Simple library (with reference Python implementation) to do discovery on top of zeromq messaging. This is a modification of the ROS 2.0 zmq prototype to implement messaging + discovery via zmq with serialization handled through binary pickling. Also provides topic synchronization capability through the get_listeners method.

Raw message definitions:

• Header (HDR):

  • VERSION: 2 bytes
  • GUID: 16 bytes; ID that is unique to the process, generated according to RFC 4122
  • TOPICLENGTH: 1 byte; length, in bytes, of TOPIC
  • TOPIC: string; max 192 bytes
  • TYPE: 1 byte
  • FLAGS: 16 bytes (unused for now)

• advertisement (ADV):

  • HDR (TYPE = 1)
  • ADDRESSLENGTH: 2 bytes; length, in bytes, of ADDRESS
  • ADDRESS: one valid ZeroMQ address (e.g., "tcp://10.0.0.1:6000")

• subscription (SUB):

  • HDR (TYPE = 2)
  • ADDRESSLENGTH: 2 bytes; length, in bytes, of ADDRESS
  • ADDRESS: one valid ZeroMQ address (e.g., "tcp://10.0.0.1:6000")

ZeroMQ message definitions (for which we will let zeromq handle framing):

• publication (PUB) multipart messages, with the following parts:
  • TOPIC (placed first to facilitate filtering)
  • BODY: opaque bytes

Defaults and conventions:

• Default port for Broadcast messages: 11312
• By convention, Raw messages are sent to a broadcast address.
• In raw messages, all integers are sent little-endian

API sketch:

• (un)advertise(topic)
• subscribe(topic, cb)
  • cb(msg)
• unsubscribe(topic)
• publish(topic, msg)
• get_listeners(topic)