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Flipping

Overview

Flipping is a means of getting a local connection across to remote ros system via the gateway network. Note that the flipped connection is not a relay, it is a direct node to node connection where your local node's connection details get registered at the remote master via the instruction of the remote gateway.

Workflow

The usual workflow for a flip is as follows (note that some of these steps are internal, but presented here for illustration):

• You create a flip rule containing the following data:
  • Target remote gateway name (e.g. 'Foobar Gateway')
  • Local connection name (e.g. '/chatter')
  • Local connection type (e.g. 'publisher')
  • Local connection node name (e.g. '/talker')

Note that each of the fields except for type may also be a python regex pattern, e.g. '/chat.*'.

• The flip rule gets added to a watchlist
• If a matching connection is available, it immediately sends a flip request.
• The local gateway periodically checks for matches against the flip rule and acts when it finds a match.

Any flip request is handled by the remote gateway before proceeding.

• If the remote gateway has a firewall flag configured, it blocks, otherwise
• It registers the connection with it's local master.

Code

Some example python code:

   1 gateway = 'Foo Gateway'
   2 flip_service = rospy.ServiceProxy('/gateway/flip',Remote)
   3 gateway = 'Foo Gateway'
   4 req = RemoteRequest()
   5 req.cancel = False
   6 req.remotes = []
   7 rule = gateway_msgs.msg.Rule()
   8 rule.name = '/chatter'
   9 rule.type = gateway_msgs.ConnectionType.PUBLISHER
  10 rule.node = '/talker'
  11 req.remotes.append(RemoteRule(gateway,rule))
  12 rospy.loginfo("Flip : [%s,%s,%s,%s]."%(gateway, rule.name, rule.type, rule.node)
  13 resp = self.flip_service(req)
  14 if resp.result != 0:
  15     rospy.logerr("Flip : %s"%resp.error_message)

Examples

In three separate shells, launch the hub, a gateway system with tutorials running, and an empty gateway system.

> roslaunch --port=11311 rocon_gateway_tutorials pirate_hub.launch

> roslaunch --port=11312 rocon_gateway_tutorials pirate_gateway_tutorials.launch

> roslaunch --port=11313 rocon_gateway_tutorials pirate_gateway.launch

To flip a the publisher /chatter only from the first gateway to the second, in a shell with ROS_MASTER_URI=http://localhost:11312:

> rosrun rocon_gateway_tutorials flip_tutorials --pubonly

Run flip_tutorials with --help to find the other target operations. For more code samples, check the source code of the flip scripts in rocon_gateway_tutorials.

Limitations

Gateways can't remap connection namespaces, beware of conflicts with flips from other gateways. You may need some infrastructure to ensure that you are flipping to a unique namespace on the remote system.

Flipping creates a direct registration/connection. It does not change the type (e.g. tcpros/udpros) of connection made. We are waiting for changes in the communication infrastructure before handling this.