[Fixes #3068] TempData fails silently without sessions middleware

src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/SessionStateTempDataProvider.cs

@@ -59,16 +59,10 @@ public virtual IDictionary<string, object> LoadTempData(HttpContext context)
                 throw new ArgumentNullException(nameof(context));
             }
 
-            if (!IsSessionEnabled(context))
-            {
-                // Session middleware is not enabled. No-op
-                return null;
-            }
-
             var session = context.Session;
             if (session == null)
             {
-                return null;
+                throw new InvalidOperationException("Session cannot be null.");
             }
 
             var tempDataDictionary = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
@@ -162,6 +156,9 @@ public virtual void SaveTempData(HttpContext context, IDictionary<string, object
                 throw new ArgumentNullException(nameof(context));
             }
 
+            // Accessing Session property will throw if the session middleware is not enabled.
+            var session = context.Session;
+
             var hasValues = (values != null && values.Count > 0);
             if (hasValues)
             {
@@ -171,9 +168,6 @@ public virtual void SaveTempData(HttpContext context, IDictionary<string, object
                     EnsureObjectCanBeSerialized(item);
                 }
 
-                // Accessing Session property will throw if the session middleware is not enabled.
-                var session = context.Session;
-
                 using (var memoryStream = new MemoryStream())
                 {
                     using (var writer = new BsonWriter(memoryStream))
@@ -183,18 +177,12 @@ public virtual void SaveTempData(HttpContext context, IDictionary<string, object
                     }
                 }
             }
-            else if (IsSessionEnabled(context))
+            else
             {
-                var session = context.Session;
                 session.Remove(TempDataSessionStateKey);
             }
         }
 
-        private static bool IsSessionEnabled(HttpContext context)
-        {
-            return context.Features.Get<ISessionFeature>() != null;
-        }
-
         internal void EnsureObjectCanBeSerialized(object item)
         {
             var itemType = item.GetType();

src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/TempDataDictionary.cs

@@ -101,6 +101,13 @@ public object this[string key]
         /// <inheritdoc />
         public void Keep()
         {
+            // if the data is not loaded, we can assume none of it has been read
+            // and so silently return.
+            if (!_loaded)
+            {
+                return;
+            }
+
             Load();
             _retainedKeys.Clear();
             _retainedKeys.UnionWith(_data.Keys);

test/Microsoft.AspNet.Mvc.ViewFeatures.Test/ViewFeatures/SessionStateTempDataProviderTest.cs

@@ -16,52 +16,58 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
     public class SessionStateTempDataProviderTest
     {
         [Fact]
-        public void Load_NullSession_ReturnsEmptyDictionary()
+        public void Load_ThrowsException_WhenSessionIsNotBeingEnabled()
         {
             // Arrange
             var testProvider = new SessionStateTempDataProvider();
 
-            // Act
-            var tempDataDictionary = testProvider.LoadTempData(
-                GetHttpContext(session: null, sessionEnabled: true));
+            // Act & Assert
+            var exception = Assert.Throws<InvalidOperationException>(() => testProvider.LoadTempData(
+                GetHttpContext(session: null, sessionEnabled: false)));
 
-            // Assert
-            Assert.Null(tempDataDictionary);
+            Assert.Equal("Session has not been configured for this application or request.", exception.Message);
         }
 
         [Fact]
-        public void Load_NonNullSession_NoSessionData_ReturnsEmptyDictionary()
+        public void Save_ThrowsException_WhenSessionIsNotBeingEnabled()
         {
             // Arrange
             var testProvider = new SessionStateTempDataProvider();
+            var values = new Dictionary<string, object>();
+            values.Add("key1", "value1");
 
-            // Act
-            var tempDataDictionary = testProvider.LoadTempData(
-                GetHttpContext(Mock.Of<ISession>()));
+            // Act & Assert
+            var exception = Assert.Throws<InvalidOperationException>(() => testProvider.SaveTempData(
+                GetHttpContext(session: null, sessionEnabled: false), values));
 
-            // Assert
-            Assert.Empty(tempDataDictionary);
+            Assert.Equal("Session has not been configured for this application or request.", exception.Message);
         }
 
         [Fact]
-        public void Save_NullSession_NullDictionary_DoesNotThrow()
+        public void Load_NullSession_ReturnsEmptyDictionary()
         {
             // Arrange
             var testProvider = new SessionStateTempDataProvider();
 
-            // Act & Assert (does not throw)
-            testProvider.SaveTempData(GetHttpContext(session: null, sessionEnabled: false), null);
+            // Act & Assert
+            var exception = Assert.Throws<InvalidOperationException>(() => testProvider.LoadTempData(
+                GetHttpContext(session: null, sessionEnabled: true)));
+
+            Assert.Equal("Session cannot be null.", exception.Message);
         }
 
         [Fact]
-        public void Save_NullSession_EmptyDictionary_DoesNotThrow()
+        public void Load_NonNullSession_NoSessionData_ReturnsEmptyDictionary()
         {
             // Arrange
             var testProvider = new SessionStateTempDataProvider();
 
-            // Act & Assert (does not throw)
-            testProvider.SaveTempData(
-                GetHttpContext(session: null, sessionEnabled: false), new Dictionary<string, object>());
+            // Act
+            var tempDataDictionary = testProvider.LoadTempData(
+                GetHttpContext(Mock.Of<ISession>()));
+
+            // Assert
+            Assert.Empty(tempDataDictionary);
         }
 
         [Fact]