,20 +15,19 @@
     public ErrorPageModel Model { get; set; }
 }
 @{
-    Response.ContentType = "text/html; charset=utf-8";
     var location = string.Empty;
 }
 <!DOCTYPE html>
 <html lang="@CultureInfo.CurrentUICulture.TwoLetterISOLanguageName" xmlns="http://www.w3.org/1999/xhtml">
     <head>
         <meta charset="utf-8" />
-        <title>@Resources.ErrorPageHtml_Title</title>
+        <title>Internal Server Error</title>
         <style>
             <%$ include: ErrorPage.css %>
         </style>
     </head>
     <body>
-        <h1>@Resources.ErrorPageHtml_UnhandledException</h1>
+        <h1>An error occurred while starting the application.</h1>
         @foreach (var errorDetail in Model.ErrorDetails)
         {
             <div class="titleerror">@errorDetail.Error.GetType().Name: @{ Output.Write(HtmlEncodeAndReplaceLineBreaks(errorDetail.Error.Message)); }</div>
@@ -49,7 +48,7 @@
             }
             else
             {
-                <p class="location">@Resources.ErrorPageHtml_UnknownLocation</p>
+                <p class="location">Unknown location</p>
             }
 
             var reflectionTypeLoadException = errorDetail.Error as ReflectionTypeLoadException;

src/Shared/ErrorPage/ErrorPageModel.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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.Collections.Generic;

src/Shared/RazorViews/BaseView.cs

@@ -57,6 +57,23 @@ namespace Microsoft.Extensions.RazorViews
         /// </summary>
         protected JavaScriptEncoder JavaScriptEncoder { get; set; } = JavaScriptEncoder.Default;
 
+
+        /// <summary>
+        /// Execute an individual request
+        /// </summary>
+        /// <param name="stream">The stream to write to</param>
+        public async Task ExecuteAsync(Stream stream)
+        {
+            // We technically don't need this intermediate buffer if this method accepts a memory stream. 
+            var buffer = new MemoryStream();
+            Output = new StreamWriter(buffer, UTF8NoBOM, 4096, leaveOpen: true);
+            await ExecuteAsync();
+            await Output.FlushAsync();
+            Output.Dispose();
+            buffer.Seek(0, SeekOrigin.Begin);
+            await buffer.CopyToAsync(stream);
+        }
+
         /// <summary>
         /// Execute an individual request
         /// </summary>

src/Shared/StackTrace/StackFrame/StackTraceHelper.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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;