[zeromq-dev] Not receiving unsubscription messages in XPUB socket with ZMQ_XPUB_VERBOSE when using a proxy

Ricardo Catalinas Jiménez jimenezrick at gmail.com
Tue Jul 21 14:13:10 CEST 2015

On Tue, Jul 21, 2015 at 08:02:54AM -0400, Brian Knox wrote:
> Ricardo - if you are lucky, there might be a loophole here for you to
> exploit with a little lawyering.
> "This is my preferred solution although it could break applications
> that subscribe multiple times to the same topic and expect to stop
> receiving messages only when they unsubscribe the same number of
> times.  Although I'm not aware that this behavior is documented
> which could mean it isn't really a problem."

Well, unfortunately it's documented, so any change on this would break
the contract fo the current API. Although I don't find much value in
this behavior because it just add complexity, this is what the current
doc says:


"If the socket has several instances of the same filter attached the
ZMQ_UNSUBSCRIBE option shall remove only one instance, leaving the rest
in place and functional."

Which implicitly is referring to the reference counting happening
underneath. So, unless someone with authority says we should modify
this, I guess it's something we shouldn't touch.

> Do you know if there is a specific test case for this behavior?  If your
> change changes this behavior but does not break the test suite, I believe
> it might be accepted.  One of the guiding principals for ZeroMQ development
> is, paraphrased, "if you liked it should have put a test around it".  "A
> breaking change" is usually interpreted to mean "it breaks the tests" (note
> it's the wording Pieter used in his response).  If this behavior is not
> documented and it is not tested you should be in good shape, as far as I
> know.


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