sjparser: Value<double> should also support yajl integers

Previosly, sjparser was rejecting payloads like

   {
     "lat": 0,
     "lon": 0
   }

when using Value<double> ... However, since API users could
send both 0 and 0.0, we need to extent the allowed yajl types.

contrib/sjparser/library/sjparser/internals/token_parser.cpp

@@ -88,5 +88,9 @@ void TokenParser::on(ArrayEndT /*unused*/) {
   unexpectedToken("array end");
 }  // LCOV_EXCL_LINE
 
+void TokenParser::on(DummyT) {
+  unexpectedToken("dummy");
+}
+
 void TokenParser::childParsed() {}
 }  // namespace SJParser

contrib/sjparser/library/sjparser/internals/token_parser.h

@@ -26,9 +26,11 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #include <stdexcept>
 #include <string>
 #include <string_view>
+#include <vector>
 
 namespace SJParser {
 
+struct DummyT {}; // not used by yajl
 struct NullT {};
 struct MapStartT {};
 struct MapKeyT {
@@ -46,9 +48,28 @@ template <> struct TokenTypeResolver<std::string> {
   using type = std::string_view;
 };
 
+template <> struct TokenTypeResolver<double> {
+  using type = double;
+};
+
 template <typename TokenT>
 using TokenType = typename TokenTypeResolver<std::decay_t<TokenT>>::type;
 
+// TokenSecondaryTypeResolver is used to indicate that a type (e.g. double)
+// should also process yajl events for other data types (e.g. integers)
+// Yajl treats numbers without decimal points as integer, and this
+// triggers an error in case of Value<double>.
+template <typename TokenT> struct TokenSecondaryTypeResolver {
+  using type = DummyT;
+};
+
+template <> struct TokenSecondaryTypeResolver<double> {
+  using type = int64_t;
+};
+
+template <typename TokenT>
+using TokenSecondaryType = typename TokenSecondaryTypeResolver<std::decay_t<TokenT>>::type;
+
 class Dispatcher;
 
 class TokenParser {
@@ -70,6 +91,7 @@ class TokenParser {
   virtual void on(MapEndT /*unused*/);
   virtual void on(ArrayStartT /*unused*/);
   virtual void on(ArrayEndT /*unused*/);
+  virtual void on(DummyT);
 
   virtual void childParsed();
 

contrib/sjparser/library/sjparser/value.cpp

@@ -63,6 +63,14 @@ template <typename ValueT> void Value<ValueT>::on(TokenType<ValueT> value) {
   endParsing();
 }
 
+template <typename ValueT> void Value<ValueT>::on(TokenSecondaryType<ValueT> value) {
+  if constexpr (!std::is_same_v<TokenSecondaryType<ValueT>, SJParser::DummyT>) {
+    setNotEmpty();
+    _value = value;
+    endParsing();
+  }
+}
+
 template <typename ValueT> void Value<ValueT>::finish() {
   if (_on_finish && !_on_finish(_value)) {
     throw std::runtime_error("Callback returned false");

contrib/sjparser/library/sjparser/value.h

@@ -111,6 +111,7 @@ template <typename ValueT> class Value : public TokenParser {
 
  private:
   void on(TokenType<ValueType> value) override;
+  void on(TokenSecondaryType<ValueType> value) override;
   void finish() override;
 
   ValueType _value;