PubSub (De)MultiPlexers

These classes allow a regular nanomsg pubsub system to be mux’d on the publisher side and demux’d on the subscriber side. On most systems you wouldn’t worry about it (c.f. ros which creates a port for every pub/sub connection), however for embedded systems this gets expensive - the extra creation of ports does get somewhat costly.

Overview

• Use a packet id (unsigned int) for each type of publication.
• Decoupled marshalling code in message_multiplexing::Message classes.
• Mux and demux registered with a name/url pair. Pubs and subs connect by name.
• Publishers can publish from anywhere.
• Only one subscriber per packet id

Classes

• Message : basic serialiser/deserialiser for a particular message type
• Publisher : can publish any/all packet types
• Subscriber : single packet type receiver which will convert a received buffer and relay to a user callback
• MessageRegistry : global enabler for managing the mux/demux’s and their connection with pubs/subs.

Socket Address Types

• IntraProcess : inproc://a
• InterProcess : ipc:///tmp/test.ipc
• InterPC : tcp://server001:5560

Roadmap

Todos:

• zero-copy buffer allocations via nn_allocmsg for nanomsg transport
• as reduce cost of resizing buffers on the way in via the publisher (spec. for images, maybe c++11 std::move?)
• transports - mux and demux should separate the actual underlying transport (nanomsg/serial…)
• handle use case in which packets are gathered and sent (e.g. kobuki style)
• optional flag when sending that belays the send.
• split packet signature from packet id/payload length
• loadable { packet_id : data_type } registries for pubs and subs to check against
• switch to ecl byte array converters in impl/builders.hpp
• mux should create muxes on the fly like demux
• ~~publisher to encode, then send a buffer to the mux which relays across the wire ~~
• convert the builders to specific Message class types with encode/decode functionality

Maybe dos:

• Relax the one subscriber per packet id constraint.

Testing

You can test the subscriber end of a connection without programming using nanocat. An example:

> nanocat --sub --connect tcp://192.168.1.3:5555 --ascii

Changelog

0.2.0 (2014-09-17)

• nanomsg pipeline and service demo programs
• mux/demux static api renamed to allow cross-class templatisation calls

0.1.1 (2014-09-12)

• publisher and subscriber frontends.
• multiplexer and demultiplexer.