[zeromq-dev] 3.x zmq_msg_t change proposal

[Martin Sustrik]

Hi Chuck,

> While thinking through a few scenarios with DEALER/ROUTER (and
> XREQ/XREP) in 0mq 3.0, it occurred to me that it doesn't make a lot
> of sense for us to test the *socket* to see if a message part is a
> label or not. The zmq_msg_t structure already has this information.

The problem is with zmq_send (void*, size_t, int) and zmq_recv (void*, 
size_t, int) There's no way to return the ancillary data using these 
functions.

I wanted to avoid POSIX-like ancillary data:

http://rfc-ref.org/RFC-TEXTS/3542/chapter20.html

If you are familiar with that API, you can see it's much more complex 
that current 0MQ's getsockopt() API.

In short, you can implement access to message flags via message object, 
however, the old way of accessing it is still necessary.

One additional concern: The change is not backward compatible. Current 
implementation clears the flags when receiving a message part. Ie. when 
you re-send it, it behaves like a separate message. It would be nice to 
get rid of this behaviour, however, you need a consensus of users on the 
backward incompatible change.

Martin