[core, android] Factor JSON string conversions

This adds a `convertJSON` template, to be used like:

   Error error
   optional<Foo> foo = convertJSON<Foo>(string, error);

Internally, it parses the string with RapidJSON and then calls `convert<Foo>(parsed, error)`.

While here, rationalize GeoJSON converters and fix error handling for Tileset conversion in OfflineDownload.

2 files changed, 40 insertions, 19 deletions

diff --git a/src/mbgl/style/conversion/geojson.cpp b/src/mbgl/style/conversion/geojson.cpp
index 0fba6e5b4d..8103e9014a 100644
--- a/src/mbgl/style/conversion/geojson.cpp
+++ b/src/mbgl/style/conversion/geojson.cpp
@@ -1,33 +1,26 @@
 #include <mbgl/style/conversion/geojson.hpp>
-
+#include <mbgl/style/conversion/json.hpp>
 #include <mbgl/util/rapidjson.hpp>
 
-#include <string>
-#include <sstream>
+#include <mapbox/geojson.hpp>
+#include <mapbox/geojson/rapidjson.hpp>
 
 namespace mbgl {
 namespace style {
 namespace conversion {
 
-template <>
-optional<GeoJSON> convertGeoJSON(const std::string& string, Error& error) {
-    rapidjson::GenericDocument<rapidjson::UTF8<>, rapidjson::CrtAllocator> d;
-    d.Parse(string.c_str());
-
-    if (d.HasParseError()) {
-        std::stringstream message;
-        message << d.GetErrorOffset() << " - " << rapidjson::GetParseError_En(d.GetParseError());
-        error = { message.str() };
-        return {};
-    }
+optional<GeoJSON> Converter<GeoJSON>::operator()(const std::string& value, Error& error) const {
+    return convertJSON<GeoJSON>(value, error);
+}
 
-    optional<GeoJSON> geoJSON = conversion::convertGeoJSON<JSValue>(d, error);
-    if (!geoJSON) {
-        error = { error.message };
+template <>
+optional<GeoJSON> Converter<GeoJSON>::operator()(const JSValue& value, Error& error) const {
+    try {
+        return mapbox::geojson::convert(value);
+    } catch (const std::exception& ex) {
+        error = { ex.what() };
         return {};
     }
-
-    return geoJSON;
 }
 
 } // namespace conversion
diff --git a/src/mbgl/style/conversion/json.hpp b/src/mbgl/style/conversion/json.hpp
new file mode 100644
index 0000000000..0817ac09df
--- /dev/null
+++ b/src/mbgl/style/conversion/json.hpp
@@ -0,0 +1,28 @@
+#include <mbgl/style/conversion.hpp>
+#include <mbgl/style/rapidjson_conversion.hpp>
+
+#include <string>
+#include <sstream>
+
+namespace mbgl {
+namespace style {
+namespace conversion {
+
+template <class T, class...Args>
+optional<T> convertJSON(const std::string& json, Error& error, Args&&...args) {
+    JSDocument document;
+    document.Parse<0>(json.c_str());
+
+    if (document.HasParseError()) {
+        std::stringstream message;
+        message << document.GetErrorOffset() << " - " << rapidjson::GetParseError_En(document.GetParseError());
+        error = { message.str() };
+        return {};
+    }
+
+    return convert<T, JSValue>(document, error, std::forward<Args>(args)...);
+}
+
+} // namespace conversion
+} // namespace style
+} // namespace mbgl