0MQ version 4.1.8 stable, released on 2020/09/07
================================================

* Security advisories:
  * CVE-2020-15166: Denial-of-Service on CURVE/ZAP-protected servers by
    unauthenticated clients.
    If a raw TCP socket is opened and connected to an endpoint that is fully
    configured with CURVE/ZAP, legitimate clients will not be able to exchange
    any message. Handshakes complete successfully, and messages are delivered to
    the library, but the server application never receives them.
    For more information see the security advisory:
    https://github.com/zeromq/libzmq/security/advisories/GHSA-25wp-cf8g-938m
  * Stack overflow on server running PUB/XPUB socket (CURVE disabled).
    The PUB/XPUB subscription store (mtrie) is traversed using recursive
    function calls. In the remove (unsubscription) case, the recursive calls are
    NOT tail calls, so even with optimizations the stack grows linearly with the
    length of a subscription topic. Topics are under the control of remote
    clients - they can send a subscription to arbitrary length topics. An
    attacker can thus cause a server to create an mtrie sufficiently large such
    that, when unsubscribing, traversal will cause a stack overflow.
    For more information see the security advisory:
    https://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8
  * Memory leak in client induced by malicious server(s) without CURVE/ZAP.
    When a pipe processes a delimiter and is already not in active state but
    still has an unfinished message, the message is leaked.
    For more information see the security advisory:
    https://github.com/zeromq/libzmq/security/advisories/GHSA-wfr2-29gj-5w87


0MQ version 4.1.7 stable, released on 2019/07/08
================================================

* CVE-2019-13132: a remote, unauthenticated client connecting to a
  libzmq application, running with a socket listening with CURVE
  encryption/authentication enabled, may cause a stack overflow and
  overwrite the stack with arbitrary data, due to a buffer overflow in
  the library. Users running public servers with the above configuration
  are highly encouraged to upgrade as soon as possible, as there are no
  known mitigations. All versions from 4.0.0 and upwards are affected.

* Fixed #2254 - zmq 4.1.6 cannot pub msg to a zmq 2.x

* Fixed #2623 - ZMQ_ROUTER: with ZMQ_ROUTER_MANDATORY, ZMQ_POLLOUT will now
                now return true only if at least one pipe is ready for writing

* Fixed #159 - off-by-one error leaves ZMQ_STREAM unusable

* Fixed #163 - Fix divide by zero, in case of race condition, with ZMQ_PUSH

* Fixed #164 - EHOSTDOWN socket error assertion

* Fixed #165 - inproc pub/sub does not work when sub connects/binds before pub
               does

* Fix parsing application metadata when using CURVE


0MQ version 4.1.6 stable, released on 2016/11/01
================================================

* Fixed #2051 - getifaddrs can fail with ECONNREFUSED

* Fixed #2091 - testutil.hpp fails to build on Windows XP

* Fixed #2096 - add tests/CMakeLists.in and version.rc.in to dist tar

* Fixed #2107 - zmq_connect with IPv6 "source:port;dest:port" broken

* Fixed #2117 - ctx_term assert with inproc zmq_router connect-before-bind

* Fixed #2158 - Socket monitor uses internal Pair from multiple threads

* Fixed #2161 - messages dropped due to HWM race

* Fixed #1325 - alignment issue with zmq_msg_t causes SIGBUS on SPARC and ARM


0MQ version 4.1.5 stable, released on 2016/06/17
================================================

* Fixed #1673 - CMake on Windows put PDB in wrong directory.

* Fixed #1723 - Family is not set when resolving NIC on Android.

* Fixed #1608 - Windows 7 TCP slow start issue.

* Fixed #1806 - uninitialised read in curve getsockopt.

* Fixed #1807 - build broken with GCC 6.

* Fixed #1831 - potential assertion failure with latest libsodium.

* Fixed #1850 - detection issues with tweetnacl/libsodium.

* Fixed #1877 - Avoid terminating connections prematurely

* Fixed #1887 - zmq_bind IPv4 fallback still tries IPv6

* Fixed #1866 - fails to build on SunOS 5.10 / Solaris 10

* Fixed #919 - ZMQ_LINGER (related to #1877)

* Fixed #114 - cannot unbind with same endpoint with IPv6 enabled.

* Fixed #1952 - CMake scripts not part of release tarballs

* Fixed #1542 - Fix a crash on Windows when port 5905 is in use.

* Fixed #2021 - Fix building on sparc32.


0MQ version 4.1.4 stable, released on 2015/12/18
================================================

* Fixed #1315 - socket monitor hangs if bind/setsockopt failed.

* Fixed #1399 - assertion failure in tcp.cpp after network reconnect.

* Fixed #1632 - build failure using latest libsodium.

* Fixed #1644 - assertion failure in msg.cpp:390 on STREAM sockets.

* Fixed #1661 - does not handle IPv6 link local addresses.


0MQ version 4.1.3 stable, released on 2015/08/17
================================================

* Fixed #1532 - getsockopt ZMQ_RCVMORE now resets all bits instead of only 32

* Fixed #1445 - zmq::socket_base_t::connect fails on tcp ipv6 address


0MQ version 4.1.2 stable, released on 2015/06/15
================================================

* Added explicit reference to static link exception in every source file.

* Bumped ABI version to 5:0:0 since 4.1.x changed the ABI.

* Fixed STDINT event interface macros to work with CZMQ 3.0.

* Fixed installation of man pages when BUILD_DOC is not set.

* Fixed #1428 - regression on single-socket proxies.


0MQ version 4.1.1 stable, released on 2015/06/02
================================================

* Fixed #1208 - fix recursion in automake packaging.

* Fixed #1224 - crash when processing empty unsubscribe message.

* Fixed #1213 - properties files were missing from source packages.

* Fixed #1273 - V3 protocol handler vulnerable to downgrade attacks.

* Fixed #1347 - lack way to get peer address.

* Fixed #1362 - SUB socket sometimes fails to resubscribe properly.

* Fixed #1377, #1144 - failed with WSANOTINITIALISED in some cases.

* Fixed #1389 - PUB, PUSH sockets had slow memory leak.

* Fixed #1382 - zmq_proxy did not terminate if there were no readers.


0MQ version 4.1.0 rc1, released on 2014/10/14
=============================================

* All issues that were fixed in 4.0.x

* Improved client reconnection strategy on errors

* GSSAPI security mechanism

* SOCKS5 support (ZMQ_SOCKS_PROXY)

* ZMQ_ROUTER_HANDOVER

* ZMQ_TOS

* ZMQ_CONNECT_RID

* ZMQ_HANDSHAKE_IVL

* ZMQ_IDENTITY_FD

* ZMQ_XPUB_NODROP

* ZMQ_SRCFD and ZMQ_SHARED message options

* Message metadata -- zmq_msg_gets ()

* Probe library configuration -- zmq_has ()


0MQ version 4.0.5 stable, released on 2014/10/14
================================================

* Fixed #1191; CURVE mechanism does not verify short term nonces.

* Fixed #1190; stream_engine is vulnerable to downgrade attacks.

* Fixed #1088; assertion failure for WSAENOTSOCK on Windows.

* Fixed #1015; race condition while connecting inproc sockets.

* Fixed #994; bump so library number to 4.0.0

* Fixed #939, assertion failed: !more (fq.cpp:99) after many ZAP requests.

* Fixed #872; lost first part of message over inproc://.

* Fixed #797, keep-alive on Windows.


0MQ version 4.0.4 stable, released on 2014/03/10
================================================

Bug Fixes
---------

* Fixed #909; out of tree build issue on Linux.

* Fixed #888; hangs on terminate when inproc connected but never bound.

* Fixed #868; assertion failure at ip.cpp:137 when using port scanner.

* Fixed #818; fix timestamp counter on s390/s390x.

* Fixed #817; only export zmq_* symbols.

* Fixed #797; fixed setting TCP keepalive on Windows.

* Fixed #775; compile error on Windows.

* Fixed #763; when talking to a ZMTP v1 peer (libzmq 2.2), a socket would
  send an extra identity frame at the start of the connection.

* Fixed LIBZMQ-576 - Crash closing a socket after zmq_msg_send returns
  EAGAIN (reverts LIBZMQ-497)

* Fixed LIBZMQ-584; subscription filters getting lost on reconnection.


0MQ version 4.0.3 stable, released on 2013/11/24
================================================

Bug Fixes
---------

* Fixed test_many_sockets case, which failed when process socket limit
  was 1024.


0MQ version 4.0.2 stable, released on 2013/11/24
================================================

Bug Fixes
---------

* Fixed LIBZMQ-583 - improved low-res timer for Windows
* Fixed LIBZMQ-578 - z85_decode was extremely slow
* Fixed LIBZMQ-577 - fault in man pages.
* Fixed LIBZMQ-574 - assertion failure when ran out of system file handles
* Fixed LIBZMQ-571 - test_stream failing in some cases
* Fixed LIBZMQ-569 - Socket server crashes with random client data and when
  talking to 2.2 versions
* Fixed LIBZMQ-39 - Bad file descriptor during shutdown
* Pulled expected failing test_linger.cpp from release
* Reduced pause time in tests to allow "make check" to run faster


0MQ version 4.0.1 stable, released on 2013/10/08
================================================

Changes
-------

* Updated CURVE mechanism to track revised RFC 27 (INITIATE vouch).

  The INITIATE command vouch box is Box[C',S](C->S') instead of
  Box[C'](C->S), to reduce the risk of client impersonation, as per
  https://codesinchaos.wordpress.com/2012/09/09/curvecp-1/.

* Fixed LIBZMQ-567, adding abstract namespaces for IPC sockets on Linux.

  Converts an initial strudel or "at sign" (@) in the Unix socket path to
  a NULL character ('\0') indicating that the socket uses the abstract
  namespace instead of the filesystem namespace.  For instance, binding a
  socket to 'ipc://@/tmp/tester' will not create a file associated with
  the socket whereas binding to 'ipc:///tmp/tester' will create the file
  /tmp/tester. See issue 567 for more information.

* Added zmq_z85_encode and zmq_z85_decode to core libzmq API.

* Added zmq_curve_keypair to core libzmq API.

* Bumped library ABI version to 4:0:1.

Bug fixes
---------

* Fixed some build/test errors on OS/X + Clang++.

* Fixed LIBZMQ-565, typo in code.

* Fixed LIBZMQ-566, dealer-to-router connections sometimes failing.

* Fixed builds for AIX, MSVC 2008, OS/X with clang++, Solaris.

* Improved CURVE handshake error handling.


0MQ version 4.0.0 (RC1), released on 2013/09/20
===============================================

Major changes
-------------

* New wire level protocol, ZMTP/3.0, see http://rfc.zeromq.org/spec:23.
  Does not yet implement the SUBSCRIBE, CANCEL, PING, and PONG commands.

* New security framework, from plain user+password to strong encryption,
  see section below. See http://hintjens.com/blog:49 for a tutorial.

* New ZMQ_STREAM socket type for working as a TCP client or server. See:
  tests/test_stream.cpp.

Improvements
------------

* You can now connect to an inproc:// endpoint that does not already
  exist. This means inproc:// no longer needs careful set-up, but it may
  break code that relied on the old behaviour. See:
  tests/test_inproc_connect.cpp.

* Libzmq now checks socket types at connection time, so that trying to
  connect a 'wrong' socket type will fail.

* New zmq_ctx_shutdown API method will shutdown a context and send ETERM
  to blocking calls, without blocking. Use zmq_ctx_term to finalise the
  process.

* The regression test suite has been significantly extended and improved.

* Contexts can now be terminated in forked child processes. See:
  tests/test_fork.cpp.

* zmq_disconnect now respects the linger setting on sockets.

* New zmq_send_const API method to send constant data (without copying).
  See: tests/test_inproc_connect.cpp.

* Added CMake support for static libraries.

* Added test cases for socket semantics as defined in RFCs 28, 29, 30, 31.
  See: tests/test_spec_*.cpp.

* New socket option, ZMQ_PROBE_ROUTER triggers an empty message on connect.
  See: tests/test_probe_router.cpp.

* New socket option, ZMQ_REQ_CORRELATE allows for correlation of replies
  from a REP socket. See: tests/test_req_correlate.cpp.

* New socket option, ZMQ_REQ_RELAXED, lets you disable the state machine
  on a REQ socket, so you can send multiple requests without waiting for
  replies, and without getting an EFSM error. See:
  tests/test_req_relaxed.cpp.

* New socket option, ZMQ_CONFLATE restricts the outgoing and incoming
  socket buffers to a single message. See: tests/test_conflate.cpp.

Deprecated Options
------------------

* ZMQ_IPV4ONLY deprecated and renamed to ZMQ_IPV6 so that options are
  consistently "off" by default.

* ZMQ_DELAY_ATTACH_ON_CONNECT deprecated, and renamed to ZMQ_IMMEDIATE.
  See: tests/test_immediate.cpp.

Security Framework
------------------

Based on new ZMTP wire level protocol that negotiates a security
"mechanism" between client and server before exchanging any other data.

Security mechanisms are extensible. ZMTP defines three by default:

* NULL - classic ZeroMQ, with no authentication. See
  http://rfc.zeromq.org/spec:23.

* PLAIN - plain-text username + password authentication. See
  http://rfc.zeromq.org/spec:24.

* CURVE - secure authentication and encryption based on elliptic curve
  cryptography, using the Curve25519 algorithm from Daniel Bernstein and
  based on CurveCP's security handshake. See http://rfc.zeromq.org/spec:25,
  http://rfc.zeromq.org/spec:26, and http://curvecp.org.

Authentication is done by pluggable "authenticators" that connect to libzmq
over an inproc endpoint, see http://rfc.zeromq.org/spec:27.

Socket options to configure PLAIN security on client or server:

* ZMQ_PLAIN_SERVER, ZMQ_PLAIN_USERNAME, ZMQ_PLAIN_PASSWORD. See
  tests/test_security_plain.

Socket options to configure CURVE security on client or server:

* ZMQ_CURVE_SERVER, ZMQ_CURVE_PUBLICKEY, ZMQ_CURVE_SECRETKEY,
  ZMQ_CURVE_SERVERKEY. See tests/test_security_curve.cpp.

Socket options to configure "domain" for ZAP handler:

* ZMQ_ZAP_DOMAIN, see tests/test_security_null.cpp.

Support for encoding/decoding CURVE binary keys to ASCII:

* zmq_z85_encode, zmq_z85_decode.

Other issues addressed in this release
--------------------------------------

* LIBZMQ-525 Multipart upstreaming from XSUB to XPUB


0MQ version 3.2.4 stable, released on 2013/09/20
================================================

* LIBZMQ-84  (Windows) Assertion failed: Address already in use at signaler.cpp:80
* LIBZMQ-456 ZMQ_XPUB_VERBOSE does not propagate in a tree of XPUB/XSUB devices
* LIBZMQ-532 (Windows) critical section not released on error
* LIBZMQ-569 Detect OpenPGM 5.2 system library
* LIBZMQ-563 Subscribers sometimes stopped receiving messages (aka LIBZMQ-541)
* LIBZMQ-XXX Added support for Travis Continuous Integration
* LIBZMQ-XXX Several improvements to MSVC support


0MQ version 3.2.3 stable, released on 2013/05/02
================================================

Issues addressed in this release
--------------------------------

* LIBZMQ-526 Assertion failure "Invalid argument (tcp_connecter.cpp:285)"
* LIBZMQ-446 Setting the DSCP bits by default causes CAP_NET_ADMIN error
* LIBZMQ-496 Crash on heavy socket opening/closing: Device or resource busy (mutex.hpp:90)
* LIBZMQ-462 test_connect_delay fails at test_connect_delay.cpp:80
* LIBZMQ-497 Messages getting dropped
* LIBZMQ-488 signaler.cpp leaks the win32 Event Handle
* LIBZMQ-476 zmq_disconnect has no effect for inproc sockets
* LIBZMQ-475 zmq_disconnect does not sent unsubscribe messages


0MQ version 3.2.2 stable, released on 2012/11/23
================================================

Issues addressed in this release
--------------------------------

* LIBZMQ-384 No meta data for ZMQ_EVENT_DISCONNECTED monitor event
* LIBZMQ-414 Error in ARM/Thumb2 assembly (atomic_ptr.hpp)
* LIBZMQ-417 zmq_assert (!incomplete_in) in session_base.cpp 228
* LIBZMQ-447 socket_base_t::recv() packet loss and memory leak at high receiving rate
* LIBZMQ-448 Builds fail on older versions of GCC
* LIBZMQ-449 Builds fail on AIX
* LIBZMQ-450 lt-test_monitor: fails with assertion at test_monitor.cpp:81
* LIBZMQ-451 ZMQ_ROUTER_MANDATORY blocks forever
* LIBZMQ-452 test_connect_delay.cpp:175:12: error: 'sleep' was not declared in this scope
* LIBZMQ-458 lt-test_router_mandatory fails with assertion at test_router_mandatory.cpp:53
* LIBZMQ-459 Assertion failed: encoder (stream_engine.cpp:266
* LIBZMQ-464 PUB socket with HWM set leaks memory
* LIBZMQ-465 PUB/SUB results in 80-90% of CPU load
* LIBZMQ-468 ZMQ_XPUB_VERBOSE & unsubscribe
* LIBZMQ-472 Segfault in zmq_poll in REQ to ROUTER dialog


0MQ version 3.2.1 (RC2), released on 2012/10/15
===============================================

Issues addressed in this release
--------------------------------

* Fixed issue xxx - handle insufficient resources on accept() properly.
* Fixed issue 443 - added ZMQ_XPUB_VERBOSE setsocket option.
* Fixed issue 433 - ZeroMQ died on receiving EPIPE
* Fixed issue 423 - test_pair_tcp hangs
* Fixed issue 416 - socket_base: fix 'va_list' has not been declared error
* Fixed issue 409 - Pub-sub interoperability between 2.x and 3.x.
* Fixed issue 404 - zmq_term can not safely be re-entered with pgm transport
* Fixed issue 399 - zmq_ctx_set_monitor callback is not works properly
* Fixed issue 393 - libzmq does not build on Android (socklen_t signed comparison)
* Fixed issue 392 - Interaction with pyzmq on Android
* Fixed issue 389 - Assertion failure in mtrie.cpp:317
* Fixed issue 388 - tests/test_monitor.cpp has no newline at EOF (causes compile error)
* Fixed issue 387 - "sa_family_t sa_family;" in pgm_socket.cpp is unused variable
* Fixed issue 385 - Rework ZMQ_FAIL_UNROUTABLE socket option to actually work
* Fixed issue 382 - Current libzmq doesn't compile on Android NDK
* Fixed issue 377 - ZeroMQ will not build on Windows with OpenPGM
* Fixed issue 375 - error: unused variable 'sa_family'
* Fixed issue 373 - Unable to build libzmq/zeromq3.x on AIX7
* Fixed issue 372 - Unable to build libzmq/zeromq3.x on HPUX 11iv3
* Fixed issue 371 - Unable to build libzmq/zeromq3.x on RHEL5/SLES10
* Fixed issue 329 - wsa_error_to_errno() calls abort() on WSAEACCES
* Fixed issue 309 - Assertion failed: options.recv_identity (socket_base.cpp:864)
* Fixed issue 211 - Assertion failed: msg_->flags & ZMQ_MSG_MORE (rep.cpp:81)

API changes
-----------

* zmq_device () deprecated and replaced by zmq_proxy ().
* zmq_ctx_set_monitor () replaced by zmq_socket_monitor ().
* ZMQ_ROUTER_BEHAVIOR/ZMQ_FAIL_UNROUTABLE renamed experimentally to
  ZMQ_ROUTER_MANDATORY.


0MQ version 3.2.0 (RC1), released on 2012/06/05
===============================================

Bug fixes
---------

* Fixed issue 264 - Potential bug with linger, messages dropped during
  socket close.

* Fixed issue 293 - libzmq doesn't follow the ZMTP/1.0 spec (did not
  set reserved bits to 0).

* Fixed issue 303 - Assertion failure in pgm_sender.cpp:102.

* Fixed issue 320 - Assertion failure in connect_session.cpp:96 when
  connecting epgm to an invalid endpoint.

* Fixed issue 325 - Assertion failure in xrep.cpp:93, when two sockets
  connect using the same identity.

* Fixed issue 327 - Assertion failure in mtrie.cpp:246, when
  unsubscribing from channel.

* Fixed issue 346 - Assertion failure in signaler.cpp:155, when using a
  closed socket.

* Fixed issue 328 - unsubscribe wrongly clears multiple subscriptions.

* Fixed issue 330 - IPC listener does not remove unix domain stream file
  when terminated.

* Fixed issue 334 - Memory leak in session_base.cpp:59.

* Fixed issue 369 - ROUTER cannot close/reopen while DEALER connected.

Operating systems
-----------------

* Fixed issue 301 - HPUX 11iv2 - build fails, CLOCK_MONOTONIC
  undefined.

* Fixed issue 324 - OS/X - build fails, ECANTROUTE undefined.

* Fixed issue 368 - Solaris / Sun C++ - build fails, no insert method
  in multimap classes.

* Fixed issue 366 - Windows - ports not freed after crash.

* Fixed issue 355 - Windows - build fails, MSVC solution file is out of
  date.

* Fixed issue 331 - FreeBSD 8 and 9 - getaddrinfo fails with
  EAI_BADFLAGS on AI_V4MAPPED flag.

* Fixed issue xxx - Added support for WinCE.

Performance
-----------

* Fixed issue xxx - Implemented atomic operations for ARMv7a (runs 15-20% faster).

API changes
-----------

* Fixed issue 337 - Cleaned-up context API:

    zmq_ctx_new() - create new context (will deprecate zmq_init)
    zmq_ctx_destroy() - destroy context (will deprecate zmq_term)
    zmq_ctx_set() - set context property
    zmq_ctx_get() - get context property

* Fixed issue xxx - Cleaned-up message API:

    zmq_msg_send() - send a message (will deprecate zmq_sendmsg)
    zmq_msg_recv() - receive a message (will deprecate zmq_recvmsg)
    zmq_msg_more() - indicate whether this is final part of message
    zmq_msg_get() - get message property
    zmq_msg_set() - set message property

* Fixed issue xxx - Added context monitoring API:

    zmq_ctx_set_monitor() - configure monitor callback.

* Fixed issue xxx - Added unbind/disconnect API:

    zmq_unbind() - unbind socket.
    zmq_disconnect() - disconnect socket.

* Fixed issue xxx - Added ZMQ_TCP_ACCEPT_FILTER setsockopt() for listening TCP sockets.

* Fixed issue 336 - Removed sys: transport.

* Fixed issue 333 - Added zmq_device function back to API (was removed
  in 3.0).

* Fixed issue 340 - Add support for MAX_SOCKETS to new context API.


OMQ version 3.1.0 (beta), released on 2011/12/18
================================================

General information
-------------------

Based on community consensus, the 0MQ 3.1.x release reverts a number of
features introduced in version 3.0. The major reason for these changes is
improving backward compatibility with 0MQ 2.1.x.

Development of the 0MQ 3.0.x series will be discontinued, and users are
encouraged to upgrade to 3.1.

The 0MQ 3.1.x releases use ABI version 3.

Reverted functionality
----------------------

The following functionality present in 0MQ 3.0 has been reverted:

* Wire format changes. The 0MQ 3.1 wire format is identical to that of 0MQ
  2.1.

* LABELs and COMMANDs have been removed.

* Explicit identies are re-introduced, however they can be used only for
  explicit routing, not for durable sockets.

* The ZMQ_ROUTER and ZMQ_DEALER socket types are once again aliases for
  ZMQ_XREQ and ZMQ_XREP.

New functionality
-----------------

* The zmq_getmsgopt() function has been introduced.

* Experimental IPv6 support has been introduced. This is disabled by
  default, see the zmq_setsockopt() documentation for enabling it.

Other changes
-------------

* The default HWM for all socket types has been set to 1000.

* Many bug fixes.

Building
--------

* The dependency on libuuid has been removed.

* Support for building on Android, and with MSVC 10 has been added.

0MQ version 3.0.0 (alpha), released on 2011/07/12
=================================================

New functionality
-----------------

* A zmq_ctx_set_monitor() API to register a callback / event sink for changes
  in socket state.

* POSIX-compliant zmq_send and zmq_recv introduced (uses raw buffer
  instead of message object).

* ZMQ_MULTICAST_HOPS socket option added. Sets the appropriate field in
  IP headers of PGM packets.

* Subscription forwarding. Instead of filtering on consumer, the
  subscription is moved as far as possible towards the publisher and
  filtering is done there.

* ZMQ_XPUB, ZMQ_XSUB introduced. Allow to create subscription-
  forwarding-friendly intermediate devices.

* Add sockopt ZMQ_RCVTIMEO/ZMQ_SNDTIMEO. Allow to set timeout for
  blocking send/recv calls.

* A new LABEL flag was added to the wire format. The flag distinguishes
  message parts used by 0MQ (labels) from user payload message parts.

* There is a new wire format for the REQ/REP pattern. First, the empty
  bottom-of-the-stack message part is not needed any more, the LABEL
  flag is used instead. Secondly, peer IDs are 32-bit integers rather
  than 17-byte UUIDs.

* The REQ socket now drops duplicate replies.

* Outstanding requests & replies associated with a client are dropped
  when the clients dies. This is a performance optimisation.

* Introduced ZMQ_ROUTER and ZMQ_DEALER sockets. These mimic the
  functionality of ZMQ_ROUTER and ZMQ_DEALER in 0MQ/2.1.x. Guarantees
  backward compatibility for exsiting code.

* Removed dependency on OS socketpair buffer size. No more asserts in
  mailbox.cpp because of low system limit of sockepair buffer size.

API improvements
----------------

* Obsolete constants ZMQ_UPSTREAM and ZMQ_DOWNSTREAM removed. Use
  ZMQ_PUSH and ZMQ_PULL instead.

* Timeout in zmq_poll is in milliseconds instead of microseconds. This
  makes zmq_poll() compliant with POSIX poll()

* ZMQ_MCAST_LOOP removed. There's no support for multicast over
  loopback any more. Use IPC or TCP isntead.

* zmq_send/zmq_recv was renamed zmq_sendmsg/zmq_recvmsg.

* ZMQ_RECOVERY_IVL and ZMQ_RECOVERY_IVL_MSEC reconciled. The new option
  is named ZMQ_RECOVERY_IVL and the unit is milliseconds.

* Option types changed. Most of the numeric types are now represented
  as 'int'.

* ZMQ_HWM split into ZMQ_SNDHWM and ZMQ_RCVHWM. This makes it possible
  to control message flow separately for each direction.

* ZMQ_NOBLOCK renamed ZMQ_DONTWAIT. That makes it POSIX-compliant.

Less is More
------------

* Pre-built devices and zmq_device() removed. Should be made available
  as a separate project(s).

* ZMQ_SWAP removed. Writing data to disk should be done on top of 0MQ,
  on inside it.

* C++ binding removed from the core. Now it's a separate project, same
  as any other binding.

Bug fixes
---------

* Many.

Building
--------

* Make pkg-config dependency conditional.

Distribution
------------

* Removed Debian packaging, which is now available at packages.debian.org
  or via apt-get.


0MQ version 2.2.0 (Stable), released on 2012/04/04
==================================================

Changes
-------

* Fixed issue 349, add send/recv timeout socket options.

Bug fixes
---------

* Fixed issue 301, fix builds on HP-UX 11iv3 when using either gcc or aCC.

* Fixed issue 305, memory leakage when using dynamic subscriptions.

* Fixed issue 332, libzmq doesn't compile on Android NDK.

* Fixed issue 293, libzmq doesn't follow ZMTP/1.0 spec.

* Fixed issue 342, cannot build against zmq.hpp under C++11.


0MQ version 2.1.11 (Stable), released on 2011/12/18
===================================================

Bug fixes
---------

* Fixed issue 290, zmq_poll was using system time instead of monotonic
  clock (Mika Fischer).

* Fixed issue 281, crash on heavy socket creation - assertion failure in
  mutex.hpp:91. (Mika Fischer).

* Fixed issue 273, O_CLOEXEC flag used in ip.cpp:192 is supported only
  on Linux kernels 2.6.27+

* Fixed issue 261, assertion failure in kqueue.cpp:76.

* Fixed issue 269, faulty diagnostic code in 2.1.10.

* Fixed issue 254, assertion failure at tcp_socket.cpp:229 on ENOTCONN.

Changes
-------

* Now builds properly on AIX 6.1 (AJ Lewis).

* Builds using libdcekt on HP-UX (AJ Lewis).

* New upstream OpenPGM maintenance release 5.1.118.

* Enabled debugging on assertion failure on Windows (Paul Betts).


0MQ version 2.1.10 (Stable), released on 2011/10/03
===================================================

Bug fixes
---------

* Fixed issue 140, SWAP failed with assertion failure in pipe.cpp:187
  if the current directory was not writeable. Behavior now is to return
  -1 at zmq_setsockopt in this situation.

* Fixed issue 207, assertion failure in zmq_connecter.cpp:48, when an
  invalid zmq_connect() string was used, or the hostname could not be
  resolved. The zmq_connect() call now returns -1 in both those cases.

* Fixed issue 218, sockets not opened with SOCK_CLOEXEC, causing fork/exec
  to sit on sockets unnecessarily.

* Fixed issue 250, build errors on Windows (Mikko Koppanen).

* Fixed issue 252, assertion failure in req.cpp:87 and req.cpp:88 (Mikko
  Koppanen).


0MQ version 2.1.9 (Stable), released on 2011/08/29
==================================================

Bug fixes
---------

* Fixed issue 240, assertion failure in pgm_socket.cpp:437.

* Fixed issue 238, assertion failure in zmq.cpp:655, when zmq_poll is
  used on an empty set, on Windows.

* Fixed issue 239, assertion failure in zmq.cpp:223, when ZMQ_SWAP was
  used with explicit identities and multiple SUB sockets.

* Fixed issue 236, zmq_send() and zmq_recv() did not always return
  error conditions such as EFSM properly. This bug was introduced in
  version 2.1.8 by the backport of changes for issue 231.

Building
--------

* 0MQ support for Android added (Bill Roberts, Mikko Koppanen).


0MQ version 2.1.8 (RC), released on 2011/07/28
==============================================

Bug fixes
---------

* Fixed issue 223, assertion failure in tcp_connecter.cpp:300 when
  connecting to a server that is on an unreachable network (errno is
  equal to ENETUNREACH).

* Fixed issue 228, assertion failure at rep.cpp:88 when HWM was reached.

* Fixed issue 231, assertion failure at mailbox.cpp:183 when too many
  pending socketpair operations were queued (major backport from 3.0).

* Fixed issue 234, assertion failure at mailbox.cpp:77 when Ctrl-C was
  used (only affected git master following backport for 231).

* Fixed issue 230, SIGPIPE killing servers when client disconnected, hit
  OS/X only.

Note: this release was renamed "release candidate" due to issue 236,
fixed in 2.1.9.


0MQ version 2.1.7 (Stable), released on 2011/05/12
==================================================

Bug fixes
---------

* Fixed issue 188, assert when closing socket that had unread multipart
  data still on it (affected PULL, SUB, ROUTER, and DEALER sockets).

* Fixed issue 191, message atomicity issue with PUB sockets (an old issue).

* Fixed issue 199 (affected ROUTER/XREP sockets, an old issue).

* Fixed issue 206, assertion failure in zmq.cpp:223, affected all sockets
  (bug was introduced in 2.1.6 as part of message validity checking).

* Fixed issue 211, REP socket asserted if sent malformed envelope (old issue
  due to abuse of assertions for error checking).

* Fixed issue 212, reconnect failing after resume from sleep on Windows
  (due to not handling WSAENETDOWN).

* Properly handle WSAENETUNREACH on Windows (e.g. if client connects
  before server binds).

* Fixed memory leak with threads on Windows.

Changes
-------

* Checks zmq_msg_t validity at each operation.

* Inproc performance tests now work on Windows.

* PGM wire format specification improved in zmq_pgm(7)

* Added thread latency/throughput performance examples.

* Added "--with-system-pgm" configure option to use already installed
  OpenPGM.

* Runtime checking of socket and context validity, to catch e.g. using a
  socket after closing it, or passing an invalid pointer to context/socket
  methods.

* Test cases moved off port 5555, which conflicts with other services.

* Clarified zmq_poll man page that the resolution of the timeout is 1msec.


0MQ version 2.1.6 (Broken), released on 2011/04/26
==================================================

Note that this version contained a malformed patch and is not usable.
It is not available for download, but is available in the git via the
2.1.6 tag.

0MQ version 2.1.5 (Broken), released on 2011/04/20
==================================================

Note that this version contained a malformed patch and is not usable.
It is not available for download, but is available in the git via the
2.1.5 tag.


0MQ version 2.1.4 (Stable), released on 2011/03/30
==================================================

Bug fixes
---------

* Fix to OpenPGM which was asserting on small messages (Steven McCoy).

Changes
-------

* Upgraded OpenPGM to version 5.1.115 (Pieter Hintjens).

* OpenPGM build changed to not install OpenPGM artifacts.


0MQ version 2.1.3 (Stable), released on 2011/03/21
==================================================

Bug fixes
---------

* Fix to PUSH sockets, which would sometimes deliver tail frames of a
  multipart message to new subscribers (Martin Sustrik).

* Fix to PUB sockets, which would sometimes deliver tail frames of a
  multipart message to new subscribers (Martin Sustrik).

* Windows build was broken due to EPROTONOSUPPORT not being defined. This
  has now been fixed (Martin Sustrik).

* Various fixes to make OpenVMS port work (Brett Cameron).

* Corrected Reference Manual to note that ZMQ_LINGER socket option may be
  set at any time, not just before connecting/binding (Pieter Hintjens).

* Fix to C++ binding to properly close sockets (Guido Goldstein).

* Removed obsolete assert from pgm_socket.cpp (Martin Sustrik).

Changes
-------

* Removed stand-alone devices (/devices subdirectory) from distribution.
  These undocumented programs remain available in older packages (Pieter
  Hintjens).

* OpenPGM default rate raised to 40mbps by default (Steven McCoy).

* ZMQ_DEALER and ZMQ_ROUTER macros provided to ease upgrade to 0MQ/3.0.
  These are scheduled to replace ZMQ_XREQ and ZMQ_XREP (Pieter Hintjens).

* Added man page for zmq_device(3) which was hereto undocumented (Pieter
  Hintjens).

* Removed zmq_queue(3), zmq_forwarder(3), zmq_streamer(3) man pages
  (Pieter Hintjens).

OpenPGM Integration
-------------------

* Upgraded OpenPGM to version 5.1.114 (Steven McCoy, Mikko Koppanen).

* Build system now calls OpenPGM build process directly, allowing easier
  future upgrades of OpenPGM (Mikko Koppanen).

* Build system allows configuration with arbitrary versions of OpenPGM
  (./configure --with-pgm=libpgm-x.y.z) (Mikko Koppanen).

* OpenPGM uses new PGM_ODATA_MAX_RTE controlling original data instead of
  PGM_TXW_MAX_RTE covering entire channel (Steven McCoy).

Building
--------

* 0MQ builds properly on FreeBSD (Mikko Koppanen).


0MQ version 2.1.2 (rc2), released on 2011/03/06
===============================================

Bug fixes
---------

* 0MQ now correctly handles durable inproc sockets; previously it ignored
  explicit identities on inproc sockets.

* Various memory leaks were fixed.

* OpenPGM sender/receiver creation fixed.


0MQ version 2.1.1 (rc1), released on 2011/02/23
===============================================

New functionality
-----------------

* New socket option ZMQ_RECONNECT_IVL_MAX added, allows for exponential
  back-off strategy when reconnecting.

* New socket option ZMQ_RECOVERY_IVL_MSEC added, as a fine-grained
  counterpart to ZMQ_RECOVERY_IVL (for multicast transports).

* If memory is exhausted, 0MQ warns with an explicit message before
  aborting the process.

* Size of inproc HWM and SWAP is sum of peers' HWMs and SWAPs (Douglas
  Greager, Martin Sustrik).

Bug fixes
---------

* 0MQ no longer asserts in mailbox.cpp when multiple peers connect with
  the same identity.

* 0MQ no longer asserts when rejecting an oversized message.

* 0MQ no longer asserts in pipe.cpp when the swap fills up.

* zmq_poll now works correctly with an empty poll set.

* Many more.

Building
--------

* 0MQ now builds correctly on CentOS, Debian 6, and SunOS/gcc3.

* Added WithOpenPGM configuration into MSVC builds.

Known issues
------------

* OpenPGM integration is still not fully stable.


0MQ version 2.1.0 (Beta), released on 2010/12/01
================================================

New functionality
-----------------

* New semantics for zmq_close () and zmq_term () ensure that all messages
  are sent before the application terminates. This behaviour may be
  modified using the new ZMQ_LINGER socket option; for further details
  refer to the reference manual.

* The new socket options ZMQ_FD and ZMQ_EVENTS provide a way to integrate
  0MQ sockets into existing poll/event loops.

* Sockets may now be migrated between OS threads, as long as the
  application ensures that a full memory barrier is issued.

* The 0MQ ABI exported by libzmq.so has been formalised; DSO symbol
  visibility is used on supported platforms to ensure that only public ABI
  symbols are exported. The library ABI version has been set to 1.0.0 for
  this release.

* OpenPGM has been updated to version 5.0.92. This version no longer
  depends on GLIB, and integration with 0MQ should be much improved.

* zmq_poll() now honors timeouts precisely, and no longer returns if no
  events are signaled.

* Blocking calls now return EINTR if interrupted by the delivery of a
  signal; this also means that language bindings which previously had
  problems with handling SIGINT/^C should now work correctly.

* The ZMQ_TYPE socket option was added; this allows retrieval of the socket
  type after creation.

* Added a ZMQ_VERSION macro to zmq.h for compile-time API version
  detection.

* The ZMQ_RECONNECT_IVL and ZMQ_BACKLOG socket options have been added.

Bug fixes
---------

* Forwarder and streamer devices now handle multi-part messages correctly.

* 0MQ no longer asserts when malformed data is received on the wire.

* 0MQ internal timers now work correctly if the TSC jumps backwards.

* The internal signalling functionality (mailbox) has been improved
  to automatically resize socket buffers on POSIX systems.

* Many more.

Building
--------

* 0MQ now builds correctly with many more non-GCC compilers (Sun Studio,
  Intel ICC, CLang).

* AIX and HP-UX builds should work now.

* FD_SETSIZE has been set to 1024 by default for MSVC builds.

* Windows builds using GCC (MinGW) now work out of the box.

Distribution
------------

* A simple framework for regression tests has been added, along with a few
  basic self-tests. The tests can be run using "make check".