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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)