From c19f3d29ca8fd1b8359940b52faf4c32d2b0b601 Mon Sep 17 00:00:00 2001
From: Martin Costello <martin@martincostello.com>
Date: Wed, 24 Jun 2020 23:48:36 +0100
Subject: [PATCH] Only look-up Cache-Control once (#23329)

Only look-up the Cache-Control header once, rather than twice if non-empty.
---
 .../ResponseCaching/src/ResponseCachingPolicyProvider.cs     | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/Middleware/ResponseCaching/src/ResponseCachingPolicyProvider.cs b/src/Middleware/ResponseCaching/src/ResponseCachingPolicyProvider.cs
index 3cb94ab005..491d803d94 100644
--- a/src/Middleware/ResponseCaching/src/ResponseCachingPolicyProvider.cs
+++ b/src/Middleware/ResponseCaching/src/ResponseCachingPolicyProvider.cs
@@ -34,11 +34,12 @@ namespace Microsoft.AspNetCore.ResponseCaching
         public virtual bool AllowCacheLookup(ResponseCachingContext context)
         {
             var requestHeaders = context.HttpContext.Request.Headers;
+            var cacheControl = requestHeaders[HeaderNames.CacheControl];
 
             // Verify request cache-control parameters
-            if (!StringValues.IsNullOrEmpty(requestHeaders[HeaderNames.CacheControl]))
+            if (!StringValues.IsNullOrEmpty(cacheControl))
             {
-                if (HeaderUtilities.ContainsCacheDirective(requestHeaders[HeaderNames.CacheControl], CacheControlHeaderValue.NoCacheString))
+                if (HeaderUtilities.ContainsCacheDirective(cacheControl, CacheControlHeaderValue.NoCacheString))
                 {
                     context.Logger.RequestWithNoCacheNotCacheable();
                     return false;