Better control of caching logic by following headers and a manual option to turn of caching for a request

HttpClient.Caching/InMemory/InMemoryCacheHandler.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Net;
 using System.Net.Http;
+using System.Net.Http.Headers;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.Extensions.Caching.Abstractions;
@@ -14,7 +15,27 @@ namespace Microsoft.Extensions.Caching.InMemory
     /// </summary>
     public class InMemoryCacheHandler : DelegatingHandler
     {
-        private static HashSet<HttpMethod> CachedHttpMethods = new HashSet<HttpMethod>
+#if NET5_0_OR_GREATER
+        /// <summary>
+        ///   The key to use to store the UseCache value in the HttpRequestMessage.Options dictionary.
+        ///   This key is used to determine if the cache should be checked for the request.
+        ///   If the key is not present, the cache will be checked.
+        ///   If the key is present and the value is false, the cache will not be checked.
+        ///   If the key is present and the value is true, the cache will be checked.
+        /// </summary>
+        public static readonly HttpRequestOptionsKey<bool> UseCache = new HttpRequestOptionsKey<bool>(nameof(UseCache));
+#else
+        /// <summary>
+        ///   The key to use to store the UseCache value in the HttpRequestMessage.Properties dictionary.
+        ///   This key is used to determine if the cache should be checked for the request.
+        ///   If the key is not present, the cache will be checked.
+        ///   If the key is present and the value is false, the cache will not be checked.
+        ///   If the key is present and the value is true, the cache will be checked.
+        /// </summary>
+        public const string UseCache = nameof(UseCache);
+#endif
+
+        private static readonly HashSet<HttpMethod> CachedHttpMethods = new HashSet<HttpMethod>
         {
             HttpMethod.Get,
             HttpMethod.Head
@@ -50,10 +71,10 @@ public InMemoryCacheHandler(HttpMessageHandler innerHandler = null,
             IStatsProvider statsProvider = null,
             ICacheKeysProvider cacheKeysProvider = null)
             : this(innerHandler,
-                   cacheExpirationPerHttpResponseCode,
-                   statsProvider,
-                   new MemoryCache(new MemoryCacheOptions()),
-                   cacheKeysProvider)
+                cacheExpirationPerHttpResponseCode,
+                statsProvider,
+                new MemoryCache(new MemoryCacheOptions()),
+                cacheKeysProvider)
         {
         }
 
@@ -104,6 +125,40 @@ public void InvalidateCache(Uri uri, HttpMethod httpMethod = null)
             }
         }
 
+        /// <summary>
+        ///    Determines if the cache should be checked for the request.
+        /// </summary>
+        /// <param name="request"></param>
+        /// <returns>A bool representing if the cache should be cached or not</returns>
+        private static bool ShouldTheCacheBeChecked(HttpRequestMessage request)
+        {
+#if NET5_0_OR_GREATER
+            var useCacheOption = request.Options.TryGetValue(UseCache, out var useCache) == false || useCache == true;
+#else
+            var useCacheOption = request.Properties.TryGetValue(UseCache, out var useCache) == false || (bool)useCache == true;
+#endif
+
+            return useCacheOption && request.Headers.CacheControl?.NoCache != true;
+        }
+
+        /// <summary>
+        ///    Determines if the response should be cached.
+        /// </summary>
+        /// <param name="response"></param>
+        /// <returns>A bool representing if the response should be cached or not</returns>
+        private static bool ShouldCacheResponse(HttpResponseMessage response)
+        {
+            if (response.Headers.CacheControl is CacheControlHeaderValue cacheControl)
+            {
+                return
+                    cacheControl.NoStore == false &&
+                    cacheControl.NoCache == false &&
+                    response.StatusCode != HttpStatusCode.NotModified;
+            }
+
+            return response.StatusCode != HttpStatusCode.NotModified;
+        }
+
         /// <summary>
         ///     Tries to get the value from the cache, and only calls the delegating handler on cache misses.
         /// </summary>
@@ -114,7 +169,10 @@ protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage
 
             // Gets the data from cache, and returns the data if it's a cache hit
             var isCachedHttpMethod = CachedHttpMethods.Contains(request.Method);
-            if (isCachedHttpMethod)
+
+            // Check if the cache should be checked
+            var shouldCheckCache = ShouldTheCacheBeChecked(request);
+            if (shouldCheckCache && isCachedHttpMethod)
             {
                 key = this.CacheKeysProvider.GetKey(request);
 
@@ -131,13 +189,17 @@ protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage
             if (isCachedHttpMethod)
             {
                 var absoluteExpirationRelativeToNow = response.StatusCode.GetAbsoluteExpirationRelativeToNow(this.cacheExpirationPerHttpResponseCode);
+                var maxAgeHeader = response.Headers.CacheControl?.MaxAge ?? TimeSpan.MaxValue;
+
+                // If the server sends a Cache-Control header with a max-age that is less than the configured expiration time, use the max-age value
+                var maxCacheTime = (maxAgeHeader < absoluteExpirationRelativeToNow) ? maxAgeHeader : absoluteExpirationRelativeToNow;
 
                 this.StatsProvider.ReportCacheMiss(response.StatusCode);
 
-                if (TimeSpan.Zero != absoluteExpirationRelativeToNow)
+                if (ShouldCacheResponse(response) && TimeSpan.Zero != maxCacheTime)
                 {
                     var entry = await response.ToCacheEntryAsync();
-                    await this.responseCache.TrySetAsync(key, entry, absoluteExpirationRelativeToNow);
+                    await this.responseCache.TrySetAsync(key, entry, maxCacheTime);
                     return request.PrepareCachedEntry(entry);
                 }
             }
@@ -153,7 +215,10 @@ protected override HttpResponseMessage Send(HttpRequestMessage request, Cancella
 
             // Gets the data from cache, and returns the data if it's a cache hit
             var isCachedHttpMethod = CachedHttpMethods.Contains(request.Method);
-            if (isCachedHttpMethod)
+
+            // Check if the cache should be checked
+            var shouldCheckCache = ShouldTheCacheBeChecked(request);
+            if (shouldCheckCache && isCachedHttpMethod)
             {
                 key = this.CacheKeysProvider.GetKey(request);
 
@@ -169,13 +234,17 @@ protected override HttpResponseMessage Send(HttpRequestMessage request, Cancella
             if (isCachedHttpMethod)
             {
                 var absoluteExpirationRelativeToNow = response.StatusCode.GetAbsoluteExpirationRelativeToNow(this.cacheExpirationPerHttpResponseCode);
+                var maxAgeHeader = response.Headers.CacheControl?.MaxAge ?? TimeSpan.MaxValue;
+
+                // If the server sends a Cache-Control header with a max-age that is less than the configured expiration time, use the max-age value
+                var maxCacheTime = (maxAgeHeader < absoluteExpirationRelativeToNow) ? maxAgeHeader : absoluteExpirationRelativeToNow;
 
                 this.StatsProvider.ReportCacheMiss(response.StatusCode);
 
-                if (TimeSpan.Zero != absoluteExpirationRelativeToNow)
+                if (ShouldCacheResponse(response) && TimeSpan.Zero != maxCacheTime)
                 {
                     var cacheData = response.ToCacheEntry();
-                    this.responseCache.TrySetCacheData(key, cacheData, absoluteExpirationRelativeToNow);
+                    this.responseCache.TrySetCacheData(key, cacheData, maxCacheTime);
                     return request.PrepareCachedEntry(cacheData);
                 }
             }