2 files changed, 11 insertions, 0 deletions
diff --git a/include/mbgl/storage/resource.hpp b/include/mbgl/storage/resource.hpp
index 7e9ced8049..5d44f4869f 100644
--- a/include/mbgl/storage/resource.hpp
+++ b/include/mbgl/storage/resource.hpp
@@ -68,6 +68,7 @@ public:
     optional<Timestamp> priorModified = {};
     optional<Timestamp> priorExpires = {};
     optional<std::string> priorEtag = {};
+    std::shared_ptr<const std::string> priorData;
 };
 
 } // namespace mbgl
diff --git a/include/mbgl/storage/response.hpp b/include/mbgl/storage/response.hpp
index 32fe4e0c8a..711f008e83 100644
--- a/include/mbgl/storage/response.hpp
+++ b/include/mbgl/storage/response.hpp
@@ -27,6 +27,10 @@ public:
     // This is set to true for 304 Not Modified responses.
     bool notModified = false;
 
+    // This is set to true when the server requested that no expired resources be used by
+    // specifying "Cache-Control: must-revalidate".
+    bool mustRevalidate = false;
+
     // The actual data of the response. Present only for non-error, non-notModified responses.
     std::shared_ptr<const std::string> data;
 
@@ -37,6 +41,12 @@ public:
     bool isFresh() const {
         return expires ? *expires > util::now() : !error;
     }
+
+    // Indicates whether we are allowed to use this response according to HTTP caching rules.
+    // It may or may not be stale.
+    bool isUsable() const {
+        return !mustRevalidate || (expires && *expires > util::now());
+    }
 };
 
 class Response::Error {