[zeromq-dev] Purpose of empty frame in MDP 0.1

Pieter Hintjens ph at imatix.com
Wed Jan 14 13:44:14 CET 2015

The empty frame was there only for convention, to emulate the REP/REQ
envelope. It's superfluous and confusing and so got removed at some
stage. You can't actually implement realistic clients using REQ/REP
since you need heartbeating.

On Wed, Jan 14, 2015 at 1:48 AM, André Caron <andre.l.caron at gmail.com> wrote:
> Hi all,
> In the MDP 0.1 (RFC 7) spec, all messages begin with a 0-length frame.  In
> the MDP 0.2 spec (RFC 18), this empty frame is no longer accepted so I
> started wondering why it was there in the original spec and if removing it
> breaks anything.
> I always thought this empty frame was used as a delimiter (as in chapter 3
> of the guide) so that the message return addresses can be stacked, but in
> hindsight it seems a bit weird that in RFC 7, the message frames are
> explicitly numbered.
> So, was the empty frame expected to serve this purpose or was it merely
> there for convention?
> Thanks!
> André
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