Service Introspection

[ihasdapie]

This PR is a prototype for the service introspection REP (ros-infrastructure/rep#360) implementing the proposed serialized service event approach.

Few items of note

• This would introduce new dependencies for rcl on rosidl_typesupport_introspection_c and rosidl_typesupport_c
• This implements a rather hacky way of loading the respective Request/Response typesupports given a Service typesupport by inspecting the service typesupport's symbol names to find the service name, then using that to build the name of the Request/Response typesupport libaries and loading them in.
  

  rcl/rcl/src/rcl/introspection.c

  Lines 57 to 119 in 9c0b42e

  	rcl_ret_t
  	rcl_service_typesupport_to_message_typesupport(
  	const rosidl_service_type_support_t * service_typesupport,
  	rosidl_message_type_support_t ** request_typesupport,
  	rosidl_message_type_support_t ** response_typesupport,
  	const rcl_allocator_t * allocator)
  	{
  	rcutils_ret_t ret;
  	type_support_map_t * map = (type_support_map_t *)service_typesupport->data;
  	const char * typesupport_library_fmt = "lib%s__rosidl_typesupport_c.so";
  	const char * service_message_fmt = // package_name, type name, Request/Response
  	"rosidl_typesupport_c__get_message_type_support_handle__%s__srv__%s_%s";
  	const char * service_type_name = rcl_service_get_service_type_name(service_typesupport);
  	// build out typesupport library and symbol names
  	char * typesupport_library_name = allocator->allocate(
  	sizeof(char) * ((strlen(typesupport_library_fmt) - 2) +
  	strlen(map->package_name) + 1),
  	allocator->state);
  	char * request_message_symbol = allocator->allocate(
  	sizeof(char) *
  	((strlen(service_message_fmt) - 6) + strlen(map->package_name) +
  	strlen(service_type_name) + strlen("Request") + 1),
  	allocator->state);
  	char * response_message_symbol = allocator->allocate(
  	sizeof(char) *
  	((strlen(service_message_fmt) - 6) + strlen(map->package_name) +
  	strlen(service_type_name) + strlen("Request") + 1),
  	allocator->state);
  	sprintf(typesupport_library_name, typesupport_library_fmt, map->package_name);
  	sprintf(request_message_symbol, service_message_fmt, map->package_name,
  	service_type_name, "Request");
  	sprintf(response_message_symbol, service_message_fmt, map->package_name,
  	service_type_name, "Response");
  	rcutils_shared_library_t typesupport_library = rcutils_get_zero_initialized_shared_library();
  	ret = rcutils_load_shared_library(&typesupport_library, typesupport_library_name, *allocator);
  	if (RCUTILS_RET_OK != ret) {
  	return RCL_RET_ERROR;
  	}
  	rosidl_message_type_support_t *(*req_typesupport_func_handle)() =
  	(rosidl_message_type_support_t * (*)())
  	rcutils_get_symbol(&typesupport_library, request_message_symbol);
  	RCL_CHECK_FOR_NULL_WITH_MSG(req_typesupport_func_handle,
  	"Looking up request type support failed", return RCL_RET_ERROR);
  	rosidl_message_type_support_t *(*resp_typesupport_func_handle)() =
  	(rosidl_message_type_support_t * (*)())
  	rcutils_get_symbol(&typesupport_library, response_message_symbol);
  	RCL_CHECK_FOR_NULL_WITH_MSG(resp_typesupport_func_handle,
  	"Looking up response type support failed", return RCL_RET_ERROR);
  	*request_typesupport = req_typesupport_func_handle();
  	*response_typesupport = resp_typesupport_func_handle();
  	allocator->deallocate(typesupport_library_name, allocator->state);
  	allocator->deallocate(request_message_symbol, allocator->state);
  	allocator->deallocate(response_message_symbol, allocator->state);
  	return RCL_RET_OK;
  	}

• The client_id is not populated on client send request events due to the writer_guid not being accessible from the client_send_request scope. PRs will be made to the rmw implementations to make this accessible.
• There are no tests/docs/minimal error handling. It also definitely doesn't pass linting and there are superfluous #includes. I will fix this later :)

For instructions on how to build and run this see the meta-ticket ros2/ros2#1285

Resolves ros2/ros2#1285

[clalancette]

• This would introduce new dependencies for rcl on rosidl_typesupport_introspection_c and rosidl_typesupport_c

I just took a quick look, and it looks like there is already an (build) indirect dependency between rcl and rosidl_typesupport_introspection_c/rosidl_typesupport_c:

rcl -> rcl_interfaces -> rosidl_default_generators -> rosidl_typesupport_introspection_c (same goes for rosidl_typesupport_c). Thus I think turning this into a direct dependency is fine.

[ivanpauno]

partial review

[jacobperron]

The approach looks good to me. Besides the string manipulation related to service typesupport, the code looks straight-forward 👍 I also agree with Ivan's comments.

I realize you haven't focused on error handling yet, but when you do you should look out for the following (which might help uncover bugs downstream):

1. Always check the return values of functions (this isn't happening in many places)
2. Make sure to do any necessary memory deallocation before returning from functions (pay attention to places where you are returning early due to an error).
3. Check arguments to functions before using them (e.g. if they are null or invalid).

[ihasdapie]

Closing in lieu of #997 to keep all service introspection work under a single branch name

[ivanpauno]

@ihasdapie I think you meant to close this PR (replaced with #997), so I'm closing it now.
Please, reopen if that was not the case.

[ihasdapie]

@ivanpauno Yup, thanks! I had forgotten.