4.3.x : segfault on sending data from XSUB to XPUB

[freemanix]

Starting with libzmq 4.3.0, this code crashes:

int main()
{
    zmq::context_t ctx;

    zmq::socket_t publisher(ctx, ZMQ_XPUB);
    publisher.bind("inproc://test");

    zmq::socket_t receiver(ctx, ZMQ_XSUB);
    receiver.connect("inproc://test");

    zmq::message_t subscribe(1);
    *static_cast<unsigned char *>(subscribe.data()) = 2;
    receiver.send(subscribe);

    zmq::message_t receive;
    publisher.recv(&receive);

    return 0;
}

Note that instead of activating subscription (1) or cancelling it (0), I simply send user data (2). The problem is that this code for handling user messages comming upstream never executes:

libzmq/src/xpub.cpp

Lines 114 to 123 in c737e57

	} else {
	// Process user message coming upstream from xsub socket
	_pending_data.push_back (blob_t (msg_data, sub.size ()));
	if (metadata)
	metadata->add_ref ();
	_pending_metadata.push_back (metadata);
	_pending_flags.push_back (sub.flags ());
	sub.close ();
	continue;
	}

Instead, the above else is activated, but it just skip the data processing if first byte is not 0 or 1. Also, this else kind of duplicates above if.

As a result, my code which needs to send upstream data from XSUB to XPUB does not work with libzmq 4.3.0 or higher. Any way how to resolve this?

[bluca]

Thanks for the report, regression introduced by #3168 PR pending