Calculate type hash from TypeDescription (rep2011)

rcl/CMakeLists.txt

@@ -4,6 +4,7 @@ project(rcl)
 
 find_package(ament_cmake_ros REQUIRED)
 
+find_package(libyaml_vendor REQUIRED)
 find_package(rcl_interfaces REQUIRED)
 find_package(rcl_logging_interface REQUIRED)
 find_package(rcl_yaml_param_parser REQUIRED)
@@ -13,6 +14,8 @@ find_package(rmw_implementation REQUIRED)
 find_package(rosidl_runtime_c REQUIRED)
 find_package(service_msgs REQUIRED)
 find_package(tracetools REQUIRED)
+find_package(type_description_interfaces REQUIRED)
+find_package(yaml REQUIRED)
 
 include(cmake/rcl_set_symbol_visibility_hidden.cmake)
 include(cmake/get_default_rcl_logging_implementation.cmake)
@@ -64,6 +67,7 @@ set(${PROJECT_NAME}_sources
   src/rcl/subscription.c
   src/rcl/time.c
   src/rcl/timer.c
+  src/rcl/type_hash.c
   src/rcl/validate_enclave_name.c
   src/rcl/validate_topic_name.c
   src/rcl/wait.c
@@ -86,6 +90,8 @@ ament_target_dependencies(${PROJECT_NAME}
   "rosidl_runtime_c"
   "service_msgs"
   "tracetools"
+  "type_description_interfaces"
+  "yaml"
 )
 
 # Causes the visibility macros to use dllexport rather than dllimport,
@@ -127,6 +133,7 @@ ament_export_dependencies(${RCL_LOGGING_IMPL})
 ament_export_dependencies(rosidl_runtime_c)
 ament_export_dependencies(service_msgs)
 ament_export_dependencies(tracetools)
+ament_export_dependencies(type_description_interfaces)
 
 if(BUILD_TESTING)
   find_package(ament_lint_auto REQUIRED)

rcl/include/rcl/type_hash.h

@@ -0,0 +1,79 @@
+// Copyright 2023 Open Source Robotics Foundation, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef RCL__TYPE_HASH_H_
+#define RCL__TYPE_HASH_H_
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+#include "rcl/types.h"
+#include "rcl/visibility_control.h"
+#include "rcutils/sha256.h"
+#include "rosidl_runtime_c/type_hash.h"
+#include "type_description_interfaces/msg/type_description.h"
+
+/// Given a TypeDescription, output a string of the hashable JSON representation of that data.
+/**
+ * The output here is generally hashed via rcl_calculate_type_hash() below.
+ * Compare this reference implementation with the .json output files from
+ * `rosidl_generator_type_description.generate_type_hash`.
+ * Both must produce the same output for the same types, providing a stable reference for
+ * external implementations of the ROS 2 Type Version Hash.
+ *
+ * The JSON representation contains all types and fields of the original message, but excludes:
+ * - Default values
+ * - Comments
+ * - The input plaintext files that generated the TypeDescription
+ *
+ * \param[in] type_description Prefilled TypeDescription message to be translated
+ * \param[out] output_repr An initialized empty char array that will be filled with
+ *   the JSON representation of type_description. Note that output_repr will have a
+ *   terminating null character, which should be omitted from hashing. To do so, use
+ *   (output_repr.buffer_length - 1) or strlen(output_repr.buffer) for the size of data to hash.
+ * \return #RCL_RET_OK on success, or
+ * \return #RCL_RET_ERROR if any problems occur in translation.
+ */
+RCL_PUBLIC
+rcl_ret_t
+rcl_type_description_to_hashable_json(
+  const type_description_interfaces__msg__TypeDescription * type_description,
+  rcutils_char_array_t * output_repr);
+
+/// Calculate the Type Version Hash for a given TypeDescription.
+/**
+ * This function produces a stable hash value for a ROS communication interface type.
+ * For design motivations leading to this implementation, see REP-2011.
+ *
+ * This convenience wrapper calls rcl_type_description_to_hashable_json,
+ * then runs sha256 hash on the result.
+ *
+ * \param[in] msg Prefilled TypeDescription message describing the type to be hashed
+ * \param[out] message_digest Preallocated buffer, to be filled with calculated checksum
+ * \return #RCL_RET_OK on success, or
+ * \return #RCL_RET_ERROR if any problems occur while hashing.
+ */
+RCL_PUBLIC
+rcl_ret_t
+rcl_calculate_type_hash(
+  const type_description_interfaces__msg__TypeDescription * type_description,
+  rosidl_type_hash_t * out_type_hash);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // RCL__TYPE_HASH_H_

rcl/package.xml

@@ -19,6 +19,7 @@
 
   <build_export_depend>rmw</build_export_depend>
 
+  <depend>libyaml_vendor</depend>
   <depend>rcl_interfaces</depend>
   <depend>rcl_logging_interface</depend>
   <depend>rcl_logging_spdlog</depend> <!-- the default logging impl -->
@@ -28,6 +29,8 @@
   <depend>rosidl_runtime_c</depend>
   <depend>service_msgs</depend>
   <depend>tracetools</depend>
+  <depend>type_description_interfaces</depend>
+  <depend>yaml</depend>
 
   <test_depend>ament_cmake_gtest</test_depend>
   <test_depend>ament_lint_auto</test_depend>