introduce defaults for the C++ API (#452)

* minimal c++ API test

Signed-off-by: Karsten Knese <karsten@openrobotics.org>

* introduce defaults

Signed-off-by: Karsten Knese <karsten@openrobotics.org>

* open overload for simple uri string

Signed-off-by: Karsten Knese <karsten@openrobotics.org>

* set sqlite3 as a constant

Signed-off-by: Karsten Knese <karsten@openrobotics.org>

rosbag2_cpp/include/rosbag2_cpp/reader.hpp

@@ -21,6 +21,7 @@
 #include <vector>
 
 #include "rosbag2_cpp/converter_options.hpp"
+#include "rosbag2_cpp/readers/sequential_reader.hpp"
 #include "rosbag2_cpp/storage_options.hpp"
 #include "rosbag2_cpp/visibility_control.hpp"
 
@@ -50,10 +51,28 @@ class BaseReaderInterface;
 class ROSBAG2_CPP_PUBLIC Reader final
 {
 public:
-  explicit Reader(std::unique_ptr<reader_interfaces::BaseReaderInterface> reader_impl);
+  explicit Reader(
+    std::unique_ptr<reader_interfaces::BaseReaderInterface> reader_impl =
+    std::make_unique<readers::SequentialReader>());
 
   ~Reader();
 
+  /**
+   * Opens an existing bagfile and prepare it for reading messages.
+   * The bagfile must exist.
+   * This must be called before any other function is used.
+   *
+   * \note This will open URI with the default storage options
+   * * using sqlite3 storage backend
+   * * using no converter options, storing messages with the incoming serialization format
+   * \sa rmw_get_serialization_format.
+   * For specifications, please see \sa open, which let's you specify
+   * more storage and converter options.
+   *
+   * \param storage_uri URI of the storage to open.
+   **/
+  void open(const std::string & uri);
+
   /**
    * Throws if file could not be opened.
    * This must be called before any other function is used.
@@ -67,7 +86,9 @@ class ROSBAG2_CPP_PUBLIC Reader final
    * \param storage_options Options to configure the storage
    * \param converter_options Options for specifying the output data format
    */
-  void open(const StorageOptions & storage_options, const ConverterOptions & converter_options);
+  void open(
+    const StorageOptions & storage_options,
+    const ConverterOptions & converter_options = ConverterOptions());
 
   /**
    * Ask whether the underlying bagfile contains at least one more message.

rosbag2_cpp/include/rosbag2_cpp/writer.hpp

@@ -24,6 +24,7 @@
 #include "rosbag2_cpp/converter_options.hpp"
 #include "rosbag2_cpp/storage_options.hpp"
 #include "rosbag2_cpp/visibility_control.hpp"
+#include "rosbag2_cpp/writers/sequential_writer.hpp"
 
 #include "rosbag2_storage/serialized_bag_message.hpp"
 #include "rosbag2_storage/topic_metadata.hpp"
@@ -50,18 +51,37 @@ class BaseWriterInterface;
 class ROSBAG2_CPP_PUBLIC Writer final
 {
 public:
-  explicit Writer(std::unique_ptr<rosbag2_cpp::writer_interfaces::BaseWriterInterface> writer_impl);
+  explicit Writer(
+    std::unique_ptr<rosbag2_cpp::writer_interfaces::BaseWriterInterface> writer_impl =
+    std::make_unique<writers::SequentialWriter>());
 
   ~Writer();
 
+  /**
+   * Opens a new bagfile and prepare it for writing messages. The bagfile must not exist.
+   * This must be called before any other function is used.
+   *
+   * \note This will open URI with the default storage options
+   * * using sqlite3 storage backend
+   * * using no converter options, storing messages with the incoming serialization format
+   * \sa rmw_get_serialization_format.
+   * For specifications, please see \sa open, which let's you specify
+   * more storage and converter options.
+   *
+   * \param storage_uri URI of the storage to open.
+   **/
+  void open(const std::string & uri);
+
   /**
    * Opens a new bagfile and prepare it for writing messages. The bagfile must not exist.
    * This must be called before any other function is used.
    *
    * \param storage_options Options to configure the storage
    * \param converter_options options to define in which format incoming messages are stored
    **/
-  void open(const StorageOptions & storage_options, const ConverterOptions & converter_options);
+  void open(
+    const StorageOptions & storage_options,
+    const ConverterOptions & converter_options = ConverterOptions());
 
   /**
    * Create a new topic in the underlying storage. Needs to be called for every topic used within

rosbag2_cpp/package.xml

@@ -21,6 +21,8 @@
   <depend>rosidl_typesupport_introspection_cpp</depend>
   <depend>shared_queues_vendor</depend>
 
+  <exec_depend>rosbag2_storage_default_plugins</exec_depend>
+
   <test_depend>ament_cmake_gmock</test_depend>
   <test_depend>ament_lint_auto</test_depend>
   <test_depend>ament_lint_common</test_depend>

rosbag2_cpp/src/rosbag2_cpp/reader.cpp

@@ -16,6 +16,7 @@
 #include "rosbag2_cpp/reader.hpp"
 
 #include <memory>
+#include <string>
 #include <utility>
 #include <vector>
 
@@ -34,6 +35,18 @@ Reader::~Reader()
   reader_impl_->reset();
 }
 
+void Reader::open(const std::string & uri)
+{
+  rosbag2_cpp::StorageOptions storage_options;
+  storage_options.uri = uri;
+  storage_options.storage_id = "sqlite3";
+  storage_options.max_bagfile_size = 0;  // default
+  storage_options.max_cache_size = 0;  // default
+
+  rosbag2_cpp::ConverterOptions converter_options{};
+  return open(storage_options, converter_options);
+}
+
 void Reader::open(
   const StorageOptions & storage_options,
   const ConverterOptions & converter_options)

rosbag2_cpp/src/rosbag2_cpp/readers/sequential_reader.cpp

@@ -227,6 +227,8 @@ void SequentialReader::check_converter_serialization_format(
   const std::string & converter_serialization_format,
   const std::string & storage_serialization_format)
 {
+  if (converter_serialization_format.empty()) {return;}
+
   if (converter_serialization_format != storage_serialization_format) {
     converter_ = std::make_unique<Converter>(
       storage_serialization_format,

rosbag2_cpp/src/rosbag2_cpp/writer.cpp

@@ -31,6 +31,8 @@
 namespace rosbag2_cpp
 {
 
+static constexpr char const * kDefaultStorageID = "sqlite3";
+
 Writer::Writer(std::unique_ptr<rosbag2_cpp::writer_interfaces::BaseWriterInterface> writer_impl)
 : writer_impl_(std::move(writer_impl))
 {}
@@ -40,6 +42,16 @@ Writer::~Writer()
   writer_impl_.reset();
 }
 
+void Writer::open(const std::string & uri)
+{
+  rosbag2_cpp::StorageOptions storage_options;
+  storage_options.uri = uri;
+  storage_options.storage_id = kDefaultStorageID;
+
+  rosbag2_cpp::ConverterOptions converter_options{};
+  return open(storage_options, converter_options);
+}
+
 void Writer::open(
   const StorageOptions & storage_options, const ConverterOptions & converter_options)
 {

rosbag2_tests/test/rosbag2_tests/test_rosbag2_cpp_api.cpp

@@ -44,18 +44,9 @@ TEST(TestRosbag2CPPAPI, minimal_writer_example)
   // in case the bag was previously not cleaned up
   rcpputils::fs::remove_all(rosbag_directory);
 
-  rosbag2_cpp::StorageOptions storage_options;
-  storage_options.uri = rosbag_directory.string();
-  storage_options.storage_id = "sqlite3";
-  storage_options.max_bagfile_size = 0;  // default
-  storage_options.max_cache_size = 0;  // default
-  rosbag2_cpp::ConverterOptions converter_options;
-  converter_options.input_serialization_format = "cdr";
-  converter_options.output_serialization_format = "cdr";
-
   {
-    rosbag2_cpp::Writer writer(std::make_unique<rosbag2_cpp::writers::SequentialWriter>());
-    writer.open(storage_options, converter_options);
+    rosbag2_cpp::Writer writer;
+    writer.open(rosbag_directory.string());
 
     auto bag_message = std::make_shared<rosbag2_storage::SerializedBagMessage>();
     auto ret = rcutils_system_time_now(&bag_message->time_stamp);
@@ -78,8 +69,8 @@ TEST(TestRosbag2CPPAPI, minimal_writer_example)
   }
 
   {
-    rosbag2_cpp::Reader reader(std::make_unique<rosbag2_cpp::readers::SequentialReader>());
-    reader.open(storage_options, converter_options);
+    rosbag2_cpp::Reader reader;
+    reader.open(rosbag_directory.string());
     while (reader.has_next()) {
       auto bag_message = reader.read_next();