Use namespaces

[wjwwood]

Connects to ros2/rcl#137

Here are some examples of what it looks like when you give invalid names now:

• invalid node name

% python3 -c "import rclpy; rclpy.init(); rclpy.create_node('invalid_node?')"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Users/william/ros2_ws/install/lib/python3.6/site-packages/rclpy/__init__.py", line 38, in create_node
    validate_node_name(node_name)
  File "/Users/william/ros2_ws/install/lib/python3.6/site-packages/rclpy/validate_node_name.py", line 34, in validate_node_name
    raise InvalidNodeNameException(node_name, error_msg, invalid_index)
rclpy.exceptions.InvalidNodeNameException: Invalid node name: node name must not contain characters other than alphanumerics or '_':
  'invalid_node?'
               ^

• invalid node namespace

% python3 -c "
import rclpy
rclpy.init()
rclpy.create_node('node_name', namespace='/invalid_ns?')"
Traceback (most recent call last):
  File "<string>", line 4, in <module>
  File "/Users/william/ros2_ws/install/lib/python3.6/site-packages/rclpy/__init__.py", line 43, in create_node
    validate_namespace(namespace)
  File "/Users/william/ros2_ws/install/lib/python3.6/site-packages/rclpy/validate_namespace.py", line 38, in validate_namespace
    raise InvalidNamespaceException(namespace, error_msg, invalid_index)
rclpy.exceptions.InvalidNamespaceException: Invalid namespace: namespace must not contain characters other than alphanumerics, '_', or '/':
  '/invalid_ns?'
              ^

• invalid topic name

% python3 -c "
import rclpy
from std_msgs.msg import String
rclpy.init()
n = rclpy.create_node('node_name')
n.create_publisher(String, 'chatter?')"
Traceback (most recent call last):
  File "<string>", line 6, in <module>
  File "/Users/william/ros2_ws/install/lib/python3.6/site-packages/rclpy/node.py", line 77, in create_publisher
    self._validate_topic_or_service_name(topic)
  File "/Users/william/ros2_ws/install/lib/python3.6/site-packages/rclpy/node.py", line 60, in _validate_topic_or_service_name
    validate_topic_name(topic_or_service_name, is_service=is_service)
  File "/Users/william/ros2_ws/install/lib/python3.6/site-packages/rclpy/validate_topic_name.py", line 41, in validate_topic_name
    raise InvalidTopicNameException(name, error_msg, invalid_index)
rclpy.exceptions.InvalidTopicNameException: Invalid topic name: topic name must not contain characters other than alphanumerics, '_', '~', '{', or '}':
  'chatter?'
          ^

• invalid service name

% python3 -c "
import rclpy
from std_srvs.srv import Empty
rclpy.init()
n = rclpy.create_node('node_name')
n.create_client(Empty, 'empty?')"
Traceback (most recent call last):
  File "<string>", line 6, in <module>
  File "/Users/william/ros2_ws/install/lib/python3.6/site-packages/rclpy/node.py", line 118, in create_client
    self._validate_topic_or_service_name(srv_name, is_service=True)
  File "/Users/william/ros2_ws/install/lib/python3.6/site-packages/rclpy/node.py", line 60, in _validate_topic_or_service_name
    validate_topic_name(topic_or_service_name, is_service=is_service)
  File "/Users/william/ros2_ws/install/lib/python3.6/site-packages/rclpy/validate_topic_name.py", line 39, in validate_topic_name
    raise InvalidServiceNameException(name, error_msg, invalid_index)
rclpy.exceptions.InvalidServiceNameException: Invalid service name: topic name must not contain characters other than alphanumerics, '_', '~', '{', or '}':
  'empty?'
        ^