messaging.md

Click messaging

Example messages

See Current protobuf schema for overview examples, and c++ and python tests for detailed examples, ie C++ ControlMessage example and [../python-src/tests/test_messaging.py].

Message structure

• Message
  • ControlMessage - from client only
  • SensorMessage - from sensor only
  • ResetMessage - from either
  • HandshakeInitMessage - from client only
  • HandshakeMessage - from server only
  • ErrorMessage - from server if bad version

Significant Classes

• Message
  • HandshakeInitMessage
  • HandshakeMessage
  • ControlMessage
  • SensorMessage
  • ResetMessage
  • ErrorMessage ...
• MessageSerializer: parses Message --> Bytes, and Bytes --> Message, ie parse(bytes):Message, serialize(message): Bytes
• *MessageBuilder - create Complex Messages
• MessageFactory - create Simple Messages

Technolocy and Design Choices

• 0MQ is an obvious choice to start with because of
  • it's simplicity
  • no middleware needed
  • L-GPL licence with link exception
  • Support for IPC communication
• Handshake vs configuration file
  • Using OpenPLX on controller side
    • Adds unwanted effort and binary size
    • Impose using OpenPLX instead of urdf
  • Starting with a handshake as opposed to a configuration file.
    • Reading another configuration file which also needs to be shared is more complex.
• Protobuf vs flatbuffers
  • Not a strong preference, choosing to start with protobuf mainly because of
    • adoption
    • simplicity.
• Specify units in protocol.
  • Not to start with, specified outside for now.