[core] make forcing cache/network only more explicit

Previously, we used the existence of a `prior*` field in the Resource object as an indication for whether we should consult the cache or not. However, this is prone to error, since a failed cache lookup won't set any prior fields. Therefore, we manually set `priorExpires` to 0. This in turn triggered another bug where generated wrong expiration timestamps when the server response we got was expired (or expired between sending and receiving).

This commit changes the flags so that we can now explicitly request CacheOnly/NetworkOnly (or All) loading methods, rather than the implicit Optional/Required naming scheme.

1 files changed, 36 insertions, 7 deletions

diff --git a/include/mbgl/storage/resource.hpp b/include/mbgl/storage/resource.hpp
index 5d44f4869f..318fa389f4 100644
--- a/include/mbgl/storage/resource.hpp
+++ b/include/mbgl/storage/resource.hpp
@@ -4,6 +4,8 @@
 #include <mbgl/util/optional.hpp>
 #include <mbgl/util/font_stack.hpp>
 #include <mbgl/util/tileset.hpp>
+#include <mbgl/util/util.hpp>
+#include <mbgl/util/traits.hpp>
 
 #include <string>
 
@@ -30,18 +32,28 @@ public:
         int8_t z;
     };
 
-    enum Necessity : bool {
-        Optional = false,
-        Required = true,
+    enum class LoadingMethod : uint8_t {
+        None        = 0b00,
+        Cache       = 0b01,
+        Network     = 0b10,
+
+        CacheOnly   = Cache,
+        NetworkOnly = Network,
+        All         = Cache | Network,
     };
 
-    Resource(Kind kind_, std::string url_, optional<TileData> tileData_ = {}, Necessity necessity_ = Required)
+    Resource(Kind kind_,
+             std::string url_,
+             optional<TileData> tileData_ = {},
+             LoadingMethod loadingMethod_ = LoadingMethod::All)
         : kind(kind_),
-          necessity(necessity_),
+          loadingMethod(loadingMethod_),
           url(std::move(url_)),
           tileData(std::move(tileData_)) {
     }
 
+    bool hasLoadingMethod(LoadingMethod method);
+
     static Resource style(const std::string& url);
     static Resource source(const std::string& url);
     static Resource tile(const std::string& urlTemplate,
@@ -50,7 +62,7 @@ public:
                          int32_t y,
                          int8_t z,
                          Tileset::Scheme scheme,
-                         Necessity = Required);
+                         LoadingMethod = LoadingMethod::All);
     static Resource glyphs(const std::string& urlTemplate,
                            const FontStack& fontStack,
                            const std::pair<uint16_t, uint16_t>& glyphRange);
@@ -59,7 +71,7 @@ public:
     static Resource image(const std::string& url);
     
     Kind kind;
-    Necessity necessity;
+    LoadingMethod loadingMethod;
     std::string url;
 
     // Includes auxiliary data if this is a tile request.
@@ -71,4 +83,21 @@ public:
     std::shared_ptr<const std::string> priorData;
 };
 
+
+MBGL_CONSTEXPR Resource::LoadingMethod operator|(Resource::LoadingMethod a, Resource::LoadingMethod b) {
+    return Resource::LoadingMethod(mbgl::underlying_type(a) | mbgl::underlying_type(b));
+}
+
+MBGL_CONSTEXPR Resource::LoadingMethod& operator|=(Resource::LoadingMethod& a, Resource::LoadingMethod b) {
+    return (a = a | b);
+}
+
+MBGL_CONSTEXPR Resource::LoadingMethod operator&(Resource::LoadingMethod a, Resource::LoadingMethod b) {
+    return Resource::LoadingMethod(mbgl::underlying_type(a) & mbgl::underlying_type(b));
+}
+
+inline bool Resource::hasLoadingMethod(Resource::LoadingMethod method) {
+    return (loadingMethod & method) != Resource::LoadingMethod::None;
+}
+
 } // namespace mbgl