[zeromq-dev] Multi-part messages

Martin Sustrik sustrik at 250bpm.com
Sat Mar 27 19:00:26 CET 2010


Hi Brian,

>> No API for it now. I have no sane idea how the API should look like :(
>>
>> As an workaround you can check the flag by hand:
>>
>> zmq_msg_t msg;
>> ...
>> int tbc = msg.flags & ZMQ_MSG_TBC ? 1 : 0;
> 
> I guess this is the API then :)  I will think about how to represent
> this in Python.

Any idea is welcome. I've made up a list of requirements to figure out 
how the API should look like:

1. When multi-part messages are not used, the API should be 100% 
backward compatible. In other words, those not using multi-part messages 
shouldn't be required to have a slightest idea about it.

2. When forwarding messages, message part boundaries should be retained:

    while (true) {s1.recv (&msg); s2.send (msg);}

In other words, TBC flag should be part of the message rather than part 
of the zmq_send/zmq_recv invocation.

Another consequence is that zmq_msg_move and zmq_msg_copy should copy 
the TBC flag.

3. Generic requirement: We should avoid API creep; it not possible we 
should use generic extension points rather than single-purpose constructs.

The only solution that matches the above criteria I was able to think of 
was zmq_setmsgopt, zmq_getmsgopt and ZMQ_TBC message option. Still, it 
seems rather complex... The BSD alternative is ancillary data which is 
pretty hideous API itself...

Thoughts?
Martin



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