Restructure response caching middleware flow

- Always add IresponseCachingFeatu8re before calling the next middleware #81
- Use If-Modified-Since instead of the incorrect If-Unmodified-Since header #83
- Handle proxy-revalidate in the same way as must-revalidate #83
- Handle max-stale with no specified limit #83
- Bypass cache lookup for no-cache but store the response #83
- Bypass response capturing and buffering when no-store is specified #83
- Replace IsRequestCacheable cache policy with three new independent policy checks to reflect these changes
- Modify middleware flow to accommodate cache policy updates

src/Microsoft.AspNetCore.ResponseCaching/Internal/Interfaces/IResponseCachingPolicyProvider.cs

@@ -6,21 +6,35 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
     public interface IResponseCachingPolicyProvider
     {
         /// <summary>
-        /// Determine wehther the response cache middleware should be executed for the incoming HTTP request.
+        /// Determine whether the response caching logic should be attempted for the incoming HTTP request.
         /// </summary>
         /// <param name="context">The <see cref="ResponseCachingContext"/>.</param>
-        /// <returns><c>true</c> if the request is cacheable; otherwise <c>false</c>.</returns>
+        /// <returns><c>true</c> if response caching logic should be attempted; otherwise <c>false</c>.</returns>
-        bool IsRequestCacheable(ResponseCachingContext context);
+        bool AttemptResponseCaching(ResponseCachingContext context);
 
         /// <summary>
-        /// Determine whether the response received by the middleware be cached for future requests.
+        /// Determine whether a cache lookup is allowed for the incoming HTTP request.
+        /// </summary>
+        /// <param name="context">The <see cref="ResponseCachingContext"/>.</param>
+        /// <returns><c>true</c> if cache lookup for this request is allowed; otherwise <c>false</c>.</returns>
+        bool AllowCacheLookup(ResponseCachingContext context);
+
+        /// <summary>
+        /// Determine whether storage of the response is allowed for the incoming HTTP request.
+        /// </summary>
+        /// <param name="context">The <see cref="ResponseCachingContext"/>.</param>
+        /// <returns><c>true</c> if storage of the response for this request is allowed; otherwise <c>false</c>.</returns>
+        bool AllowCacheStorage(ResponseCachingContext context);
+
+        /// <summary>
+        /// Determine whether the response received by the middleware can be cached for future requests.
         /// </summary>
         /// <param name="context">The <see cref="ResponseCachingContext"/>.</param>
         /// <returns><c>true</c> if the response is cacheable; otherwise <c>false</c>.</returns>
         bool IsResponseCacheable(ResponseCachingContext context);
 
         /// <summary>
-        /// Determine whether the response retrieved from the response cache is fresh and be served.
+        /// Determine whether the response retrieved from the response cache is fresh and can be served.
         /// </summary>
         /// <param name="context">The <see cref="ResponseCachingContext"/>.</param>
         /// <returns><c>true</c> if the cached entry is fresh; otherwise <c>false</c>.</returns>

src/Microsoft.AspNetCore.ResponseCaching/Internal/LoggerExtensions.cs

@@ -31,7 +31,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
         private static Action<ILogger, int, Exception> _logResponseWithUnsuccessfulStatusCodeNotCacheable;
         private static Action<ILogger, Exception> _logNotModifiedIfNoneMatchStar;
         private static Action<ILogger, EntityTagHeaderValue, Exception> _logNotModifiedIfNoneMatchMatched;
-        private static Action<ILogger, DateTimeOffset, DateTimeOffset, Exception> _logNotModifiedIfUnmodifiedSinceSatisfied;
+        private static Action<ILogger, DateTimeOffset, DateTimeOffset, Exception> _logNotModifiedIfModifiedSinceSatisfied;
         private static Action<ILogger, Exception> _logNotModifiedServed;
         private static Action<ILogger, Exception> _logCachedResponseServed;
         private static Action<ILogger, Exception> _logGatewayTimeoutServed;
@@ -40,6 +40,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
         private static Action<ILogger, Exception> _logResponseCached;
         private static Action<ILogger, Exception> _logResponseNotCached;
         private static Action<ILogger, Exception> _logResponseContentLengthMismatchNotCached;
+        private static Action<ILogger, TimeSpan, TimeSpan, Exception> _logExpirationInfiniteMaxStaleSatisfied;
 
         static LoggerExtensions()
         {
@@ -70,7 +71,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
             _logExpirationMustRevalidate = LoggerMessage.Define<TimeSpan, TimeSpan>(
                 logLevel: LogLevel.Debug,
                 eventId: 7,
-                formatString: "The age of the entry is {Age} and has exceeded the maximum age of {MaxAge} specified by the 'max-age' cache directive. It must be revalidated because the 'must-revalidate' cache directive is specified.");
+                formatString: "The age of the entry is {Age} and has exceeded the maximum age of {MaxAge} specified by the 'max-age' cache directive. It must be revalidated because the 'must-revalidate' or 'proxy-revalidate' cache directive is specified.");
             _logExpirationMaxStaleSatisfied = LoggerMessage.Define<TimeSpan, TimeSpan, TimeSpan>(
                 logLevel: LogLevel.Debug,
                 eventId: 8,
@@ -119,10 +120,10 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
                 logLevel: LogLevel.Debug,
                 eventId: 19,
                 formatString: $"The ETag {{ETag}} in the '{HeaderNames.IfNoneMatch}' header matched the ETag of a cached entry.");
-            _logNotModifiedIfUnmodifiedSinceSatisfied = LoggerMessage.Define<DateTimeOffset, DateTimeOffset>(
+            _logNotModifiedIfModifiedSinceSatisfied = LoggerMessage.Define<DateTimeOffset, DateTimeOffset>(
                 logLevel: LogLevel.Debug,
                 eventId: 20,
-                formatString: $"The last modified date of {{LastModified}} is before the date {{IfUnmodifiedSince}} specified in the '{HeaderNames.IfUnmodifiedSince}' header.");
+                formatString: $"The last modified date of {{LastModified}} is before the date {{IfModifiedSince}} specified in the '{HeaderNames.IfModifiedSince}' header.");
             _logNotModifiedServed = LoggerMessage.Define(
                 logLevel: LogLevel.Information,
                 eventId: 21,
@@ -155,6 +156,10 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
                 logLevel: LogLevel.Warning,
                 eventId: 28,
                 formatString: $"The response could not be cached for this request because the '{HeaderNames.ContentLength}' did not match the body length.");
+            _logExpirationInfiniteMaxStaleSatisfied = LoggerMessage.Define<TimeSpan, TimeSpan>(
+                logLevel: LogLevel.Debug,
+                eventId: 29,
+                formatString: "The age of the entry is {Age} and has exceeded the maximum age of {MaxAge} specified by the 'max-age' cache directive. However, the 'max-stale' cache directive was specified without an assigned value and a stale response of any age is accepted.");
         }
 
         internal static void LogRequestMethodNotCacheable(this ILogger logger, string method)
@@ -252,9 +257,9 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
             _logNotModifiedIfNoneMatchMatched(logger, etag, null);
         }
 
-        internal static void LogNotModifiedIfUnmodifiedSinceSatisfied(this ILogger logger, DateTimeOffset lastModified, DateTimeOffset ifUnmodifiedSince)
+        internal static void LogNotModifiedIfModifiedSinceSatisfied(this ILogger logger, DateTimeOffset lastModified, DateTimeOffset ifModifiedSince)
         {
-            _logNotModifiedIfUnmodifiedSinceSatisfied(logger, lastModified, ifUnmodifiedSince, null);
+            _logNotModifiedIfModifiedSinceSatisfied(logger, lastModified, ifModifiedSince, null);
         }
 
         internal static void LogNotModifiedServed(this ILogger logger)
@@ -296,5 +301,10 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
         {
             _logResponseContentLengthMismatchNotCached(logger, null);
         }
+
+        internal static void LogExpirationInfiniteMaxStaleSatisfied(this ILogger logger, TimeSpan age, TimeSpan maxAge)
+        {
+            _logExpirationInfiniteMaxStaleSatisfied(logger, age, maxAge, null);
+        }
     }
 }

src/Microsoft.AspNetCore.ResponseCaching/Internal/ResponseCachingContext.cs

@@ -37,7 +37,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
 
         internal ILogger Logger { get; }
 
-        internal bool ShouldCacheResponse { get;  set; }
+        internal bool ShouldCacheResponse { get; set; }
 
         internal string BaseKey { get;  set; }
 

src/Microsoft.AspNetCore.ResponseCaching/Internal/ResponseCachingPolicyProvider.cs

@@ -10,10 +10,11 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
 {
     public class ResponseCachingPolicyProvider : IResponseCachingPolicyProvider
     {
-        public virtual bool IsRequestCacheable(ResponseCachingContext context)
+        public virtual bool AttemptResponseCaching(ResponseCachingContext context)
         {
-            // Verify the method
             var request = context.HttpContext.Request;
+
+            // Verify the method
             if (!HttpMethods.IsGet(request.Method) && !HttpMethods.IsHead(request.Method))
             {
                 context.Logger.LogRequestMethodNotCacheable(request.Method);
@@ -27,6 +28,13 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
                 return false;
             }
 
+            return true;
+        }
+
+        public virtual bool AllowCacheLookup(ResponseCachingContext context)
+        {
+            var request = context.HttpContext.Request;
+
             // Verify request cache-control parameters
             if (!StringValues.IsNullOrEmpty(request.Headers[HeaderNames.CacheControl]))
             {
@@ -50,6 +58,12 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
             return true;
         }
 
+        public virtual bool AllowCacheStorage(ResponseCachingContext context)
+        {
+            // Check request no-store
+            return !HeaderUtilities.ContainsCacheDirective(context.HttpContext.Request.Headers[HeaderNames.CacheControl], CacheControlHeaderValue.NoStoreString);
+        }
+
         public virtual bool IsResponseCacheable(ResponseCachingContext context)
         {
             var responseCacheControlHeader = context.HttpContext.Response.Headers[HeaderNames.CacheControl];
@@ -61,9 +75,8 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
                 return false;
             }
 
-            // Check no-store
+            // Check response no-store
-            if (HeaderUtilities.ContainsCacheDirective(context.HttpContext.Request.Headers[HeaderNames.CacheControl], CacheControlHeaderValue.NoStoreString)
+            if (HeaderUtilities.ContainsCacheDirective(responseCacheControlHeader, CacheControlHeaderValue.NoStoreString))
-                || HeaderUtilities.ContainsCacheDirective(responseCacheControlHeader, CacheControlHeaderValue.NoStoreString))
             {
                 context.Logger.LogResponseWithNoStoreNotCacheable();
                 return false;
@@ -187,17 +200,26 @@ namespace Microsoft.AspNetCore.ResponseCaching.Internal
                 // Validate max age
                 if (age >= lowestMaxAge)
                 {
-                    // Must revalidate
+                    // Must revalidate or proxy revalidate
-                    if (HeaderUtilities.ContainsCacheDirective(cachedCacheControlHeaders, CacheControlHeaderValue.MustRevalidateString))
+                    if (HeaderUtilities.ContainsCacheDirective(cachedCacheControlHeaders, CacheControlHeaderValue.MustRevalidateString)
+                        || HeaderUtilities.ContainsCacheDirective(cachedCacheControlHeaders, CacheControlHeaderValue.ProxyRevalidateString))
                     {
                         context.Logger.LogExpirationMustRevalidate(age, lowestMaxAge.Value);
                         return false;
                     }
 
                     TimeSpan? requestMaxStale;
+                    var maxStaleExist = HeaderUtilities.ContainsCacheDirective(requestCacheControlHeaders, CacheControlHeaderValue.MaxStaleString);
                     HeaderUtilities.TryParseSeconds(requestCacheControlHeaders, CacheControlHeaderValue.MaxStaleString, out requestMaxStale);
 
-                    // Request allows stale values
+                    // Request allows stale values with no age limit
+                    if (maxStaleExist && !requestMaxStale.HasValue)
+                    {
+                        context.Logger.LogExpirationInfiniteMaxStaleSatisfied(age, lowestMaxAge.Value);
+                        return true;
+                    }
+
+                    // Request allows stale values with age limit
                     if (requestMaxStale.HasValue && age - lowestMaxAge < requestMaxStale)
                     {
                         context.Logger.LogExpirationMaxStaleSatisfied(age, lowestMaxAge.Value, requestMaxStale.Value);

src/Microsoft.AspNetCore.ResponseCaching/ResponseCachingMiddleware.cs

@@ -74,39 +74,53 @@ namespace Microsoft.AspNetCore.ResponseCaching
             var context = new ResponseCachingContext(httpContext, _logger);
 
             // Should we attempt any caching logic?
-            if (_policyProvider.IsRequestCacheable(context))
+            if (_policyProvider.AttemptResponseCaching(context))
             {
                 // Can this request be served from cache?
-                if (await TryServeFromCacheAsync(context))
+                if (_policyProvider.AllowCacheLookup(context) && await TryServeFromCacheAsync(context))
                 {
                     return;
                 }
 
-                // Hook up to listen to the response stream
+                // Should we store the response to this request?
-                ShimResponseStream(context);
+                if (_policyProvider.AllowCacheStorage(context))
-
-                try
                 {
-                    // Subscribe to OnStarting event
+                    // Hook up to listen to the response stream
-                    httpContext.Response.OnStarting(_onStartingCallback, context);
+                    ShimResponseStream(context);
 
-                    await _next(httpContext);
+                    try
+                    {
+                        // Subscribe to OnStarting event
+                        httpContext.Response.OnStarting(_onStartingCallback, context);
 
-                    // If there was no response body, check the response headers now. We can cache things like redirects.
+                        await _next(httpContext);
-                    await OnResponseStartingAsync(context);
 
-                    // Finalize the cache entry
+                        // If there was no response body, check the response headers now. We can cache things like redirects.
-                    await FinalizeCacheBodyAsync(context);
+                        await OnResponseStartingAsync(context);
-                }
+
-                finally
+                        // Finalize the cache entry
-                {
+                        await FinalizeCacheBodyAsync(context);
-                    UnshimResponseStream(context);
+                    }
+                    finally
+                    {
+                        UnshimResponseStream(context);
+                    }
+
+                    return;
                 }
             }
-            else
+
+            // Response should not be captured but add IResponseCachingFeature which may be required when the response is generated
+            AddResponseCachingFeature(httpContext);
+
+            try
             {
                 await _next(httpContext);
             }
+            finally
+            {
+                RemoveResponseCachingFeature(httpContext);
+            }
         }
 
         internal async Task<bool> TryServeCachedResponseAsync(ResponseCachingContext context, IResponseCacheEntry cacheEntry)
@@ -220,6 +234,12 @@ namespace Microsoft.AspNetCore.ResponseCaching
                     (context.ResponseExpires - context.ResponseTime.Value) ??
                     DefaultExpirationTimeSpan;
 
+                // Generate a base key if none exist
+                if (string.IsNullOrEmpty(context.BaseKey))
+                {
+                    context.BaseKey = _keyProvider.CreateBaseKey(context);
+                }
+
                 // Check if any vary rules exist
                 if (!StringValues.IsNullOrEmpty(varyHeaders) || !StringValues.IsNullOrEmpty(varyQueryKeys))
                 {
@@ -279,9 +299,9 @@ namespace Microsoft.AspNetCore.ResponseCaching
 
         internal async Task FinalizeCacheBodyAsync(ResponseCachingContext context)
         {
-            var contentLength = context.HttpContext.Response.ContentLength;
             if (context.ShouldCacheResponse && context.ResponseCachingStream.BufferingEnabled)
             {
+                var contentLength = context.HttpContext.Response.ContentLength;
                 var bufferStream = context.ResponseCachingStream.GetBufferStream();
                 if (!contentLength.HasValue || contentLength == bufferStream.Length)
                 {
@@ -322,6 +342,15 @@ namespace Microsoft.AspNetCore.ResponseCaching
             }
         }
 
+        internal static void AddResponseCachingFeature(HttpContext context)
+        {
+            if (context.Features.Get<IResponseCachingFeature>() != null)
+            {
+                throw new InvalidOperationException($"Another instance of {nameof(ResponseCachingFeature)} already exists. Only one instance of {nameof(ResponseCachingMiddleware)} can be configured for an application.");
+            }
+            context.Features.Set<IResponseCachingFeature>(new ResponseCachingFeature());
+        }
+
         internal void ShimResponseStream(ResponseCachingContext context)
         {
             // Shim response stream
@@ -337,13 +366,12 @@ namespace Microsoft.AspNetCore.ResponseCaching
             }
 
             // Add IResponseCachingFeature
-            if (context.HttpContext.Features.Get<IResponseCachingFeature>() != null)
+            AddResponseCachingFeature(context.HttpContext);
-            {
-                throw new InvalidOperationException($"Another instance of {nameof(ResponseCachingFeature)} already exists. Only one instance of {nameof(ResponseCachingMiddleware)} can be configured for an application.");
-            }
-            context.HttpContext.Features.Set<IResponseCachingFeature>(new ResponseCachingFeature());
         }
 
+        internal static void RemoveResponseCachingFeature(HttpContext context) =>
+            context.Features.Set<IResponseCachingFeature>(null);
+
         internal static void UnshimResponseStream(ResponseCachingContext context)
         {
             // Unshim response stream
@@ -353,7 +381,7 @@ namespace Microsoft.AspNetCore.ResponseCaching
             context.HttpContext.Features.Set(context.OriginalSendFileFeature);
 
             // Remove IResponseCachingFeature
-            context.HttpContext.Features.Set<IResponseCachingFeature>(null);
+            RemoveResponseCachingFeature(context.HttpContext);
         }
 
         internal static bool ContentIsNotModified(ResponseCachingContext context)
@@ -388,8 +416,8 @@ namespace Microsoft.AspNetCore.ResponseCaching
             }
             else
             {
-                var ifUnmodifiedSince = context.HttpContext.Request.Headers[HeaderNames.IfUnmodifiedSince];
+                var ifModifiedSince = context.HttpContext.Request.Headers[HeaderNames.IfModifiedSince];
-                if (!StringValues.IsNullOrEmpty(ifUnmodifiedSince))
+                if (!StringValues.IsNullOrEmpty(ifModifiedSince))
                 {
                     DateTimeOffset modified;
                     if (!HeaderUtilities.TryParseDate(cachedResponseHeaders[HeaderNames.LastModified], out modified) &&
@@ -398,11 +426,11 @@ namespace Microsoft.AspNetCore.ResponseCaching
                         return false;
                     }
 
-                    DateTimeOffset unmodifiedSince;
+                    DateTimeOffset modifiedSince;
-                    if (HeaderUtilities.TryParseDate(ifUnmodifiedSince, out unmodifiedSince) &&
+                    if (HeaderUtilities.TryParseDate(ifModifiedSince, out modifiedSince) &&
-                        modified <= unmodifiedSince)
+                        modified <= modifiedSince)
                     {
-                        context.Logger.LogNotModifiedIfUnmodifiedSinceSatisfied(modified, unmodifiedSince);
+                        context.Logger.LogNotModifiedIfModifiedSinceSatisfied(modified, modifiedSince);
                         return true;
                     }
                 }

test/Microsoft.AspNetCore.ResponseCaching.Tests/ResponseCachingMiddlewareTests.cs

@@ -5,7 +5,9 @@ using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.ResponseCaching.Internal;
+using Microsoft.Extensions.Internal;
 using Microsoft.Extensions.Logging.Testing;
 using Microsoft.Extensions.Primitives;
 using Microsoft.Net.Http.Headers;
@@ -157,14 +159,14 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public void ContentIsNotModified_IfUnmodifiedSince_FallsbackToDateHeader()
+        public void ContentIsNotModified_IfModifiedSince_FallsbackToDateHeader()
         {
             var utcNow = DateTimeOffset.UtcNow;
             var sink = new TestSink();
             var context = TestUtils.CreateTestContext(sink);
             context.CachedResponseHeaders = new HeaderDictionary();
 
-            context.HttpContext.Request.Headers[HeaderNames.IfUnmodifiedSince] = HeaderUtilities.FormatDate(utcNow);
+            context.HttpContext.Request.Headers[HeaderNames.IfModifiedSince] = HeaderUtilities.FormatDate(utcNow);
 
             // Verify modifications in the past succeeds
             context.CachedResponseHeaders[HeaderNames.Date] = HeaderUtilities.FormatDate(utcNow - TimeSpan.FromSeconds(10));
@@ -183,19 +185,19 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             // Verify logging
             TestUtils.AssertLoggedMessages(
                 sink.Writes,
-                LoggedMessage.NotModifiedIfUnmodifiedSinceSatisfied,
+                LoggedMessage.NotModifiedIfModifiedSinceSatisfied,
-                LoggedMessage.NotModifiedIfUnmodifiedSinceSatisfied);
+                LoggedMessage.NotModifiedIfModifiedSinceSatisfied);
         }
 
         [Fact]
-        public void ContentIsNotModified_IfUnmodifiedSince_LastModifiedOverridesDateHeader()
+        public void ContentIsNotModified_IfModifiedSince_LastModifiedOverridesDateHeader()
         {
             var utcNow = DateTimeOffset.UtcNow;
             var sink = new TestSink();
             var context = TestUtils.CreateTestContext(sink);
             context.CachedResponseHeaders = new HeaderDictionary();
 
-            context.HttpContext.Request.Headers[HeaderNames.IfUnmodifiedSince] = HeaderUtilities.FormatDate(utcNow);
+            context.HttpContext.Request.Headers[HeaderNames.IfModifiedSince] = HeaderUtilities.FormatDate(utcNow);
 
             // Verify modifications in the past succeeds
             context.CachedResponseHeaders[HeaderNames.Date] = HeaderUtilities.FormatDate(utcNow + TimeSpan.FromSeconds(10));
@@ -217,20 +219,20 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             // Verify logging
             TestUtils.AssertLoggedMessages(
                 sink.Writes,
-                LoggedMessage.NotModifiedIfUnmodifiedSinceSatisfied,
+                LoggedMessage.NotModifiedIfModifiedSinceSatisfied,
-                LoggedMessage.NotModifiedIfUnmodifiedSinceSatisfied);
+                LoggedMessage.NotModifiedIfModifiedSinceSatisfied);
         }
 
         [Fact]
-        public void ContentIsNotModified_IfNoneMatch_Overrides_IfUnmodifiedSince_ToTrue()
+        public void ContentIsNotModified_IfNoneMatch_Overrides_IfModifiedSince_ToTrue()
         {
             var utcNow = DateTimeOffset.UtcNow;
             var sink = new TestSink();
             var context = TestUtils.CreateTestContext(sink);
             context.CachedResponseHeaders = new HeaderDictionary();
 
-            // This would fail the IfUnmodifiedSince checks
+            // This would fail the IfModifiedSince checks
-            context.HttpContext.Request.Headers[HeaderNames.IfUnmodifiedSince] = HeaderUtilities.FormatDate(utcNow);
+            context.HttpContext.Request.Headers[HeaderNames.IfModifiedSince] = HeaderUtilities.FormatDate(utcNow);
             context.CachedResponseHeaders[HeaderNames.LastModified] = HeaderUtilities.FormatDate(utcNow + TimeSpan.FromSeconds(10));
 
             context.HttpContext.Request.Headers[HeaderNames.IfNoneMatch] = EntityTagHeaderValue.Any.ToString();
@@ -241,15 +243,15 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public void ContentIsNotModified_IfNoneMatch_Overrides_IfUnmodifiedSince_ToFalse()
+        public void ContentIsNotModified_IfNoneMatch_Overrides_IfModifiedSince_ToFalse()
         {
             var utcNow = DateTimeOffset.UtcNow;
             var sink = new TestSink();
             var context = TestUtils.CreateTestContext(sink);
             context.CachedResponseHeaders = new HeaderDictionary();
 
-            // This would pass the IfUnmodifiedSince checks
+            // This would pass the IfModifiedSince checks
-            context.HttpContext.Request.Headers[HeaderNames.IfUnmodifiedSince] = HeaderUtilities.FormatDate(utcNow);
+            context.HttpContext.Request.Headers[HeaderNames.IfModifiedSince] = HeaderUtilities.FormatDate(utcNow);
             context.CachedResponseHeaders[HeaderNames.LastModified] = HeaderUtilities.FormatDate(utcNow - TimeSpan.FromSeconds(10));
 
             context.HttpContext.Request.Headers[HeaderNames.IfNoneMatch] = "\"E1\"";
@@ -328,27 +330,56 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_DoNotUpdateShouldCacheResponse_IfResponseIsNotCacheable()
+        public async Task OnResponseStartingAsync_IfAllowResponseCaptureIsTrue_SetsResponseTime()
         {
-            var sink = new TestSink();
+            var clock = new TestClock
-            var middleware = TestUtils.CreateTestMiddleware(testSink: sink, policyProvider: new ResponseCachingPolicyProvider());
+            {
+                UtcNow = DateTimeOffset.UtcNow
+            };
+            var middleware = TestUtils.CreateTestMiddleware(options: new ResponseCachingOptions
+            {
+                SystemClock = clock
+            });
             var context = TestUtils.CreateTestContext();
+            context.ResponseTime = null;
 
-            Assert.False(context.ShouldCacheResponse);
+            await middleware.OnResponseStartingAsync(context);
 
-            middleware.ShimResponseStream(context);
+            Assert.Equal(clock.UtcNow, context.ResponseTime);
-            await middleware.FinalizeCacheHeadersAsync(context);
-
-            Assert.False(context.ShouldCacheResponse);
-            Assert.Empty(sink.Writes);
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_UpdateShouldCacheResponse_IfResponseIsCacheable()
+        public async Task OnResponseStartingAsync_IfAllowResponseCaptureIsTrue_SetsResponseTimeOnlyOnce()
+        {
+            var clock = new TestClock
+            {
+                UtcNow = DateTimeOffset.UtcNow
+            };
+            var middleware = TestUtils.CreateTestMiddleware(options: new ResponseCachingOptions
+            {
+                SystemClock = clock
+            });
+            var context = TestUtils.CreateTestContext();
+            var initialTime = clock.UtcNow;
+            context.ResponseTime = null;
+
+            await middleware.OnResponseStartingAsync(context);
+            Assert.Equal(initialTime, context.ResponseTime);
+
+            clock.UtcNow += TimeSpan.FromSeconds(10);
+
+            await middleware.OnResponseStartingAsync(context);
+            Assert.NotEqual(clock.UtcNow, context.ResponseTime);
+            Assert.Equal(initialTime, context.ResponseTime);
+        }
+
+        [Fact]
+        public async Task FinalizeCacheHeadersAsync_UpdateShouldCacheResponse_IfResponseCacheable()
         {
             var sink = new TestSink();
             var middleware = TestUtils.CreateTestMiddleware(testSink: sink, policyProvider: new ResponseCachingPolicyProvider());
             var context = TestUtils.CreateTestContext();
+
             context.HttpContext.Response.Headers[HeaderNames.CacheControl] = new CacheControlHeaderValue()
             {
                 Public = true
@@ -363,7 +394,22 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_DefaultResponseValidity_Is10Seconds()
+        public async Task FinalizeCacheHeadersAsync_DoNotUpdateShouldCacheResponse_IfResponseIsNotCacheable()
+        {
+            var sink = new TestSink();
+            var middleware = TestUtils.CreateTestMiddleware(testSink: sink, policyProvider: new ResponseCachingPolicyProvider());
+            var context = TestUtils.CreateTestContext();
+
+            middleware.ShimResponseStream(context);
+
+            await middleware.FinalizeCacheHeadersAsync(context);
+
+            Assert.False(context.ShouldCacheResponse);
+            Assert.Empty(sink.Writes);
+        }
+
+        [Fact]
+        public async Task FinalizeCacheHeadersAsync_DefaultResponseValidity_Is10Seconds()
         {
             var sink = new TestSink();
             var middleware = TestUtils.CreateTestMiddleware(testSink: sink);
@@ -376,15 +422,21 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_ResponseValidity_UseExpiryIfAvailable()
+        public async Task FinalizeCacheHeadersAsync_ResponseValidity_UseExpiryIfAvailable()
         {
-            var utcNow = DateTimeOffset.MinValue;
+            var clock = new TestClock
+            {
+                UtcNow = DateTimeOffset.MinValue
+            };
             var sink = new TestSink();
-            var middleware = TestUtils.CreateTestMiddleware(testSink: sink);
+            var middleware = TestUtils.CreateTestMiddleware(testSink: sink, options: new ResponseCachingOptions
+            {
+                SystemClock = clock
+            });
             var context = TestUtils.CreateTestContext();
 
-            context.ResponseTime = utcNow;
+            context.ResponseTime = clock.UtcNow;
-            context.HttpContext.Response.Headers[HeaderNames.Expires] = HeaderUtilities.FormatDate(utcNow + TimeSpan.FromSeconds(11));
+            context.HttpContext.Response.Headers[HeaderNames.Expires] = HeaderUtilities.FormatDate(clock.UtcNow + TimeSpan.FromSeconds(11));
 
             await middleware.FinalizeCacheHeadersAsync(context);
 
@@ -393,17 +445,26 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_ResponseValidity_UseMaxAgeIfAvailable()
+        public async Task FinalizeCacheHeadersAsync_ResponseValidity_UseMaxAgeIfAvailable()
         {
+            var clock = new TestClock
+            {
+                UtcNow = DateTimeOffset.UtcNow
+            };
             var sink = new TestSink();
-            var middleware = TestUtils.CreateTestMiddleware(testSink: sink);
+            var middleware = TestUtils.CreateTestMiddleware(testSink: sink, options: new ResponseCachingOptions
+            {
+                SystemClock = clock
+            });
             var context = TestUtils.CreateTestContext();
+
+            context.ResponseTime = clock.UtcNow;
             context.HttpContext.Response.Headers[HeaderNames.CacheControl] = new CacheControlHeaderValue()
             {
                 MaxAge = TimeSpan.FromSeconds(12)
             }.ToString();
 
-            context.HttpContext.Response.Headers[HeaderNames.Expires] = HeaderUtilities.FormatDate(context.ResponseTime.Value + TimeSpan.FromSeconds(11));
+            context.HttpContext.Response.Headers[HeaderNames.Expires] = HeaderUtilities.FormatDate(clock.UtcNow + TimeSpan.FromSeconds(11));
 
             await middleware.FinalizeCacheHeadersAsync(context);
 
@@ -412,18 +473,26 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_ResponseValidity_UseSharedMaxAgeIfAvailable()
+        public async Task FinalizeCacheHeadersAsync_ResponseValidity_UseSharedMaxAgeIfAvailable()
         {
+            var clock = new TestClock
+            {
+                UtcNow = DateTimeOffset.UtcNow
+            };
             var sink = new TestSink();
-            var middleware = TestUtils.CreateTestMiddleware(testSink: sink);
+            var middleware = TestUtils.CreateTestMiddleware(testSink: sink, options: new ResponseCachingOptions
+            {
+                SystemClock = clock
+            });
             var context = TestUtils.CreateTestContext();
+
+            context.ResponseTime = clock.UtcNow;
             context.HttpContext.Response.Headers[HeaderNames.CacheControl] = new CacheControlHeaderValue()
             {
                 MaxAge = TimeSpan.FromSeconds(12),
                 SharedMaxAge = TimeSpan.FromSeconds(13)
             }.ToString();
-
+            context.HttpContext.Response.Headers[HeaderNames.Expires] = HeaderUtilities.FormatDate(clock.UtcNow + TimeSpan.FromSeconds(11));
-            context.HttpContext.Response.Headers[HeaderNames.Expires] = HeaderUtilities.FormatDate(context.ResponseTime.Value + TimeSpan.FromSeconds(11));
 
             await middleware.FinalizeCacheHeadersAsync(context);
 
@@ -432,7 +501,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_UpdateCachedVaryByRules_IfNotEquivalentToPrevious()
+        public async Task FinalizeCacheHeadersAsync_UpdateCachedVaryByRules_IfNotEquivalentToPrevious()
         {
             var cache = new TestResponseCache();
             var sink = new TestSink();
@@ -451,19 +520,17 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             };
             context.CachedVaryByRules = cachedVaryByRules;
 
-            await middleware.TryServeFromCacheAsync(context);
             await middleware.FinalizeCacheHeadersAsync(context);
 
             Assert.Equal(1, cache.SetCount);
             Assert.NotSame(cachedVaryByRules, context.CachedVaryByRules);
             TestUtils.AssertLoggedMessages(
                 sink.Writes,
-                LoggedMessage.NoResponseServed,
                 LoggedMessage.VaryByRulesUpdated);
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_UpdateCachedVaryByRules_IfEquivalentToPrevious()
+        public async Task FinalizeCacheHeadersAsync_UpdateCachedVaryByRules_IfEquivalentToPrevious()
         {
             var cache = new TestResponseCache();
             var sink = new TestSink();
@@ -483,7 +550,6 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             };
             context.CachedVaryByRules = cachedVaryByRules;
 
-            await middleware.TryServeFromCacheAsync(context);
             await middleware.FinalizeCacheHeadersAsync(context);
 
             // An update to the cache is always made but the entry should be the same
@@ -491,7 +557,6 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             Assert.Same(cachedVaryByRules, context.CachedVaryByRules);
             TestUtils.AssertLoggedMessages(
                 sink.Writes,
-                LoggedMessage.NoResponseServed,
                 LoggedMessage.VaryByRulesUpdated);
         }
 
@@ -515,7 +580,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
 
         [Theory]
         [MemberData(nameof(NullOrEmptyVaryRules))]
-        public async Task FinalizeCacheHeaders_UpdateCachedVaryByRules_NullOrEmptyRules(StringValues vary)
+        public async Task FinalizeCacheHeadersAsync_UpdateCachedVaryByRules_NullOrEmptyRules(StringValues vary)
         {
             var cache = new TestResponseCache();
             var sink = new TestSink();
@@ -528,40 +593,43 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
                 VaryByQueryKeys = vary
             });
 
-            await middleware.TryServeFromCacheAsync(context);
             await middleware.FinalizeCacheHeadersAsync(context);
 
             // Vary rules should not be updated
             Assert.Equal(0, cache.SetCount);
-            TestUtils.AssertLoggedMessages(
+            Assert.Empty(sink.Writes);
-                sink.Writes,
-                LoggedMessage.NoResponseServed);
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_DoNotAddDate_IfSpecified()
+        public async Task FinalizeCacheHeadersAsync_AddsDate_IfNoneSpecified()
         {
-            var utcNow = DateTimeOffset.MinValue;
+            var clock = new TestClock
+            {
+                UtcNow = DateTimeOffset.UtcNow
+            };
             var sink = new TestSink();
-            var middleware = TestUtils.CreateTestMiddleware(testSink: sink);
+            var middleware = TestUtils.CreateTestMiddleware(testSink: sink, options: new ResponseCachingOptions
+            {
+                SystemClock = clock
+            });
             var context = TestUtils.CreateTestContext();
-            context.ResponseTime = utcNow;
 
             Assert.True(StringValues.IsNullOrEmpty(context.HttpContext.Response.Headers[HeaderNames.Date]));
 
             await middleware.FinalizeCacheHeadersAsync(context);
 
-            Assert.Equal(HeaderUtilities.FormatDate(utcNow), context.HttpContext.Response.Headers[HeaderNames.Date]);
+            Assert.Equal(HeaderUtilities.FormatDate(clock.UtcNow), context.HttpContext.Response.Headers[HeaderNames.Date]);
             Assert.Empty(sink.Writes);
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_AddsDate_IfNoneSpecified()
+        public async Task FinalizeCacheHeadersAsync_DoNotAddDate_IfSpecified()
         {
             var utcNow = DateTimeOffset.MinValue;
             var sink = new TestSink();
             var middleware = TestUtils.CreateTestMiddleware(testSink: sink);
             var context = TestUtils.CreateTestContext();
+
             context.HttpContext.Response.Headers[HeaderNames.Date] = HeaderUtilities.FormatDate(utcNow);
             context.ResponseTime = utcNow + TimeSpan.FromSeconds(10);
 
@@ -574,7 +642,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_StoresCachedResponse_InState()
+        public async Task FinalizeCacheHeadersAsync_StoresCachedResponse_InState()
         {
             var sink = new TestSink();
             var middleware = TestUtils.CreateTestMiddleware(testSink: sink);
@@ -589,20 +657,19 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public async Task FinalizeCacheHeaders_SplitsVaryHeaderByCommas()
+        public async Task FinalizeCacheHeadersAsync_SplitsVaryHeaderByCommas()
         {
             var sink = new TestSink();
             var middleware = TestUtils.CreateTestMiddleware(testSink: sink);
             var context = TestUtils.CreateTestContext();
+
             context.HttpContext.Response.Headers[HeaderNames.Vary] = "HeaderB, heaDera";
 
-            await middleware.TryServeFromCacheAsync(context);
             await middleware.FinalizeCacheHeadersAsync(context);
 
             Assert.Equal(new StringValues(new[] { "HEADERA", "HEADERB" }), context.CachedVaryByRules.Headers);
             TestUtils.AssertLoggedMessages(
                 sink.Writes,
-                LoggedMessage.NoResponseServed,
                 LoggedMessage.VaryByRulesUpdated);
         }
 
@@ -614,11 +681,12 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             var middleware = TestUtils.CreateTestMiddleware(testSink: sink, cache: cache);
             var context = TestUtils.CreateTestContext();
 
+            context.ShouldCacheResponse = true;
             middleware.ShimResponseStream(context);
             context.HttpContext.Response.ContentLength = 20;
+
             await context.HttpContext.Response.WriteAsync(new string('0', 20));
 
-            context.ShouldCacheResponse = true;
             context.CachedResponse = new CachedResponse();
             context.BaseKey = "BaseKey";
             context.CachedResponseValidFor = TimeSpan.FromSeconds(10);
@@ -639,11 +707,12 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             var middleware = TestUtils.CreateTestMiddleware(testSink: sink, cache: cache);
             var context = TestUtils.CreateTestContext();
 
+            context.ShouldCacheResponse = true;
             middleware.ShimResponseStream(context);
             context.HttpContext.Response.ContentLength = 9;
+
             await context.HttpContext.Response.WriteAsync(new string('0', 10));
 
-            context.ShouldCacheResponse = true;
             context.CachedResponse = new CachedResponse();
             context.BaseKey = "BaseKey";
             context.CachedResponseValidFor = TimeSpan.FromSeconds(10);
@@ -664,10 +733,11 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             var middleware = TestUtils.CreateTestMiddleware(testSink: sink, cache: cache);
             var context = TestUtils.CreateTestContext();
 
+            context.ShouldCacheResponse = true;
             middleware.ShimResponseStream(context);
+
             await context.HttpContext.Response.WriteAsync(new string('0', 10));
 
-            context.ShouldCacheResponse = true;
             context.CachedResponse = new CachedResponse()
             {
                 Headers = new HeaderDictionary()
@@ -691,10 +761,10 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             var middleware = TestUtils.CreateTestMiddleware(testSink: sink, cache: cache);
             var context = TestUtils.CreateTestContext();
 
+            context.ShouldCacheResponse = false;
             middleware.ShimResponseStream(context);
             await context.HttpContext.Response.WriteAsync(new string('0', 10));
 
-            context.ShouldCacheResponse = false;
 
             await middleware.FinalizeCacheBodyAsync(context);
 
@@ -712,10 +782,10 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             var middleware = TestUtils.CreateTestMiddleware(testSink: sink, cache: cache);
             var context = TestUtils.CreateTestContext();
 
+            context.ShouldCacheResponse = true;
             middleware.ShimResponseStream(context);
             await context.HttpContext.Response.WriteAsync(new string('0', 10));
 
-            context.ShouldCacheResponse = true;
             context.ResponseCachingStream.DisableBuffering();
 
             await middleware.FinalizeCacheBodyAsync(context);
@@ -727,16 +797,52 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public void ShimResponseStream_SecondInvocation_Throws()
+        public void AddResponseCachingFeature_SecondInvocation_Throws()
         {
-            var middleware = TestUtils.CreateTestMiddleware();
+            var httpContext = new DefaultHttpContext();
-            var context = TestUtils.CreateTestContext();
 
             // Should not throw
-            middleware.ShimResponseStream(context);
+            ResponseCachingMiddleware.AddResponseCachingFeature(httpContext);
 
             // Should throw
-            Assert.ThrowsAny<InvalidOperationException>(() => middleware.ShimResponseStream(context));
+            Assert.ThrowsAny<InvalidOperationException>(() => ResponseCachingMiddleware.AddResponseCachingFeature(httpContext));
+        }
+
+        private class FakeResponseFeature : HttpResponseFeature
+        {
+            public override void OnStarting(Func<object, Task> callback, object state) { }
+        }
+
+        [Theory]
+        // If allowResponseCaching is false, other settings will not matter but are included for completeness
+        [InlineData(false, false, false)]
+        [InlineData(false, false, true)]
+        [InlineData(false, true, false)]
+        [InlineData(false, true, true)]
+        [InlineData(true, false, false)]
+        [InlineData(true, false, true)]
+        [InlineData(true, true, false)]
+        [InlineData(true, true, true)]
+        public async Task Invoke_AddsResponseCachingFeature_Always(bool allowResponseCaching, bool allowCacheLookup, bool allowCacheStorage)
+        {
+            var responseCachingFeatureAdded = false;
+            var middleware = TestUtils.CreateTestMiddleware(next: httpContext =>
+            {
+                responseCachingFeatureAdded = httpContext.Features.Get<IResponseCachingFeature>() != null;
+                return TaskCache.CompletedTask;
+            },
+            policyProvider: new TestResponseCachingPolicyProvider
+            {
+                AttemptResponseCachingValue = allowResponseCaching,
+                AllowCacheLookupValue = allowCacheLookup,
+                AllowCacheStorageValue = allowCacheStorage
+            });
+
+            var context = new DefaultHttpContext();
+            context.Features.Set<IHttpResponseFeature>(new FakeResponseFeature());
+            await middleware.Invoke(context);
+
+            Assert.True(responseCachingFeatureAdded);
         }
 
         [Fact]

test/Microsoft.AspNetCore.ResponseCaching.Tests/ResponseCachingPolicyProviderTests.cs

@@ -3,7 +3,6 @@
 
 using System;
 using Microsoft.AspNetCore.Http;
-using Microsoft.AspNetCore.Http.Headers;
 using Microsoft.AspNetCore.ResponseCaching.Internal;
 using Microsoft.Extensions.Logging.Testing;
 using Microsoft.Net.Http.Headers;
@@ -27,13 +26,13 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
 
         [Theory]
         [MemberData(nameof(CacheableMethods))]
-        public void IsRequestCacheable_CacheableMethods_Allowed(string method)
+        public void AttemptResponseCaching_CacheableMethods_Allowed(string method)
         {
             var sink = new TestSink();
             var context = TestUtils.CreateTestContext(sink);
             context.HttpContext.Request.Method = method;
 
-            Assert.True(new ResponseCachingPolicyProvider().IsRequestCacheable(context));
+            Assert.True(new ResponseCachingPolicyProvider().AttemptResponseCaching(context));
             Assert.Empty(sink.Writes);
         }
         public static TheoryData<string> NonCacheableMethods
@@ -56,51 +55,34 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
 
         [Theory]
         [MemberData(nameof(NonCacheableMethods))]
-        public void IsRequestCacheable_UncacheableMethods_NotAllowed(string method)
+        public void AttemptResponseCaching_UncacheableMethods_NotAllowed(string method)
         {
             var sink = new TestSink();
             var context = TestUtils.CreateTestContext(sink);
             context.HttpContext.Request.Method = method;
 
-            Assert.False(new ResponseCachingPolicyProvider().IsRequestCacheable(context));
+            Assert.False(new ResponseCachingPolicyProvider().AttemptResponseCaching(context));
             TestUtils.AssertLoggedMessages(
                 sink.Writes,
                 LoggedMessage.RequestMethodNotCacheable);
         }
 
         [Fact]
-        public void IsRequestCacheable_AuthorizationHeaders_NotAllowed()
+        public void AttemptResponseCaching_AuthorizationHeaders_NotAllowed()
         {
             var sink = new TestSink();
             var context = TestUtils.CreateTestContext(sink);
             context.HttpContext.Request.Method = HttpMethods.Get;
             context.HttpContext.Request.Headers[HeaderNames.Authorization] = "Basic plaintextUN:plaintextPW";
 
-            Assert.False(new ResponseCachingPolicyProvider().IsRequestCacheable(context));
+            Assert.False(new ResponseCachingPolicyProvider().AttemptResponseCaching(context));
             TestUtils.AssertLoggedMessages(
                 sink.Writes,
                 LoggedMessage.RequestWithAuthorizationNotCacheable);
         }
 
         [Fact]
-        public void IsRequestCacheable_NoCache_NotAllowed()
+        public void AllowCacheStorage_NoStore_Allowed()
-        {
-            var sink = new TestSink();
-            var context = TestUtils.CreateTestContext(sink);
-            context.HttpContext.Request.Method = HttpMethods.Get;
-            context.HttpContext.Request.Headers[HeaderNames.CacheControl] = new CacheControlHeaderValue()
-            {
-                NoCache = true
-            }.ToString();
-
-            Assert.False(new ResponseCachingPolicyProvider().IsRequestCacheable(context));
-            TestUtils.AssertLoggedMessages(
-                sink.Writes,
-                LoggedMessage.RequestWithNoCacheNotCacheable);
-        }
-
-        [Fact]
-        public void IsRequestCacheable_NoStore_Allowed()
         {
             var sink = new TestSink();
             var context = TestUtils.CreateTestContext(sink);
@@ -110,26 +92,43 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
                 NoStore = true
             }.ToString();
 
-            Assert.True(new ResponseCachingPolicyProvider().IsRequestCacheable(context));
+            Assert.True(new ResponseCachingPolicyProvider().AllowCacheLookup(context));
             Assert.Empty(sink.Writes);
         }
 
         [Fact]
-        public void IsRequestCacheable_LegacyDirectives_NotAllowed()
+        public void AllowCacheLookup_NoCache_NotAllowed()
+        {
+            var sink = new TestSink();
+            var context = TestUtils.CreateTestContext(sink);
+            context.HttpContext.Request.Method = HttpMethods.Get;
+            context.HttpContext.Request.Headers[HeaderNames.CacheControl] = new CacheControlHeaderValue()
+            {
+                NoCache = true
+            }.ToString();
+
+            Assert.False(new ResponseCachingPolicyProvider().AllowCacheLookup(context));
+            TestUtils.AssertLoggedMessages(
+                sink.Writes,
+                LoggedMessage.RequestWithNoCacheNotCacheable);
+        }
+
+        [Fact]
+        public void AllowCacheLookup_LegacyDirectives_NotAllowed()
         {
             var sink = new TestSink();
             var context = TestUtils.CreateTestContext(sink);
             context.HttpContext.Request.Method = HttpMethods.Get;
             context.HttpContext.Request.Headers[HeaderNames.Pragma] = "no-cache";
 
-            Assert.False(new ResponseCachingPolicyProvider().IsRequestCacheable(context));
+            Assert.False(new ResponseCachingPolicyProvider().AllowCacheLookup(context));
             TestUtils.AssertLoggedMessages(
                 sink.Writes,
                 LoggedMessage.RequestWithPragmaNoCacheNotCacheable);
         }
 
         [Fact]
-        public void IsRequestCacheable_LegacyDirectives_OverridenByCacheControl()
+        public void AllowCacheLookup_LegacyDirectives_OverridenByCacheControl()
         {
             var sink = new TestSink();
             var context = TestUtils.CreateTestContext(sink);
@@ -137,7 +136,22 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             context.HttpContext.Request.Headers[HeaderNames.Pragma] = "no-cache";
             context.HttpContext.Request.Headers[HeaderNames.CacheControl] = "max-age=10";
 
-            Assert.True(new ResponseCachingPolicyProvider().IsRequestCacheable(context));
+            Assert.True(new ResponseCachingPolicyProvider().AllowCacheLookup(context));
+            Assert.Empty(sink.Writes);
+        }
+
+        [Fact]
+        public void AllowCacheStorage_NoStore_NotAllowed()
+        {
+            var sink = new TestSink();
+            var context = TestUtils.CreateTestContext(sink);
+            context.HttpContext.Request.Method = HttpMethods.Get;
+            context.HttpContext.Request.Headers[HeaderNames.CacheControl] = new CacheControlHeaderValue()
+            {
+                NoStore = true
+            }.ToString();
+
+            Assert.False(new ResponseCachingPolicyProvider().AllowCacheStorage(context));
             Assert.Empty(sink.Writes);
         }
 
@@ -184,26 +198,6 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
                 LoggedMessage.ResponseWithNoCacheNotCacheable);
         }
 
-        [Fact]
-        public void IsResponseCacheable_RequestNoStore_NotAllowed()
-        {
-            var sink = new TestSink();
-            var context = TestUtils.CreateTestContext(sink);
-            context.HttpContext.Request.Headers[HeaderNames.CacheControl] = new CacheControlHeaderValue()
-            {
-                NoStore = true
-            }.ToString();
-            context.HttpContext.Response.Headers[HeaderNames.CacheControl] = new CacheControlHeaderValue()
-            {
-                Public = true
-            }.ToString();
-
-            Assert.False(new ResponseCachingPolicyProvider().IsResponseCacheable(context));
-            TestUtils.AssertLoggedMessages(
-                sink.Writes,
-                LoggedMessage.ResponseWithNoStoreNotCacheable);
-        }
-
         [Fact]
         public void IsResponseCacheable_ResponseNoStore_NotAllowed()
         {
@@ -289,6 +283,9 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Theory]
+        [InlineData(StatusCodes.Status100Continue)]
+        [InlineData(StatusCodes.Status101SwitchingProtocols)]
+        [InlineData(StatusCodes.Status102Processing)]
         [InlineData(StatusCodes.Status201Created)]
         [InlineData(StatusCodes.Status202Accepted)]
         [InlineData(StatusCodes.Status203NonAuthoritative)]
@@ -296,6 +293,8 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         [InlineData(StatusCodes.Status205ResetContent)]
         [InlineData(StatusCodes.Status206PartialContent)]
         [InlineData(StatusCodes.Status207MultiStatus)]
+        [InlineData(StatusCodes.Status208AlreadyReported)]
+        [InlineData(StatusCodes.Status226IMUsed)]
         [InlineData(StatusCodes.Status300MultipleChoices)]
         [InlineData(StatusCodes.Status301MovedPermanently)]
         [InlineData(StatusCodes.Status302Found)]
@@ -325,9 +324,14 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         [InlineData(StatusCodes.Status417ExpectationFailed)]
         [InlineData(StatusCodes.Status418ImATeapot)]
         [InlineData(StatusCodes.Status419AuthenticationTimeout)]
+        [InlineData(StatusCodes.Status421MisdirectedRequest)]
         [InlineData(StatusCodes.Status422UnprocessableEntity)]
         [InlineData(StatusCodes.Status423Locked)]
         [InlineData(StatusCodes.Status424FailedDependency)]
+        [InlineData(StatusCodes.Status426UpgradeRequired)]
+        [InlineData(StatusCodes.Status428PreconditionRequired)]
+        [InlineData(StatusCodes.Status429TooManyRequests)]
+        [InlineData(StatusCodes.Status431RequestHeaderFieldsTooLarge)]
         [InlineData(StatusCodes.Status451UnavailableForLegalReasons)]
         [InlineData(StatusCodes.Status500InternalServerError)]
         [InlineData(StatusCodes.Status501NotImplemented)]
@@ -337,6 +341,9 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         [InlineData(StatusCodes.Status505HttpVersionNotsupported)]
         [InlineData(StatusCodes.Status506VariantAlsoNegotiates)]
         [InlineData(StatusCodes.Status507InsufficientStorage)]
+        [InlineData(StatusCodes.Status508LoopDetected)]
+        [InlineData(StatusCodes.Status510NotExtended)]
+        [InlineData(StatusCodes.Status511NetworkAuthenticationRequired)]
         public void IsResponseCacheable_NonSuccessStatusCodes_NotAllowed(int statusCode)
         {
             var sink = new TestSink();
@@ -687,6 +694,29 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
                 LoggedMessage.ExpirationMaxStaleSatisfied);
         }
 
+        [Fact]
+        public void IsCachedEntryFresh_MaxStaleInfiniteOverridesFreshness_ToFresh()
+        {
+            var sink = new TestSink();
+            var context = TestUtils.CreateTestContext(sink);
+            context.HttpContext.Request.Headers[HeaderNames.CacheControl] = new CacheControlHeaderValue()
+            {
+                MaxAge = TimeSpan.FromSeconds(5),
+                MaxStale = true // No value specified means a MaxStaleLimit of infinity
+            }.ToString();
+            context.CachedResponseHeaders = new HeaderDictionary();
+            context.CachedResponseHeaders[HeaderNames.CacheControl] = new CacheControlHeaderValue()
+            {
+                MaxAge = TimeSpan.FromSeconds(5),
+            }.ToString();
+            context.CachedEntryAge = TimeSpan.FromSeconds(6);
+
+            Assert.True(new ResponseCachingPolicyProvider().IsCachedEntryFresh(context));
+            TestUtils.AssertLoggedMessages(
+                sink.Writes,
+                LoggedMessage.ExpirationInfiniteMaxStaleSatisfied);
+        }
+
         [Fact]
         public void IsCachedEntryFresh_MaxStaleOverridesFreshness_ButStillNotFresh()
         {
@@ -735,5 +765,30 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
                 sink.Writes,
                 LoggedMessage.ExpirationMustRevalidate);
         }
+
+        [Fact]
+        public void IsCachedEntryFresh_ProxyRevalidateOverridesRequestMaxStale_ToNotFresh()
+        {
+            var sink = new TestSink();
+            var context = TestUtils.CreateTestContext(sink);
+            context.HttpContext.Request.Headers[HeaderNames.CacheControl] = new CacheControlHeaderValue()
+            {
+                MaxAge = TimeSpan.FromSeconds(5),
+                MaxStale = true, // This value must be set to true in order to specify MaxStaleLimit
+                MaxStaleLimit = TimeSpan.FromSeconds(2)
+            }.ToString();
+            context.CachedResponseHeaders = new HeaderDictionary();
+            context.CachedResponseHeaders[HeaderNames.CacheControl] = new CacheControlHeaderValue()
+            {
+                MaxAge = TimeSpan.FromSeconds(5),
+                MustRevalidate = true
+            }.ToString();
+            context.CachedEntryAge = TimeSpan.FromSeconds(6);
+
+            Assert.False(new ResponseCachingPolicyProvider().IsCachedEntryFresh(context));
+            TestUtils.AssertLoggedMessages(
+                sink.Writes,
+                LoggedMessage.ExpirationMustRevalidate);
+        }
     }
 }

test/Microsoft.AspNetCore.ResponseCaching.Tests/ResponseCachingTests.cs

@@ -123,10 +123,16 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
                 using (var server = new TestServer(builder))
                 {
                     var client = server.CreateClient();
-                    client.DefaultRequestHeaders.CacheControl =
-                        new System.Net.Http.Headers.CacheControlHeaderValue { NoCache = true };
 
                     var initialResponse = await client.SendAsync(TestUtils.CreateRequest(method, ""));
+
+                    // verify the response is cached
+                    var cachedResponse = await client.SendAsync(TestUtils.CreateRequest(method, ""));
+                    await AssertCachedResponseAsync(initialResponse, cachedResponse);
+
+                    // assert cached response no longer served
+                    client.DefaultRequestHeaders.CacheControl =
+                        new System.Net.Http.Headers.CacheControlHeaderValue { NoCache = true };
                     var subsequentResponse = await client.SendAsync(TestUtils.CreateRequest(method, ""));
 
                     await AssertFreshResponseAsync(initialResponse, subsequentResponse);
@@ -146,10 +152,16 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
                 using (var server = new TestServer(builder))
                 {
                     var client = server.CreateClient();
-                    client.DefaultRequestHeaders.Pragma.Clear();
-                    client.DefaultRequestHeaders.Pragma.Add(new System.Net.Http.Headers.NameValueHeaderValue("no-cache"));
 
                     var initialResponse = await client.SendAsync(TestUtils.CreateRequest(method, ""));
+
+                    // verify the response is cached
+                    var cachedResponse = await client.SendAsync(TestUtils.CreateRequest(method, ""));
+                    await AssertCachedResponseAsync(initialResponse, cachedResponse);
+
+                    // assert cached response no longer served
+                    client.DefaultRequestHeaders.Pragma.Clear();
+                    client.DefaultRequestHeaders.Pragma.Add(new System.Net.Http.Headers.NameValueHeaderValue("no-cache"));
                     var subsequentResponse = await client.SendAsync(TestUtils.CreateRequest(method, ""));
 
                     await AssertFreshResponseAsync(initialResponse, subsequentResponse);
@@ -565,7 +577,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public async void ServesCachedContent_IfSubsequentRequest_ContainsNoStore()
+        public async void ServesCachedContent_IfSubsequentRequestContainsNoStore()
         {
             var builders = TestUtils.CreateBuildersWithResponseCaching();
 
@@ -587,7 +599,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         [Fact]
-        public async void ServesFreshContent_IfInitialRequestContains_NoStore()
+        public async void ServesFreshContent_IfInitialRequestContainsNoStore()
         {
             var builders = TestUtils.CreateBuildersWithResponseCaching();
 
@@ -608,6 +620,31 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             }
         }
 
+        [Fact]
+        public async void ServesFreshContent_IfInitialResponseContainsNoStore()
+        {
+            var builders = TestUtils.CreateBuildersWithResponseCaching(requestDelegate: async (context) =>
+            {
+                var headers = context.Response.GetTypedHeaders().CacheControl = new CacheControlHeaderValue()
+                {
+                    NoStore = true
+                };
+                await TestUtils.TestRequestDelegate(context);
+            });
+
+            foreach (var builder in builders)
+            {
+                using (var server = new TestServer(builder))
+                {
+                    var client = server.CreateClient();
+                    var initialResponse = await client.GetAsync("");
+                    var subsequentResponse = await client.GetAsync("");
+
+                    await AssertFreshResponseAsync(initialResponse, subsequentResponse);
+                }
+            }
+        }
+
         [Fact]
         public async void Serves304_IfIfModifiedSince_Satisfied()
         {
@@ -619,7 +656,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
                 {
                     var client = server.CreateClient();
                     var initialResponse = await client.GetAsync("");
-                    client.DefaultRequestHeaders.IfUnmodifiedSince = DateTimeOffset.MaxValue;
+                    client.DefaultRequestHeaders.IfModifiedSince = DateTimeOffset.MaxValue;
                     var subsequentResponse = await client.GetAsync("");
 
                     initialResponse.EnsureSuccessStatusCode();
@@ -639,7 +676,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
                 {
                     var client = server.CreateClient();
                     var initialResponse = await client.GetAsync("");
-                    client.DefaultRequestHeaders.IfUnmodifiedSince = DateTimeOffset.MinValue;
+                    client.DefaultRequestHeaders.IfModifiedSince = DateTimeOffset.MinValue;
                     var subsequentResponse = await client.GetAsync("");
 
                     await AssertCachedResponseAsync(initialResponse, subsequentResponse);

test/Microsoft.AspNetCore.ResponseCaching.Tests/TestUtils.cs

@@ -20,6 +20,7 @@ using Microsoft.Extensions.Options;
 using Microsoft.Extensions.Primitives;
 using Microsoft.Net.Http.Headers;
 using Xunit;
+using ISystemClock = Microsoft.AspNetCore.ResponseCaching.Internal.ISystemClock;
 
 namespace Microsoft.AspNetCore.ResponseCaching.Tests
 {
@@ -42,11 +43,19 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             }
 
             var uniqueId = Guid.NewGuid().ToString();
-            headers.CacheControl = new CacheControlHeaderValue
+            if (headers.CacheControl == null)
             {
-                Public = true,
+                headers.CacheControl = new CacheControlHeaderValue
-                MaxAge = string.IsNullOrEmpty(expires) ? TimeSpan.FromSeconds(10) : (TimeSpan?)null
+                {
-            };
+                    Public = true,
+                    MaxAge = string.IsNullOrEmpty(expires) ? TimeSpan.FromSeconds(10) : (TimeSpan?)null
+                };
+            }
+            else
+            {
+                headers.CacheControl.Public = true;
+                headers.CacheControl.MaxAge = string.IsNullOrEmpty(expires) ? TimeSpan.FromSeconds(10) : (TimeSpan?)null;
+            }
             headers.Date = DateTimeOffset.UtcNow;
             headers.Headers["X-Value"] = uniqueId;
 
@@ -103,12 +112,17 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         }
 
         internal static ResponseCachingMiddleware CreateTestMiddleware(
+            RequestDelegate next = null,
             IResponseCache cache = null,
             ResponseCachingOptions options = null,
             TestSink testSink = null,
             IResponseCachingKeyProvider keyProvider = null,
             IResponseCachingPolicyProvider policyProvider = null)
         {
+            if (next == null)
+            {
+                next = httpContext => TaskCache.CompletedTask;
+            }
             if (cache == null)
             {
                 cache = new TestResponseCache();
@@ -127,7 +141,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             }
 
             return new ResponseCachingMiddleware(
-                httpContext => TaskCache.CompletedTask,
+                next,
                 Options.Create(options),
                 testSink == null ? (ILoggerFactory)NullLoggerFactory.Instance : new TestLoggerFactory(testSink, true),
                 policyProvider,
@@ -188,7 +202,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         internal static LoggedMessage ResponseWithUnsuccessfulStatusCodeNotCacheable => new LoggedMessage(17, LogLevel.Debug);
         internal static LoggedMessage NotModifiedIfNoneMatchStar => new LoggedMessage(18, LogLevel.Debug);
         internal static LoggedMessage NotModifiedIfNoneMatchMatched => new LoggedMessage(19, LogLevel.Debug);
-        internal static LoggedMessage NotModifiedIfUnmodifiedSinceSatisfied => new LoggedMessage(20, LogLevel.Debug);
+        internal static LoggedMessage NotModifiedIfModifiedSinceSatisfied => new LoggedMessage(20, LogLevel.Debug);
         internal static LoggedMessage NotModifiedServed => new LoggedMessage(21, LogLevel.Information);
         internal static LoggedMessage CachedResponseServed => new LoggedMessage(22, LogLevel.Information);
         internal static LoggedMessage GatewayTimeoutServed => new LoggedMessage(23, LogLevel.Information);
@@ -197,6 +211,7 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
         internal static LoggedMessage ResponseCached => new LoggedMessage(26, LogLevel.Information);
         internal static LoggedMessage ResponseNotCached => new LoggedMessage(27, LogLevel.Information);
         internal static LoggedMessage ResponseContentLengthMismatchNotCached => new LoggedMessage(28, LogLevel.Warning);
+        internal static LoggedMessage ExpirationInfiniteMaxStaleSatisfied => new LoggedMessage(29, LogLevel.Debug);
 
         private LoggedMessage(int evenId, LogLevel logLevel)
         {
@@ -218,11 +233,21 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
 
     internal class TestResponseCachingPolicyProvider : IResponseCachingPolicyProvider
     {
-        public bool IsCachedEntryFresh(ResponseCachingContext context) => true;
+        public bool AllowCacheLookupValue { get; set; } = false;
+        public bool AllowCacheStorageValue { get; set; } = false;
+        public bool AttemptResponseCachingValue { get; set; } = false;
+        public bool IsCachedEntryFreshValue { get; set; } = true;
+        public bool IsResponseCacheableValue { get; set; } = true;
 
-        public bool IsRequestCacheable(ResponseCachingContext context) => true;
+        public bool AllowCacheLookup(ResponseCachingContext context) => AllowCacheLookupValue;
 
-        public bool IsResponseCacheable(ResponseCachingContext context) => true;
+        public bool AllowCacheStorage(ResponseCachingContext context) => AllowCacheStorageValue;
+
+        public bool AttemptResponseCaching(ResponseCachingContext context) => AttemptResponseCachingValue;
+
+        public bool IsCachedEntryFresh(ResponseCachingContext context) => IsCachedEntryFreshValue;
+
+        public bool IsResponseCacheable(ResponseCachingContext context) => IsResponseCacheableValue;
     }
 
     internal class TestResponseCachingKeyProvider : IResponseCachingKeyProvider
@@ -284,4 +309,9 @@ namespace Microsoft.AspNetCore.ResponseCaching.Tests
             return TaskCache.CompletedTask;
         }
     }
+
+    internal class TestClock : ISystemClock
+    {
+        public DateTimeOffset UtcNow { get; set; }
+    }
 }