[core] only perform optional requests if the FileSource supports it

2 files changed, 12 insertions, 0 deletions

diff --git a/include/mbgl/storage/default_file_source.hpp b/include/mbgl/storage/default_file_source.hpp
index e77befda1b..235e738254 100644
--- a/include/mbgl/storage/default_file_source.hpp
+++ b/include/mbgl/storage/default_file_source.hpp
@@ -26,6 +26,10 @@ public:
                       uint64_t maximumCacheSize = util::DEFAULT_MAX_CACHE_SIZE);
     ~DefaultFileSource() override;
 
+    bool supportsOptionalRequests() const override {
+        return true;
+    }
+
     void setAccessToken(const std::string&);
     std::string getAccessToken() const;
 
diff --git a/include/mbgl/storage/file_source.hpp b/include/mbgl/storage/file_source.hpp
index 88e0336187..404c683fdb 100644
--- a/include/mbgl/storage/file_source.hpp
+++ b/include/mbgl/storage/file_source.hpp
@@ -23,6 +23,14 @@ public:
     // If the request is cancelled before the callback is executed, the callback will
     // not be executed.
     virtual std::unique_ptr<AsyncRequest> request(const Resource&, Callback) = 0;
+
+    // When a file source supports optional requests, it must return true.
+    // Optional requests are requests that aren't as urgent, but could be useful, e.g.
+    // to cover part of the map while loading. The FileSource should only do cheap actions to
+    // retrieve the data, e.g. load it from a cache, but not from the internet.
+    virtual bool supportsOptionalRequests() const {
+        return false;
+    }
 };
 
 } // namespace mbgl