data-container: Only return names of multi-id topics once, add getter…

… for subscription message-id map

ulog_cpp/data_container.hpp

@@ -6,6 +6,7 @@
 
 #include <memory>
 #include <unordered_map>
+#include <unordered_set>
 #include <vector>
 
 #include "data_handler_interface.hpp"
@@ -87,13 +88,18 @@ class DataContainer : public DataHandlerInterface {
     return _subscriptions_by_name_and_multi_id;
   }
 
+  const std::map<uint16_t, std::shared_ptr<Subscription>>& subscriptionsByMessageId()
+  {
+    return _subscriptions_by_message_id;
+  }
+
   std::vector<std::string> subscriptionNames() const
   {
-    std::vector<std::string> names;
+    std::unordered_set<std::string> names;
     for (const auto& kv : _subscriptions_by_name_and_multi_id) {
-      names.push_back(kv.first.name);
+      names.insert(kv.first.name);
     }
-    return names;
+    return std::vector<std::string>(names.begin(), names.end());
   }
 
   std::shared_ptr<Subscription> subscription(const std::string& name, int multi_id) const