0MQ version 4.3.5 stable, released on 2023/10/09

• Relicensing from LGPL-3.0+ (with custom exceptions) to MPL-2.0 is now complete.
  libzmq is now distributed under the Mozilla Public License 2.0. Relicensing
  grants have been collected from all relevant authors, and some functionality
  has been clean-room reimplemented where that was not possible. In layman terms,
  the new license provides the same rights and obligations as before. Source
  files are now tagged using the SPDX license identifier format.
  Details of the relicensing process can be seen at:
  https://github.com/zeromq/libzmq/issues/2376
  Relicensing grants have been archived at:
  https://github.com/rlenferink/libzmq-relicense
  A special thanks to everybody who helped with this long and difficult task,
  with the process, the reimplementations, the collections and everything else.

• New DRAFT (see NEWS for 4.2.0) socket options:

  • ZMQ_BUSY_POLL will set the SO_BUSY_POLL socket option on the underlying
    sockets, if it is supported.
  • ZMQ_HICCUP_MSG will send a message when the peer has been disconnected.
  • ZMQ_XSUB_VERBOSE_UNSUBSCRIBE will configure a socket to pass all
    unsubscription messages, including duplicated ones.
  • ZMQ_TOPICS_COUNT will return the number of subscribed topics on a
    PUB/SUB socket.
  • ZMQ_NORM_MODE, ZMQ_NORM_UNICAST_NACK, ZMQ_NORM_BUFFER_SIZE,
    ZMQ_NORM_SEGMENT_SIZE, ZMQ_NORM_BLOCK_SIZE, ZMQ_NORM_NUM_PARITY,
    ZMQ_NORM_NUM_AUTOPARITY and ZMQ_NORM_PUSH to control various aspect of
    NORM sockets.
    See doc/zmq_setsockopt.txt and doc/zmq_getsockopt.txt for details.

• New DRAFT (see NEWS for 4.2.0) zmq_ppoll APIs was added that differs from
  zmq_poll in the same way that ppoll differs from poll.
  See doc/zmq_ppoll.txt for details.

• Various bug fixes and performance improvements.