Bug in ros::NodeHandle::searchParam()?

edit

Hi all,

according to my understanding of searchParam(), the second if condition in the following code snippet should never be true (probably except for some rare race condition cases which shouldn't happen in my case):

  std::string full_param_name, param_name = "a/b";
  if (nh.searchParam(param_name, full_param_name)) {
    if (!nh.getParam(full_param_name, result)) {
      // this should never be reached (but it is reached) ... ?!
    }
  }

In particular, see also this ROS tutorial (wiki).

However, in my case I have /a/b on the parameter server (note the leading / -> global) and param_name is a/b (note the / in between: is this allowed?). searchParam() returns true in that case but getParam() returns false. The ros::NodeHandle nhis initialized with ~ (and, thus, points the node's private namespace). Interesstingly, full_param_name is (erroneously) set to $fully_qualified_namespace_of_my_node/a/b (which doesn't exist).

Is this a bug or am I doing something wrong? Even if "nested keys" (= the / in between a and b) are not allowed (are they?), I would assume that searchParam() returns false ... ?

Thanks!

EDIT: here is a minimum working example that demonstrates the issue:

#include <ros/ros.h>

int main(int argc, char **argv)
{
  ros::init(argc, argv, "test_node");
  std::string full_param_name, param_name = "a/b", result;
  ros::NodeHandle nh("~");
  ros::spinOnce(); // (probably not needed)
  if (nh.searchParam(param_name, full_param_name)) {
    if (!nh.getParam(full_param_name, result)) {
      ROS_FATAL("THIS SHOULD NEVER BE PRINTED ... ?! (%s)", full_param_name.c_str());
    } else {
      ROS_INFO("Okay, parameter found: '%s' = '%s'.", param_name.c_str(), result.c_str());
    }
  } else {
    ROS_INFO("Okay, parameter '%s' not found on the ROS parameter server.", param_name.c_str());
  }
  ros::shutdown(); // (probably not needed)
  return 0;
}

Output:

[FATAL] [1507900407.659972647] [/my_namespace/my_node | 7f61d64c4780]: THIS SHOULD NEVER BE PRINTED ... ?! (/my_namespace/my_node/a/b)

Note that rosparam list | grep "a/b" returns /a/b.

EDIT2: since I am successfully using "nested keys" in my code (at other locations/contexts), I assume that they are allowed.

EDIT3 (@Dirk Thomas): thanks for your assistance / thoughts! I think that I've tracked down the problem correctly now. Your link was somewhat helpful. For instance, assume the following is stored on the parameter server

/a/b: 42
/a/c: 'cannot be found with searchParam using private ns'
/node_namespace/node_name/a/b: 41

and I ask for searchParam(nh_private, "a/b", x) then x=/node_namespace/node_name/a/b (with value 41) and true is returned (all fine). However, if I ask for searchParam(nh_private, "a/c", x) then x=/node_namespace/node_name/a/c and true (sic!) is returned but that parameter does not exist (and I don't understand why the docblock states "[...] (yet)"). IMHO, this behavior of searchParam() makes absolutely no sense and I would consider this to be a bug.

More specifically, my concerns are:

• searchParam() returns true although nothing was found (/node_namespace/node_name/a/c).
• searchParam() is said "to search up the tree for a parameter" but it returns an invalid key although there is a (here: global) parameter (/a/c) matching the given partial key (a/c).

What do you think? ;-)