[core] Rationalize error handling for resource loading

* Standardize on std::exception_ptr as the error representation
  (fixes #2854).
* Don't format textual strings at the error source; pass on the
  constituent data via observer method parameters instead.
* Use the null object pattern to simplify observer notification code.
* Further refactoring for ResourceLoading tests.

1 files changed, 7 insertions, 19 deletions

diff --git a/src/mbgl/text/glyph_pbf.hpp b/src/mbgl/text/glyph_pbf.hpp
index d595298516..e0f65e7789 100644
--- a/src/mbgl/text/glyph_pbf.hpp
+++ b/src/mbgl/text/glyph_pbf.hpp
@@ -2,6 +2,7 @@
 #define MBGL_TEXT_GLYPH_PBF
 
 #include <mbgl/text/glyph.hpp>
+#include <mbgl/text/glyph_store.hpp>
 #include <mbgl/util/noncopyable.hpp>
 
 #include <atomic>
@@ -11,43 +12,30 @@
 
 namespace mbgl {
 
-class GlyphStore;
 class FontStack;
 class FileRequest;
 
 class GlyphPBF : private util::noncopyable {
 public:
-    class Observer {
-    public:
-        virtual ~Observer() = default;
-
-        virtual void onGlyphPBFLoaded() = 0;
-        virtual void onGlyphPBFLoadingFailed(std::exception_ptr error) = 0;
-    };
-
     GlyphPBF(GlyphStore* store,
              const std::string& fontStack,
-             const GlyphRange& glyphRange);
-    virtual ~GlyphPBF();
+             const GlyphRange&,
+             GlyphStore::Observer*);
+    ~GlyphPBF();
 
     bool isParsed() const {
         return parsed;
-    };
-
-    void setObserver(Observer* observer);
+    }
 
 private:
-    void emitGlyphPBFLoaded();
-    void emitGlyphPBFLoadingFailed(const std::string& message);
-
-    void parse(GlyphStore* store, const std::string& fontStack, const std::string& url);
+    void parse(GlyphStore*, const std::string& fontStack, const GlyphRange&);
 
     std::shared_ptr<const std::string> data;
     std::atomic<bool> parsed;
 
     std::unique_ptr<FileRequest> req;
 
-    Observer* observer = nullptr;
+    GlyphStore::Observer* observer = nullptr;
 };
 
 } // namespace mbgl