Add topics with zero message counts to the SQLiteStorage::get_metadata().

rosbag2_cpp/CMakeLists.txt

@@ -137,6 +137,7 @@ if(BUILD_TESTING)
   find_package(ament_cmake_gmock REQUIRED)
   find_package(ament_lint_auto REQUIRED)
   find_package(test_msgs REQUIRED)
+  find_package(std_msgs REQUIRED)
   find_package(rosbag2_test_msgdefs REQUIRED)
   ament_lint_auto_find_test_dependencies()
 
@@ -188,6 +189,7 @@ if(BUILD_TESTING)
       rosbag2_storage::rosbag2_storage
       rosbag2_test_common::rosbag2_test_common
       ${test_msgs_TARGETS}
+      ${std_msgs_TARGETS}
     )
   endif()
 

rosbag2_cpp/package.xml

@@ -31,6 +31,7 @@
   <test_depend>ament_lint_auto</test_depend>
   <test_depend>ament_lint_common</test_depend>
   <test_depend>test_msgs</test_depend>
+  <test_depend>std_msgs</test_depend>
   <test_depend>rosbag2_test_common</test_depend>
   <test_depend>rosbag2_test_msgdefs</test_depend>
 

rosbag2_cpp/test/rosbag2_cpp/test_sequential_reader.cpp

@@ -32,6 +32,7 @@
 #include "rosbag2_test_common/tested_storage_ids.hpp"
 #include "rosbag2_test_common/temporary_directory_fixture.hpp"
 
+#include "std_msgs/msg/string.hpp"
 #include "test_msgs/msg/basic_types.hpp"
 
 #include "fake_data.hpp"
@@ -249,6 +250,38 @@ TEST_P(ParametrizedTemporaryDirectoryFixture, reader_accepts_bare_file) {
   EXPECT_THAT(reader.get_metadata().topics_with_message_count, SizeIs(1));
 }
 
+TEST_P(ParametrizedTemporaryDirectoryFixture, get_metadata_include_topics_with_zero_messages) {
+  const auto bag_path = rcpputils::fs::path(temporary_dir_path_) / "bag_with_no_msgs";
+  const std::string topic_name = "topic_with_0_messages";
+  const auto storage_id = GetParam();
+  {
+    rosbag2_storage::TopicMetadata topic_metadata;
+    topic_metadata.name = topic_name;
+    topic_metadata.type = "std_msgs/msg/String";
+
+    rosbag2_cpp::Writer writer;
+    rosbag2_storage::StorageOptions options;
+    options.uri = bag_path.string();
+    options.storage_id = storage_id;
+    writer.open(options);
+    writer.create_topic(topic_metadata);
+  }
+
+  rosbag2_storage::MetadataIo metadata_io;
+  ASSERT_TRUE(metadata_io.metadata_file_exists(bag_path.string()));
+  auto metadata_from_yaml = metadata_io.read_metadata(bag_path.string());
+  auto first_storage = bag_path / metadata_from_yaml.relative_file_paths[0];
+
+  rosbag2_storage::StorageFactory factory;
+  rosbag2_storage::StorageOptions options;
+  options.uri = first_storage.string();
+  options.storage_id = storage_id;
+  auto reader = factory.open_read_only(options);
+  auto metadata = reader->get_metadata();
+  ASSERT_THAT(metadata.topics_with_message_count, SizeIs(1));
+  EXPECT_EQ(metadata.topics_with_message_count[0].message_count, 0U);
+}
+
 INSTANTIATE_TEST_SUITE_P(
   BareFileTests,
   ParametrizedTemporaryDirectoryFixture,

rosbag2_storage_sqlite3/src/rosbag2_storage_sqlite3/sqlite_storage.cpp

@@ -770,14 +770,27 @@ void SqliteStorage::add_topic_to_metadata(
     // Before db_schema_version_ = 3 we didn't store metadata in the database and real
     // metadata_.version will be lower than 9
     offered_qos_profiles_str, (db_schema_version_ >= 3) ? metadata_.version : 8);
-  metadata_.topics_with_message_count.push_back(
-    {
-      {
-        get_or_generate_extern_topic_id(inner_topic_id), topic_name, topic_type, ser_format,
-        offered_qos_profiles, type_hash
-      },
-      static_cast<size_t>(msg_count)
+  const rosbag2_storage::TopicMetadata topic_metadata {
+    get_or_generate_extern_topic_id(inner_topic_id), topic_name, topic_type, ser_format,
+    offered_qos_profiles, type_hash};
+  auto & topics_list = metadata_.topics_with_message_count;
+  auto it = std::find_if(
+    topics_list.begin(), topics_list.end(),
+    [&](const rosbag2_storage::TopicInformation & topic_info) {
+      return topic_info.topic_metadata == topic_metadata;
     });
+  if (it != topics_list.end()) {
+    it->message_count = msg_count;
+  } else {
+    metadata_.topics_with_message_count.push_back(
+      {
+        {
+          get_or_generate_extern_topic_id(inner_topic_id), topic_name, topic_type, ser_format,
+          offered_qos_profiles, type_hash
+        },
+        static_cast<size_t>(msg_count)
+      });
+  }
 
   metadata_.message_count += msg_count;
 }
@@ -812,6 +825,15 @@ void SqliteStorage::read_metadata()
   rcutils_time_point_value_t min_time = INT64_MAX;
   rcutils_time_point_value_t max_time = 0;
 
+  // fill in all topics and types even those do not have any messages
+  if (all_topics_and_types_.empty()) {
+    fill_topics_and_types();
+  }
+  metadata_.topics_with_message_count.reserve(all_topics_and_types_.size());
+  for (const auto & topic_metadata : all_topics_and_types_) {
+    metadata_.topics_with_message_count.push_back({topic_metadata, 0});
+  }
+
   if (database_->field_exists("topics", "offered_qos_profiles")) {
     if (database_->field_exists("topics", "type_description_hash")) {
       std::string query =