ZMQ Message Library

[astronomerdave]

I wrote a stand-alone ZMQ message library to replace the daemon server sockets. I've been wanting to do this for awhile because I think it will help NGPS inter-daemon communication reliability, and it makes sense (to me) that camera2 daemon uses the new method.

This is a header-only library.

It currently defines Message::Server and Message::Client which use the ROUTER-DEALER pattern.

I will eventually move my existing Common::PubSub class (currently only in NGPS) from common.h to this message.h

The Network code remains in the repo because it is needed for other things (like Archon communication, for example).

[astronomerdave]

Some of the indentation is a little funny, and some of the comments might be not quite right, but those are because I was trying to make changes only where necessary to show what little of camerad had to be changed (if I had properly indented code then a lot of lines would have been flagged as changed, obscuring the meaningful changes).

[prkrtg]

My recommendation would be to have some sort of Message class

class Message {
public:
    std::string id;
    std::string type;
    std::string payload;
};

That will allow us to shift the message from
[routing][message_id][payload] to serialized messages [routing][message_id][serialized message]

That will allow us to not have to parse for things like

ACK
DONE
ERROR something bad

So we can use type

REQUEST
ACK
DONE
ERROR
PING
PONG
PROGRESS
EVENT

and then our payload would be

{
  "id": "42",
  "type": "DONE",
  "payload": "focus set to 2.5"
}

then we go from if (payload==Message::MSG_PING) to if (msg.type == "PING")

[astronomerdave]

That's a great idea.