Better error reporting from server

[jpreiss]

The Crazyswarm server sometimes fails with an uninformative error message, see e.g. #379. More informative error messages could help reduce the Q&A load.

[jpreiss]

1e1c2b1 also for this issue

[jpreiss]

A big one is integer values in crazyflies.yaml initialPosition coordinates. This causes an XmlRpcException, but not from here:

crazyswarm/ros_ws/src/crazyswarm/src/crazyswarm_server.cpp

Line 1183 in b4641e7

nGlobal.getParam("crazyflies", crazyflies);

I ran out of time to investigate today, but maybe the exception is happening in the rosparam node?

[whoenig]

My guess is that this is from

crazyswarm/ros_ws/src/crazyswarm/src/crazyswarm_server.cpp

Line 1201 in b4641e7

ROS_ASSERT(pos[j].getType() == XmlRpc::XmlRpcValue::TypeDouble);

This should probably also allow integers and use a simple assignment in the integer case.

[jpreiss]

Oh, does ROS_ASSERT raise an XmlRpcException? I would not have guessed that...

I agree that accepting integers is a better solution.

[whoenig]

No, ROS_ASSERT probably doesn't raise such an explicit exception:-( Like a normal assert, it's also disabled in release builds. The problem is likely the next line, which calls a cast operator (http://docs.ros.org/en/noetic/api/xmlrpcpp/html/classXmlRpc_1_1XmlRpcValue.html#a95fa5d878b5c5946994b49f02829efc0):

crazyswarm/ros_ws/src/crazyswarm/src/crazyswarm_server.cpp

Line 1202 in b4641e7

double f = static_cast<double>(pos[j]);

I assume we would need a switch/if statement here and handle both the int and double case. Luckily, there are no more other (relevant) types...