(This does not imply that the message is a POD - depending on the used field types it can not be mem-copied.). Message type for a ROS 2 topic, specified as a character vector. To define serialization for a type you must define a specialization of the ros::serialization::Serializer class: Alternatively, you can define an "all-in-one" serializer: Note that if you're using an all-in-one serializer, you are not allowed to use anything but stream.next(). changing the way the data is stored internally). Message descriptions are stored in .msg files in the msg/ subdirectory of a ROS . The ROS Wiki is for ROS 1. There was a problem preparing your codespace, please try again. Especially when a ROS graph spans multiple devices and networks the needs within one network are likely already different. So in order to design the message API in a future-proof manner it should not expose the serialization library used but make the actually used serialization library an implementation detail. Join our Slack channel to ask questions, share feedback, and stay up to date on what our team is working on. This feature would also imply backwards-incompatible changes to the ROS IDL. In previous work, we presented ros2_tracing, a framework with instrumentation and. The ROS distribution contains message serializers implemented in C++, Python and Lisp. For each set of max size constraints the message class would require a mangled name: e.g. ROS uses a simplified messages description language for describing the data values (aka messages) that ROS nodes publish.This description makes it easy for ROS tools to automatically generate source code for the message type in several target languages.Message descriptions are stored in .msg files in the msg/ subdirectory of a ROS package. The primitive and primitive array types should generally not be relied upon for long-term use. Other existing serialization libraries provide more features and are tailored for specific needs ranging from small memory footprint over small wire protocol to low performance impact. ROS messages are the primary container for exchanging data in ROS 2. msg ROS 2 message for a given topic object handle. This is an exploration of possible message interfaces and the relation of the underlying message serialization. to use Codespaces. Therefore it would be good if no serialization library needs to be linked if the functionality is not used at all (e.g. The ROS Wiki is for ROS 1. The message used by the userland code stores its data directly. Work fast with our official CLI. Check out the ROS 2 Documentation. Say you want to adapt your own vector struct for use with roscpp that is compatible with geometry_msgs/Vector3: To instead use the 3-function serializer: In case you need further control on the generated message headers, or want to provide additional custom methods which can be used with your messages, it is possible to do so via adding specific macros, or providing a full header for your message type. // Ensure that if the definition of geometry_msgs/Vector3 changes we have a compile error here. The ROS 2 executor, a high-level task scheduler which handles messages internally, is a performance bottleneck. As described above, the following topics and message types being published to Nav2 in this scenario are: 5.3.1. ROS 1 messages are data objects which use member-based access to the message fields. Method 1: The ROS distribution. However, in order to support dictionaries in as many languages as we can, we have to take into consideration whether all languages provide mechanisms for supporting them. compactness of wire format). In ROS1 it is possible to leverage your own data structure within a message shown in the wiki below. The default middleware for ROS 2 is DDS which has cdr as its default binary serialization format. I am interested to learn if there is an equivalent process for ROS2? Anything requiring more complicated behavior should use the 3-function split version. The features of a serialization library can be extrinsic (exposed functionality through API, e.g. This article captures the research done in regards to the serialization component, including an overview of the current implementation in ROS 1 and the alternatives for ROS 2. Please see roscpp: Messages serialization and adapting types. 20 comments anacsousa1 commented on Jul 27, 2020 Cloning the branch https://github.com/mabelzhang/rosbag2/tree/rosbag2_py: git clone https://github.com/mabelzhang/rosbag2/tree/rosbag2_py. E.g. This is an exploration of possible message interfaces and the relation of the underlying message serialization. Please start posting anonymously - your entry will be published after you log in or create a new account. Change the name of the ROS2 bag when recording Install the ROS2 distribution. It is also likely that in the near future more libraries with new advantages (and disadvantages) will come up. The name of these macros follow the structure _MESSAGE__PLUGIN_, where is one of CONSTRUCTOR, CLASS_BODY, SERIALIZER, PRINTER. ROS could build on top of one specific implementation of DDS. Wiki: roscpp/Overview/MessagesSerializationAndAdaptingTypes (last edited 2019-09-06 20:32:38 by MarcinPanek), Except where otherwise noted, the ROS wiki is licensed under the, // compile-time assert that sizeof(MyVector3) == serializationLength(x) + serializationLength(y) + serializationLength(z). Protobuf) are definitely not binary compatible when features like optional fields are being used (check this assumption). But for example a byte array is represented differently in C++ in the various serialization libraries: Furthermore the serialization library specific message API might not expose mutable access which could therefore not be provided by RO either when using pipeline C. Due to the mentioned problems and added complexity the pipeline C is not viable. Since the data is stored directly in the serialization library specific representation copying the data before serializing it is not necessary anymore. This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository. You will also need to add an install target for these headers in your package CMakeLists.txt, e.g. The message values need are sent in YAML format. It is expected that there are one or more message serialization implementations which can be used, such as Protobuf, MessagePack and Thrift. A tag already exists with the provided branch name. Since we do not have the need to make the storage backend exchangeable anymore and we might prefer keeping the member based access of messages to keep it similar with ROS 1. I am interested to learn if there is an equivalent process for ROS2? roscpp_serialization contains the code for serialization as described in MessagesSerializationAndAdaptingTypes . This document pre-dates the decision to build ROS 2 on top of DDS. Notice that you have to provide a default value (or an additional default constructor), as ROS messages are required to be default constructible because in the subscription pipeline a new instance is constructed and then passed to the deserializer (customization would be possible via traits). When developing the serialization of the PointCloud2 type we took an opinionated approach. While the message specification is not very feature rich the serializer is pretty fast. This still allows us to implement the optimization described as pipeline B for e.g. Python), thanks to being built-in data types. The rules/conventions for message files: Use CamelCase for the name of the interface. It fails add a comment 1 Answer std_msgs provides many basic message types. to include custom field or use custom data types, you can as well provide the full header of your message: instead of placing it in my_pkg/include/my_pkg/plugin/MyVector3.h, place it in my_pkg/include/my_pkg/MyVector3.h. How can I set the footprint of my robot in nav2? Version: 1.0.7 was published by foxglovebot. This paper is focused on specifying the message API and designing the integration with the serialization with performance as well as flexibility in mind. Towards Zero-Copy (TZC) aims to reduce the times of data copy and serialization in the ROS2. Open the main ActionGraph by expanding Carter_ROS. New in gencpp 0.6.2 If you create file my_pkg/include/my_pkg/plugin/MyVector3.after.h, it will be included at the end of the generated message header. IoT resources probably are better than robotics and other resources for looking for a more DDS-like system with some of the messaging and config features. Are you sure you want to create this branch? This is an exploration of possible DDS in ROS2 No reinvent the wheel! Nodes can also exchange a request and response message as part of a ROS service call. In the case of pipeline A where only the ROS message is part of the nodelet library (the serialization specific code is only part of the nodelet manager) both revisions must be binary compatible. ROS2 gazebo_ros2_control . - Provide power users a choice point. Under the assumption that we want to avoid implementing the serialization process from a custom message class into each supported serialization format (pipeline B) the process will either require one extra copy of the data (pipeline A) or the message must directly store its data in the specific message representation of the used serialization library (pipeline C). Download and share free MATLAB code, including functions, models, apps, support packages and toolboxes This command takes three arguments: service_name: The name of the service. it is possible to customize the generated header by defining the appropriate macros in the file my_pkg/include/my_pkg/plugin/MyVector3.h. When you press CTRL+C the bag will stop all subscribers and no more message will be added to the bag. - DDS is end-to-end vs build from multiple software -> dependencies - Documented, formal specification and API. The messages are a crucial part of ROS since they are the interface between functional components and are exposed in every userland code. Since this use case implies severe constraints that are not optimal for scenarios where dynamic memory allocation is feasible this should not limit the solution but should be provided as an alternative implementation. On the other hand a method-based interface allows to implement arbitrary storage paradigms behind the API. The serialization library will perform the serialization into the wire format from there. roscpp_serialization contains the code for serialization as described in Message serialization are important functions for these robotics middleware. values: The actual message sent to the service. Conceptually only the intrinsic features can be exploited when a serialization library is used internally, e.g. The documentation for this class was generated from the following file: include/rclcpp/ serialization.hpp Learn more. Choosing pipeline A over pipeline B or C should therefore not impose any significant performance hit. GitHub - foxglove/rosmsg2-serialization: ROS 2 (Robot Operating System) message serialization, for reading and writing bags and network messages main 1 branch 10 tags Go to file Code jhurliman v1.0.7 1e051fb on Sep 12 27 commits .github/ workflows Run CI on PR events 15 months ago .vscode 0.0.0 (MessageReader only) 16 months ago src ROS2 Message Serialization Adapting Types ros2 custom-message asked Jul 6 '20 Levi-Armstrong 106 2 5 6 In ROS1 it is possible to leverage your own data structure within a message shown in the wiki below. Only a few messages are intended for incorporation into higher-level messages. ROS2 defaulted FastRTPS. Supported by the Apache Software Foundation. When message objects are used in nodelets one problem is that two nodelets which run in the same process might have been linked against different definitions of a message. You signed in with another tab or window. The selection of one serialization library has a much higher impact on the performance. This assumes that the API of the serialization library specific representation can be wrapped inside the ROS message API (see Technical Issues -> Variances in field types). But those can only be mapped to the specific API of the serialization library if the types are exchangeable. Please Remember that it is then up to you to specify the full expected API compatible to the provided message definition, including message_traits, serialization, and message_operations. DDS API in OMG specification -> ROS2 is DDS vendor independent. A future change of this API would require a significant amount of work. . This article specifies the file format describing the data structures exchanged by ROS 2 components to interact with each other. Check out the ROS 2 Documentation, roscpp overview: Initialization and Shutdown | Basics | Advanced: Traits [ROS C Turtle] | Advanced: Custom Allocators [ROS C Turtle] | Advanced: Serialization and Adapting Types [ROS C Turtle] | Publishers and Subscribers | Services | Parameter Server | Timers (Periodic Callbacks) | NodeHandles | Callbacks and Spinning | Logging | Names and Node Information | Time | Exceptions | Compilation Options | Advanced: Internals | tf/Overview | tf/Tutorials | C++ Style Guide. If nothing happens, download GitHub Desktop and try again. Generated code is not header only; requires compilation and linking. Let's see how to define custom methods for MyVector3. The solution seems to be to replace the last line with: Due to the template-based serialization system used by roscpp since ROS 1.1, it is possible to adapt an external type for use with ROS publish/subscribe without modifying that type at all. For more information on sending and receiving messages, see Exchange Data with ROS 2 Publishers and Subscribers.. To identify its data structure, each message has a message type.For example, sensor data from a laser . USE ROS2 MOVING FORWARD. Create your own ROS2 custom message (Msg) Create the message file In your newly created package, go inside the msg/ folder and create a new file there. Authors: William Woodall All messages published on this topic will be recorded. 12 comments nyxaria commented on Aug 23, 2020 edited https://github.com/ros2/rosbag2/blob/master/rosbag2_transport/src/rosbag2_transport/generic_publisher.hpp This document pre-dates the decision to build ROS 2 on top of DDS. The message fields can be serialized directly into the wire format using custom code. Authors: Dirk Thomas Date Written: 2015-06 See https://github.com/ros2/prototypes/tree/master/c_fixed_msg for benchmark results of serialization libraries. Each serialization library has certain pros and cons depending on the scenario. operators on the message types. Ros 1 is end of life in 1 year and there is little reason not to upgrade now. @foxglove/rosmsg2-serialization is licensed under MIT License. This block diagram shows the ROS2 messages required for Nav2. . Both pipeline A as well as C a possible to implement using a small layer around an external serialization libraries to adapt them to the message API and make them pluggable into the ROS message system. Messages (.msg) ColorRGBA: A single RGBA value for . The needs might even be different within one ROS graph but different entities. Commonly the methods can be inlined in languages like C++ so they dont pose a significant performance hit but depending on the utilized storage the API might not expose mutable access to the fields which can imply an overhead when modifying data in-place. This paper is focused on specifying the message API and designing the integration with the serialization with performance as well as flexibility in mind. This package is a component of roscpp. ros2/rmw_connext Skip to content Sign up Product Features Mobile Actions Codespaces Packages Security Code review Issues Integrations GitHub Sponsors Customer stories Team Enterprise Explore collapse all. on a self-contained product without external connections). Technical Issues -> Variances in field types, https://github.com/ros2/prototypes/tree/master/c_fixed_msg, dynamic array: RepeatedField (STL-like interface). are supported, as are arrays of primitive types. define `MY_PKG_MESSAGE_MYVECTOR3_PLUGIN_CONSTRUCTOR` \, MyVector3_(double x = 0, double y = 0, double z = 0) \, define `MY_PKG_MESSAGE_MYVECTOR3_PLUGIN_CLASS_BODY` \, return std::sqrt(x * x + y * y + z * z); \, Advanced: Custom Allocators [ROS C Turtle], Customizing generated message headers for C++, Example: define global namespace operators. If you want to add multiple methods, they all need to be defined in the same macro instance. roscpp_serialization contains the code for serialization as described in Do you need discovery, data transport, and message serialization all in one thing? By design, ROS 2 is middleware agnostic and thus can leverage multiple communication frameworks. ROS2 (Robot Operating System) message serialization, for reading and writing bags and network messages. Therefore a method-based interface is preferred as it allows future customizations (e.g. As the results of produce_consume_struct and produce_consume_method show the performance difference is not measurable. Are you using ROS 2 (Dashing/Foxy/Rolling)? This can be the case for any of the pipelines. The major advantage of this approach is that ROS 2 can leverage an existing and well developed implementation of that standard. Maintainer status: maintained Maintainer: Dirk Thomas <dthomas AT osrfoundation DOT org> Author: Josh Faust License: BSD Source: git https://github.com/ros/roscpp_core.git (branch: noetic-devel) 2. The message delegates the data storage to an internally held storage backend, e.g. in real time systems. ROS 2 message for a given topic, returned as an object handle. For ROS 2 the decision has been made to build it on top of an existing middleware solution (namely DDS ). In order to reduce the future maintenance effort existing libraries should be used in order not to specify and implement yet another wire protocol. ROS2 (Robot Operating System) message serialization, for reading and writing bags and network messages rosros2robotoperatingsystemcdrserializationdeserializationserderosbag 1.0.6 Published 5 months ago @foxglove/rostime ROS (Robot Operating System) Time and Duration primitives and helper methods rostimerosros2robotoperatingsystemtimedateduration Publishers and subscribers exchange data using messages on specified topics to carry data between nodes. Optional variant of a message which avoids dynamic memory allocation e.g. your IDE behaves better with it). ROS Index BETA. If multiple communication channels use different serialization formats the publisher should still choose one of them as the storage format for the created message instance to avoid at least one of the necessary storage conversions. The methods could either just access some private member variable directly or delegate the data storage to a separate entity which could e.g. At the same time we could also provide sane values for certain APIs, such as for sensors. It allows the integration of zenoh applications with ROS2, or the tunneling of ROS2 communications between nodes via the zenoh protocol at Internet scale. Extended Capabilities. Use Git or checkout with SVN using the web URL. Ex: "MotorTemperature". Besides that the community provided implementations for other languages, like C, Ruby, MatLab, etc. ROS 2 (Robot Operating System) message serialization, for reading and writing bags and network messages. behind a method-based message interface. However, the performance of ROS2 has become the bottleneck of these real-time systems. Install realsense2_camera from The RealSense distribution: This option is demonstrated in the .travis.yml file. Are you using ROS 2 (Dashing/Foxy/Rolling)? Furthermore member-based access makes it problematic to add support for optional field. optional fields) or intrinsic (e.g. add value range validation, defer storage, implement thread safety, custom logging for debugging/introspection purposes) and enable to drop in custom storage backends (e.g. Serializing messages (small as well as big ones) is at least two orders of magnitude slower than accessing message fields and copying messages in memory. So a very important goal is to make the message interface flexible enough to be future-proof. Start using Socket to analyze @foxglove/rosmsg2-serialization and its 3 dependencies to secure your app from supply chain attacks. From our observations, we find that it can take a large amount of time to serialize complex message in. DDS match ROS requirements A convenient effect of this approach is that extensions applied to a message type will immediately apply to that message nested instances as well. ROS 2 Message Research. if we add optional fields to the message IDL one might contain the version without the optional field while the other does contain the extended version of the message. The previous conclusion to switch from member to method based access has been revisited. Bridge between ROS2/DDS and Eclipse zenoh (https://zenoh.io). If you need even more control, e.g. Standard primitive types (integer, floating point, boolean, etc.) Custom-defined components will replace the auto-generated ones. Consider you have a simple message definition. . This is done through a set of specialized traits classes, as well as a specialized Serializer class. roscpp messages can be serialized to memory easily using the ros::serialization::serialize () function. When considering existing libraries for serialization this approach implies a performance overhead since the message must either be copied into the object provided by the serialization library (implying an additional copy) or custom code must be developed which serializes the message fields directly into the wire format (while bypassing the message class of the serialization library). Since the amount of time necessary for the memory copy before a serialization is orders of magnitudes smaller than the actual serialization pipeline A is selected for further prototyping. 2022. If nothing happens, download Xcode and try again. Constructor & Destructor Documentation Serialization () template<typename MessageT > Constructor of Serialization. 5. Bridge between ROS2/DDS and Eclipse zenoh (https://zenoh.io). Certain semantics will have to be considered in the IDL, such as what datatypes can be used as keys. This article makes the case for using DDS as the middleware for ROS, outlining the pros and cons of this approach, as well as considering the impact to the user experience and code API that using DDS would have. These are example contents of the file that add a comparison operator based on the ordering of x coordinates of the vector: Note that you don't have to include the generated message header in this file (but you can if e.g. . ROS2 (Robot Operating System) message serialization, for reading and writing bags and network messages. the serialization library specific message representation. See https://github.com/ros2/prototypes/tree/master/c_fixed_msg for a prototype illustrating the concept. Different serialization libraries specify different field type when e.g. The two different binary representations will break the ability to exchange them using a shared pointer. The project leverages existing API from the ROS Toolbox in some MATLAB System blocks to process ROS/ROS2 messages over UDP or Serial communication. RTPS has been adopted as the middleware for the ROS2 (Robot Operating System). In the case of pipeline C some serialization libraries (e.g. It's time to use the ros2 service call command to call the service. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Don't add "Msg" or "Interface" in the name, this will add redundancy. In ROS 1, messages and services require all data members and arguments to be specified. Looking further at the output of ros2 bag info, we can see another field attached to each topic called Serialization Format. roscpp_serialization provides the ros::serialization API used in roscpp and should not be used directly. This package is a component of roscpp. Under the assumption that a method-based access is not significantly impacting the performance it is preferred over a member-based access in order to enable changing the storage backend in the future and enabling overriding it with a custom implementation. Authors: Dirk Thomas and Esteve Fernandez. Similar depending on the network connectivity the importance of the size of the wire format varies. Note: If you are building on a memory constrained . Output Arguments. Cons Doesn't support all types that ROS messages currently do (e.g., fixed width 16 byte signed/unsigned ints, only doubles but not floats). It basically summerize the elaborate instructions in the following 2 steps: 2-1. ros2node | ros2publisher | ros2subscriber | ros2. While this avoids the extra data copy it requires a significant effort for implementing the custom serialization routine. For the usage on a small embedded device the constraints regarding the programming language and the available resources is very different from when being used on a desktop computer. Wiki: roscpp_serialization (last edited 2011-07-15 08:16:26 by KenConley), Except where otherwise noted, the ROS wiki is licensed under the, https://code.ros.org/svn/ros/stacks/ros_comm/tags/ros_comm-1.4.8, roscpp: Messages serialization and adapting types, Maintainer: Dirk Thomas . TZC uses an algorithm called partial serialization, cutting a message into two parts. - DDS implementations usually do not introduce dependencies. Therefore performing a message copy (from one data representation to the serialization library data representation) can be considered a neglectable overhead since the serialization is the clear performance bottleneck. Although this can be done from any language, one particularly useful situation is for portable C99, for use in everything from microcontrollers to soft-core processors on FPGAs, to screwed hard real-time environments. any message class of an existing serialization which suits our API). Except where otherwise noted, these design documents are licensed under Creative Commons Attribution 3.0. generating C++ code for the messages. Therefore a templated backend is preferred as it allows customizations (e.g. With the transition to use IDL for specifying interfaces in ROS 2 Dashing this article has been superseded by the Interface definition using .msg / .srv / .action files article. With the goal to dynamically choose between the former node and nodelet style of composing a system the important the amount of scenarios where messages are actually serialized (rather than passed by reference) is likely to decrease. the default serialization library if need is. ros2 bag record will create a SQLite3 database (database inside a file) and put it inside a folder, which name is the name of the bag. From a performance point of view the message interface should expose const references (especially to big fields). This approach would also encourage a clean modular design. This package is a component of roscpp. However, other middleware . The Fast RTPS bridge allows us to better integrate with ROS2, making it easy to share sensor values, commands, and other vehicle information. GitHub Actions will take care of the rest. This document pre-dates the decision to build ROS 2 on top of DDS. For each type a default max size could be provided as well as each field could have a specific custom override in the message IDL. MessagesSerializationAndAdaptingTypes. This project relies on ROS Toolbox functionality to provide basic integration of Simulink targets, with focus on Simulink Real-Time and Speedgoat, into ROS/ROS2 networks via message serialization. This can be used to define free functions (functions in the global namespace), e.g. Generate a special message class which acts as a POD which is mem-copyable as well as without any dynamic memory allocation. Messages can include arbitrarily nested structures and arrays (much like C structs). See Adapting a custom Vector3 for an example redefinition of the other necessary message headers components. These fields are then serialized directly into the wire format. Each publisher can act as a factory for message instances and create messages for the userland code which fit the currently used communication channels and their serialization format best. Due to the broad domains where ROS is being (and will be) used and their different requirements and constraints we could not identify a single serialization library which matches all of them perfectly well. The possible approaches to select the serialization library vary from a compile decision to being able to dynamically select the serialization library for each communication channel. roscpp messages can also be deserialized from memory quite easily. For each communication channel the message data is then copied into the serialization specific message representation. This article captures the research done in regards to the serialization component, including an overview of the current implementation in ROS 1 and the alternatives for ROS 2. service_type: The type message received by of the service. The results of the "ros_dds" prototype are also summarized and used in the exploration of the issue. As they are encoded in the ROS2 message type, PointCloud2 follows the array of structs approach. class rclcpp::Serialization< MessageT > Default implementation to (de)serialize a message by using rmw_ (de)serialize. The equivalent functionality we're planning to implement is Type Masquerading, but it's still on the Roadmap: https://index.ros.org/doc/ros2/Roadmap/ Our research showed that it was hard to match or beat the default serialization and teh cost of the extra copy initially is much less expensive compared to the serialization so custom serialization makes adapting types more work and more error prone and likely less performant. Therefore a dynamic solution is preferred. For more information about ROS 2 interfaces, see index.ros2.org. Alternatively, additional custom constructors can also be added without replacing the default one by defining them as custom methods. http://wiki.ros.org/roscpp/Overview/M. A message is a simple data structure, comprising typed fields. By definition each message object stores its data directly in its members which implies the lowest overhead at runtime. Fast serialization/deserialization for dynamic languages thanks to native extensions. For example: Toggle line numbers TODO add more benefits from whiteboard picture Serializatoin Pluggability. For the later approach the decision can be made transparent to the userland code. With the decision to build ROS 2 on top of DDS the Pipeline B will be used. In our approach, we employ the struct of arrays type of . The traits required for publish/subscribe are detailed at the message traits page. IMPORTANT: be careful, as doing so might break the expected message API and/or compatibility with other languages. The major problem is the mapping between those types in an efficient manner. A message interface which utilizes member-based access to the message fields is a straightforward API. This description makes it easy for ROS tools to automatically generate source code for the message type in several target languages. It was originally planned for this demo: https://github.com/ros2/ros2/issues/55 and there's some sketches of approach planned at the time. in C99 Foo_10_20 would represent a message Foo where the two dynamic sized fields have max sizes of 10 and 20. MessagesSerializationAndAdaptingTypes. If you want high performance make sure to stay with compatible pointers to avoid interprocess communications and then you won't have to serialize. That is, each point (struct) is packed together and serialized linearly together in memory. By only serializing the necessary information in one part, TZC improves the general . Dictionaries or maps are widely used in several programming languages (e.g. Carter_ROS OmniGraph Nodes Go to Isaac Examples -> ROS -> Navigation to load the warehouse scenario. New in gencpp 0.6.2 To add functions using the generated class to the global namespace, create file my_pkg/include/my_pkg/plugin/MyVector3.after.h. As the results of produce_consume_method and produce_consume_backend_plain show the performance difference is again not measurable. Install ROS2 Dashing, on Ubuntu 18.04 or ROS2 Foxy, on Ubuntu 20.04. This is complementary to Adapting C++ types outlined above, in the sense that you start from a message definition and allow for additional / more fine-grained control of the generated object type, instead of the other way around. By using optional fields and default values, we can define simpler APIs so that users' code can be more succinct and more readable. 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