#5306: Implemented a background HttpContext factory.

This change instantiates an actual HttpContext object during background sweeps so that Razor templates using Html Helpers (that require HttpContext.Current to be not-null) won't fai lwhen being rendered.

src/Orchard/BackgroundHttpContext.cs

@@ -0,0 +1,38 @@
+using System.IO;
+using System.Web;
+using Orchard.Settings;
+
+namespace Orchard {
+    /// <summary>
+    /// A factory class that creates an HttpContext instance and initializes the HttpContext.Current property with that instance.
+    /// This is useful when rendering views from a background thread, as some Html Helpers access HttpContext.Current directly, thus preventing a NullReferenceException.
+    /// </summary>
+    public class BackgroundHttpContextFactory : IBackgroundHttpContextFactory {
+        public const string IsBackgroundHttpContextKey = "IsBackgroundHttpContext";
+        private readonly ISiteService _siteService;
+        public BackgroundHttpContextFactory(ISiteService siteService) {
+            _siteService = siteService;
+        }
+
+        public HttpContext CreateHttpContext() {
+            var url = _siteService.GetSiteSettings().BaseUrl;
+            var httpContext = new HttpContext(new HttpRequest("", url, ""), new HttpResponse(new StringWriter()));
+
+            httpContext.Items[IsBackgroundHttpContextKey] = true;
+
+            return httpContext;
+        }
+
+        public void InitializeHttpContext() {
+            if (HttpContext.Current != null)
+                return;
+
+            HttpContext.Current = CreateHttpContext();
+        }
+    }
+
+    public interface IBackgroundHttpContextFactory : IDependency {
+        HttpContext CreateHttpContext();
+        void InitializeHttpContext();
+    }
+}

src/Orchard/Mvc/HttpContextAccessor.cs

@@ -0,0 +1,39 @@
+using System;
+using System.Web;
+
+namespace Orchard.Mvc {
+    public class HttpContextAccessor : IHttpContextAccessor {
+        private HttpContextBase _httpContext;
+
+        public HttpContextBase Current() {
+            var httpContext = GetStaticProperty();
+            return !IsBackgroundHttpContext(httpContext) ? new HttpContextWrapper(httpContext) : _httpContext;
+        }
+
+        public void Set(HttpContextBase httpContext) {
+            _httpContext = httpContext;
+        }
+
+        private static bool IsBackgroundHttpContext(HttpContext httpContext) {
+            return httpContext == null || httpContext.Items.Contains(BackgroundHttpContextFactory.IsBackgroundHttpContextKey);
+        }
+
+        private static HttpContext GetStaticProperty() {
+            var httpContext = HttpContext.Current;
+            if (httpContext == null) {
+                return null;
+            }
+
+            try {
+                // The "Request" property throws at application startup on IIS integrated pipeline mode.
+                if (httpContext.Request == null) {
+                    return null;
+                }
+            }
+            catch (Exception) {
+                return null;
+            }
+            return httpContext;
+        }
+    }
+}

src/Orchard/Mvc/IHttpContextAccessor.cs

@@ -1,39 +1,8 @@
-using System;
-using System.Web;
+using System.Web;
 
 namespace Orchard.Mvc {
     public interface IHttpContextAccessor {
         HttpContextBase Current();
         void Set(HttpContextBase httpContext);
     }
-
-    public class HttpContextAccessor : IHttpContextAccessor {
-        private HttpContextBase _httpContext;
-
-        public HttpContextBase Current() {
-            var httpContext = GetStaticProperty();
-            return httpContext != null ? new HttpContextWrapper(httpContext) : _httpContext;
-        }
-
-        public void Set(HttpContextBase httpContext) {
-            _httpContext = httpContext;
-        }
-
-        private HttpContext GetStaticProperty() {
-            var httpContext = HttpContext.Current;
-            if (httpContext == null) {
-                return null;
-            }
-
-            try {
-                if (httpContext.Request == null) {
-                    return null;
-                }
-            }
-            catch (Exception) {
-                return null;
-            }
-            return httpContext;
-        }
-    }
 }

src/Orchard/Mvc/MvcModule.cs

@@ -28,7 +28,7 @@ namespace Orchard.Mvc {
                 return false;
 
             try {
-                // The "Request" property throws at application startup on IIS integrated pipeline mode
+                // The "Request" property throws at application startup on IIS integrated pipeline mode.
                 var req = HttpContext.Current.Request;
             }
             catch (Exception) {

src/Orchard/Orchard.Framework.csproj

@@ -317,6 +317,7 @@
     <Compile Include="Mvc\DataAnnotations\LocalizedRequiredAttribute.cs" />
     <Compile Include="Mvc\Extensions\RouteExtension.cs" />
     <Compile Include="Mvc\FormValueRequiredAttribute.cs" />
+    <Compile Include="Mvc\HttpContextAccessor.cs" />
     <Compile Include="Mvc\HttpContextWorkContext.cs" />
     <Compile Include="Mvc\Extensions\ControllerExtensions.cs" />
     <Compile Include="Mvc\IOrchardViewPage.cs" />
@@ -644,6 +645,7 @@
     <Compile Include="WebApi\Filters\OrchardApiActionFilterDispatcher.cs" />
     <Compile Include="WebApi\Routes\IHttpRouteProvider.cs" />
     <Compile Include="WebApi\Routes\StandardExtensionHttpRouteProvider.cs" />
+    <Compile Include="BackgroundHttpContext.cs" />
     <Compile Include="WorkContextExtensions.cs" />
     <Compile Include="Mvc\ViewEngines\Razor\RazorCompilationEventsShim.cs" />
     <Compile Include="Mvc\ViewEngines\Razor\RazorViewEngineProvider.cs" />

src/Orchard/Tasks/BackgroundService.cs

@@ -16,24 +16,28 @@ namespace Orchard.Tasks {
     public class BackgroundService : IBackgroundService {
         private readonly IEnumerable<IBackgroundTask> _tasks;
         private readonly ITransactionManager _transactionManager;
+        private readonly IBackgroundHttpContextFactory _backgroundHttpContextFactory;
         private readonly string _shellName;
-        private readonly IContentManager _contentManager;
 
         public BackgroundService(
             IEnumerable<IBackgroundTask> tasks, 
             ITransactionManager transactionManager, 
             ShellSettings shellSettings,
-            IContentManager contentManager) {
+            IContentManager contentManager,
+            IBackgroundHttpContextFactory backgroundHttpContextFactory) {
+
             _tasks = tasks;
             _transactionManager = transactionManager;
+            _backgroundHttpContextFactory = backgroundHttpContextFactory;
             _shellName = shellSettings.Name;
-            _contentManager = contentManager;
             Logger = NullLogger.Instance;
         }
 
         public ILogger Logger { get; set; }
 
         public void Sweep() {
+            _backgroundHttpContextFactory.InitializeHttpContext();
+
             foreach(var task in _tasks) {
                 var taskName = task.GetType().FullName;