Added a sample support node subscribes string and publishes its CRC32.

README.md

@@ -71,3 +71,15 @@ Please also check for more details about example applications on the embedded de
   - or, `$ ros2 launch mros2_pub_pose launch.py`
 - mros2 application on the embedded device:
   - [sub_pose](https://github.com/mROS-base/mros2-mbed/tree/main/workspace/sub_pose)
+
+## mros2_sub_long_string_pub_crc
+
+- Description:
+  - (The mros2 node on the embedded device publishes `string` (`std_msgs::msg::String`) message to `/to_linux` topic.)
+  - The `sub_long_string_pub_crc` node on the host subscribes `string` (`geometry_msgs::msg::String`) message from `/to_linux` topic, and then its node publishes the CRC32 as a u_int32 (`std_msgs::msg::UInt32`) value to `/to_stm` topic.
+- Host operation:
+  - `$ ros2 run  mros2_sub_long_string_pub_crc sub_long_string_pub_crc_node.
+  - or, `$ ros2 launch mros2_sub_long_string_pub_crc subpub.launch.py`
+- mros2 application on the embedded device:
+  - [sub_pose](https://github.com/mROS-base/mros2-mbed/tree/main/workspace/pub_long_string_sub_crc)
+

mros2_sub_long_string_pub_crc/CMakeLists.txt

@@ -0,0 +1,51 @@
+cmake_minimum_required(VERSION 3.5)
+project(mros2_sub_long_string_pub_crc)
+
+# Default to C99
+if(NOT CMAKE_C_STANDARD)
+  set(CMAKE_C_STANDARD 99)
+endif()
+
+# Default to C++14
+if(NOT CMAKE_CXX_STANDARD)
+  set(CMAKE_CXX_STANDARD 14)
+endif()
+
+if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+  add_compile_options(-Wall -Wextra -Wpedantic)
+endif()
+
+# find dependencies
+find_package(ament_cmake REQUIRED)
+find_package(rclcpp REQUIRED)
+find_package(std_msgs REQUIRED)
+# uncomment the following section in order to fill in
+# further dependencies manually.
+# find_package(<dependency> REQUIRED)
+
+add_executable(sub_long_string_pub_crc_node src/sub_long_string_pub_crc.cpp)
+ament_target_dependencies(sub_long_string_pub_crc_node rclcpp std_msgs)
+
+target_include_directories(sub_long_string_pub_crc_node PUBLIC
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+  $<INSTALL_INTERFACE:include>)
+
+install(TARGETS sub_long_string_pub_crc_node
+  DESTINATION lib/${PROJECT_NAME})
+
+install(DIRECTORY
+  launch
+  DESTINATION share/${PROJECT_NAME})
+
+if(BUILD_TESTING)
+  find_package(ament_lint_auto REQUIRED)
+  # the following line skips the linter which checks for copyrights
+  # uncomment the line when a copyright and license is not present in all source files
+  #set(ament_cmake_copyright_FOUND TRUE)
+  # the following line skips cpplint (only works in a git repo)
+  # uncomment the line when this package is not in a git repo
+  #set(ament_cmake_cpplint_FOUND TRUE)
+  ament_lint_auto_find_test_dependencies()
+endif()
+
+ament_package()

mros2_sub_long_string_pub_crc/launch/subpub.launch.py

@@ -0,0 +1,14 @@
+from launch import LaunchDescription
+from launch_ros.actions import Node
+
+# Note: `node_`, `prefix` and `output` will be removed on Foxy
+def generate_launch_description():
+  return LaunchDescription([
+    Node(
+      package='mros2_sub_long_string_pub_crc',
+      executable='sub_long_string_pub_crc_node',
+      name='subpub_mros2',
+      prefix=['stdbuf -o L'],
+      output="screen"
+    )
+  ])

mros2_sub_long_string_pub_crc/package.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0"?>
+<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<package format="3">
+  <name>mros2_sub_long_string_pub_crc</name>
+  <version>0.0.0</version>
+  <description>TODO: Package description</description>
+  <maintainer email="[email protected]">uden</maintainer>
+  <license>TODO: License declaration</license>
+
+  <buildtool_depend>ament_cmake</buildtool_depend>
+  <build_depend>rclcpp</build_depend>
+  <build_depend>std_msgs</build_depend>
+  <exec_depend>rclcpp</exec_depend>
+  <exec_depend>std_msgs</exec_depend>
+  <test_depend>ament_lint_auto</test_depend>
+  <test_depend>ament_lint_common</test_depend>
+
+  <export>
+    <build_type>ament_cmake</build_type>
+  </export>
+</package>

mros2_sub_long_string_pub_crc/src/sub_long_string_pub_crc.cpp

@@ -0,0 +1,74 @@
+#include <chrono>
+#include <functional>
+#include <memory>
+#include <string>
+
+#include "rclcpp/rclcpp.hpp"
+#include "std_msgs/msg/string.hpp"
+#include "std_msgs/msg/u_int32.hpp"
+
+using std::placeholders::_1;
+
+// imported from
+// https://github.com/aeldidi/crc32/blob/master/src/crc32.c
+uint32_t
+crc32_for_byte(uint32_t byte)
+{
+	const uint32_t polynomial = 0xEDB88320L;
+	uint32_t       result     = byte;
+	size_t         i          = 0;
+
+	for (; i < 8; i++) {
+		result = (result >> 1) ^ (result & 1) * polynomial;
+	}
+	return result;
+}
+
+uint32_t
+crc32(const void *input, size_t size)
+{
+  const uint8_t *current = static_cast<const uint8_t *>(input);
+	uint32_t       result  = 0xFFFFFFFF;
+	size_t         i       = 0;
+
+	for (; i < size; i++) {
+		result ^= current[i];
+		result = crc32_for_byte(result);
+	}
+
+	return ~result;
+}
+
+class Crc32generator : public rclcpp::Node
+{
+public:
+  Crc32generator() : Node("recv_long_string_send_crc_node")
+  {
+    publisher_ = this->create_publisher<std_msgs::msg::UInt32>("to_stm", 10);
+    subscriber_ = this->create_subscription<std_msgs::msg::String>("to_linux", rclcpp::QoS(10).best_effort(), std::bind(&Crc32generator::topic_callback, this, _1));
+  }
+
+private:
+  void topic_callback(const std_msgs::msg::String::SharedPtr msg) const
+  {
+    auto pub_msg = std_msgs::msg::UInt32();
+    uint32_t tmp = crc32((char *)&msg->data[0], msg->data.size());
+    pub_msg.data = tmp;
+    RCLCPP_INFO(this->get_logger(), "\r\nSubscribed msg: '%s'", msg->data.c_str());
+    RCLCPP_INFO(this->get_logger(), "\r\n");
+    RCLCPP_INFO(this->get_logger(), "========================");
+    RCLCPP_INFO(this->get_logger(), "CRC: 0x%0x", tmp);
+    RCLCPP_INFO(this->get_logger(), "========================");
+    publisher_->publish(pub_msg);
+  }
+  rclcpp::Publisher<std_msgs::msg::UInt32>::SharedPtr publisher_;
+  rclcpp::Subscription<std_msgs::msg::String>::SharedPtr subscriber_;
+};
+
+int main(int argc, char * argv[])
+{
+  rclcpp::init(argc, argv);
+  rclcpp::spin(std::make_shared<Crc32generator>());
+  rclcpp::shutdown();
+  return 0;
+}