ZMQ_XPUB_VERBOSE backward compatibility broken in 4.2

[kikosha]

In zmq_setsockopts API v4.1 it says:

ZMQ_XPUB_VERBOSE: provide all subscription messages on XPUB sockets
Sets the XPUB socket behavior on new subscriptions and unsubscriptions. A value of 0 is the default and passes only new subscription messages to upstream. A value of 1 passes all subscription messages upstream.

In zmq_setsockopts API v4.2 it says:

ZMQ_XPUB_VERBOSE: pass subscribe messages on XPUB socket
Sets the XPUB socket behaviour on new subscriptions. If enabled, the socket passes all subscribe messages to the caller. If disabled, these are not visible to the caller. The default is 0 (disabled).

Obviously, this breaks the backward compatibility

[bluca]

Hi,

The old documentation for the option was misleading and was changed in #1786 . That option does not affect the passing of new subscriptions - that always happened, as it's the reason of the existence of XPUB vs a simple PUB.

As you can see in the code new subs are always passed:

https://github.com/zeromq/libzmq/blob/master/src/xpub.cpp#L122

if (options.type == ZMQ_XPUB && (unique || (*data == 1 && verbose_subs) ||
      (*data == 0 && verbose_unsubs && verbose_subs))) {

If you find the new wording to be confusing as well, please feel free to send a PR to amend it and make it clearer. Meanwhile, given there is no backward incompatibility I'll close this issue to avoid confusion.

[bluca]

Upon further review, there is space for improving the current docs. Will push changes soon that will clarify that these options only affect duplicates.