You could send a zero length message with no (SND_MORE) flag to signify that’s the last part.

From: zeromq-dev <zeromq-dev-bounces@lists.zeromq.org> On Behalf Of Al Grant
Sent: 08 August 2018 12:56
To: zeromq-dev@lists.zeromq.org
Subject: [zeromq-dev] Abandon a multipart message?

Is there a way to abandon a multipart message if for some reason

I can't complete sending all the parts? I.e.:

   zmq_send(pubsock, ... ZMQ_SNDMORE)

   ... decide I don't want to send the rest of the message ...

   zmq_abandon(pubsock);   // does this exist

Without this, there's a risk that the next message sent - either a

single-part message with flags 0 or the first part of a multipart

message with ZMQ_SNDMORE - would be interpreted as the later

part of a multipart message.

An alternative way to do this would be to introduce a new send

flag meaning "first (or only) part of a message". If seen while

ZMQ_SNDMORE is outstanding it would abandon the previous

multipart message and release its resources (including calling

free-functions). This would be upwards compatible - flags 0 would

have its current meaning - but it would provide extra robustness

and the new ability to abandon sending multipart messages.

At the risk of bikeshedding, I'd suggest a flag ZMQ_SNDFIRST,

then ZMQ_SNDSINGLE could be an alias, with ZMQ_SNDMULTI

being defined as (ZMQ_SNDFIRST|ZMQ_SNDMORE).

Al