move from_json_object() and to_json_object() into separate header file.

server/pep-utils-json.hh

@@ -0,0 +1,39 @@
+// some helper functions to deal with JSON data
+
+#ifndef PEP_UTILS_JSON_HH
+#define PEP_UTILS_JSON_HH
+
+#include "json_spirit/json_spirit_utils.h"
+
+namespace pEp {
+namespace utility {
+
+	// fetch a member from the given object, if set. (return a sensible NULL/default value if not)
+	template<class T, js::Value_type VALUE_TYPE>
+	T from_json_object(const js::Object& obj, const std::string& key)
+	{
+		const auto v = find_value(obj, key);
+		if(v.type() == js::null_type) return T{};
+		if(v.type() == VALUE_TYPE) return from_json<T>(v);
+		
+		throw std::runtime_error("JSON object has a member for key \"" + key + "\""
+			" with incompatible type " + js::value_type_to_string( v.type())
+			+ " instead of expected type " + js::value_type_to_string(VALUE_TYPE)
+			);
+	}
+
+
+	template<class T>
+	void to_json_object(js::Object& obj, const std::string& key, const T& value)
+	{
+		if(value!=T{})
+		{
+			obj.emplace_back( key, js::Value( to_json<T>(value) ));
+		}
+	}
+
+
+} // end of namespace pEp::utility
+} // end of namespace pEp
+
+#endif // PEP_UTILS_JSON_HH