problem: zeromq doesn't has a thread-safe peer to peer socket

Solution: a new socket type, called PEER. Very similar to SERVER, but can only connect to other PEERs. Also a new zmq_connect_peer method, that connect and return a routing-id in thread-safe and atomic operation

.gitignore

@@ -156,12 +156,14 @@ test_ws_transport
 test_wss_transport
 test_socks
 test_xpub_manual_last_value
+test_peer
 unittest_ip_resolver
 unittest_mtrie
 unittest_poller
 unittest_radix_tree
 unittest_udp_address
 unittest_ypipe
+unittests/unittest_curve_encoding
 tests/test*.log
 tests/test*.trs
 unittests/unittest*.log
@@ -205,4 +207,4 @@ core
 build
 test-suite.log
 .idea/
-cmake-build-debug/
\ No newline at end of file
+cmake-build-debug/

CMakeLists.txt

@@ -822,6 +822,7 @@ set(cxx-sources
   own.cpp
   null_mechanism.cpp
   pair.cpp
+  peer.cpp
   pgm_receiver.cpp
   pgm_sender.cpp
   pgm_socket.cpp
@@ -947,6 +948,7 @@ set(cxx-sources
   options.hpp
   own.hpp
   pair.hpp
+  peer.hpp
   pgm_receiver.hpp
   pgm_sender.hpp
   pgm_socket.hpp

Makefile.am

@@ -126,6 +126,8 @@ src_libzmq_la_SOURCES = \
 	src/own.hpp \
 	src/pair.cpp \
 	src/pair.hpp \
+	src/peer.cpp \
+	src/peer.hpp \
 	src/pgm_receiver.cpp \
 	src/pgm_receiver.hpp \
 	src/pgm_sender.cpp \
@@ -1034,7 +1036,8 @@ test_apps += tests/test_poller \
 	tests/test_dgram \
 	tests/test_app_meta \
 	tests/test_xpub_manual_last_value \
-	tests/test_router_notify
+	tests/test_router_notify \
+	tests/test_peer
 
 tests_test_poller_SOURCES = tests/test_poller.cpp
 tests_test_poller_LDADD = ${TESTUTIL_LIBS} src/libzmq.la
@@ -1075,6 +1078,10 @@ tests_test_app_meta_CPPFLAGS = ${TESTUTIL_CPPFLAGS}
 tests_test_router_notify_SOURCES = tests/test_router_notify.cpp
 tests_test_router_notify_LDADD = ${TESTUTIL_LIBS} src/libzmq.la
 tests_test_router_notify_CPPFLAGS = ${TESTUTIL_CPPFLAGS}
+
+tests_test_peer_SOURCES = tests/test_peer.cpp
+tests_test_peer_LDADD = ${TESTUTIL_LIBS} src/libzmq.la
+tests_test_peer_CPPFLAGS = ${TESTUTIL_CPPFLAGS}
 endif
 
 if ENABLE_STATIC

doc/Makefile.am

 #
 # documentation
 #
-MAN3 = zmq_bind.3 zmq_unbind.3 zmq_connect.3 zmq_disconnect.3 zmq_close.3 \
+MAN3 = zmq_bind.3 zmq_unbind.3 zmq_connect.3 zmq_connect_peer.3 zmq_disconnect.3 zmq_close.3 \
     zmq_ctx_new.3 zmq_ctx_term.3 zmq_ctx_get.3 zmq_ctx_set.3 zmq_ctx_shutdown.3 \
     zmq_msg_init.3 zmq_msg_init_data.3 zmq_msg_init_size.3 \
     zmq_msg_move.3 zmq_msg_copy.3 zmq_msg_size.3 zmq_msg_data.3 zmq_msg_close.3 \

doc/zmq_connect_peer.txt

+zmq_connect_peer(3)
+===================
+
+
+NAME
+----
+zmq_connect_peer - create outgoing connection from socket and return the connection routing id in thread-safe and atomic way.
+
+
+SYNOPSIS
+--------
+*uint32_t zmq_connect_peer (void '*socket', const char '*endpoint');*
+
+
+DESCRIPTION
+-----------
+The _zmq_connect_peer()_ function connects a 'ZMQ_PEER' socket to an 'endpoint' and then returns the endpoint 'routing_id'.
+
+The 'endpoint' is a string consisting of a 'transport'`://` followed by an
+'address'. The 'transport' specifies the underlying protocol to use. The
+'address' specifies the transport-specific address to connect to.
+
+The function is supported only on the 'ZMQ_PEER' socket type and would return `0` with 'errno' set to 'ENOTSUP' otherwise.
+
+The _zmq_connect_peer()_ support the following transports:
+
+'tcp':: unicast transport using TCP, see linkzmq:zmq_tcp[7]
+'ipc':: local inter-process communication transport, see linkzmq:zmq_ipc[7]
+'inproc':: local in-process (inter-thread) communication transport, see linkzmq:zmq_inproc[7]
+'ws':: unicast transport using WebSockets, see linkzmq:zmq_ws[7]
+'wss':: unicast transport using WebSockets over TLS, see linkzmq:zmq_wss[7]
+
+RETURN VALUE
+------------
+The _zmq_connect_peer()_ function returns the peer 'routing_id' if successful. Otherwise it returns
+`0` and sets 'errno' to one of the values defined below.
+
+
+ERRORS
+------
+*EINVAL*::
+The endpoint supplied is invalid.
+*EPROTONOSUPPORT*::
+The requested 'transport' protocol is not supported with 'ZMQ_PEER'.
+*ENOCOMPATPROTO*::
+The requested 'transport' protocol is not compatible with the socket type.
+*ETERM*::
+The 0MQ 'context' associated with the specified 'socket' was terminated.
+*ENOTSOCK*::
+The provided 'socket' was invalid.
+*EMTHREAD*::
+No I/O thread is available to accomplish the task.
+*ENOTSUP*::
+The socket is not of type 'ZMQ_PEER'.
+*EFAULT*::
+The 'ZMQ_IMMEDIATE' option is set on the socket.
+
+EXAMPLE
+-------
+.Connecting a peer socket to a TCP transport and sending a message
+----
+/* Create a ZMQ_SUB socket */
+void *socket = zmq_socket (context, ZMQ_PEER);
+assert (socket);
+/* Connect it to the host server001, port 5555 using a TCP transport */
+uint32_t routing_id = zmq_connect (socket, "tcp://server001:5555");
+assert (routing_id == 0);
+/* Sending a message to the peer  */
+zmq_msg_t msg;
+int rc = zmq_msg_init_data (&msg, "HELLO", 5, NULL, NULL);
+assert (rc == 0);
+rc = zmq_msg_set_routing_id (&msg, routing_id);
+assert (rc == 0);
+rc = zmq_msg_send (&msg, socket, 0);
+assert (rc == 5);
+rc = zmq_msg_close (&msg);
+assert (rc == 0);
+----
+
+
+SEE ALSO
+--------
+linkzmq:zmq_connect[3]
+linkzmq:zmq_bind[3]
+linkzmq:zmq_socket[3]
+linkzmq:zmq[7]
+
+
+AUTHORS
+-------
+This page was written by the 0MQ community. To make a change please
+read the 0MQ Contribution Policy at <http://www.zeromq.org/docs:contributing>.

doc/zmq_socket.txt

@@ -59,6 +59,7 @@ Following are the thread safe sockets:
 * ZMQ_RADIO
 * ZMQ_SCATTER
 * ZMQ_GATHER
+* ZMQ_PEER
 
 .Socket types
 The following sections present the socket types defined by 0MQ, grouped by the
@@ -434,6 +435,48 @@ Outgoing routing strategy:: N/A
 Action in mute state:: Block
 
 
+Peer-to-peer pattern
+~~~~~~~~~~~~~~~~~~~~~~
+
+The peer-to-peer pattern is used to connect a peer to multiple peers.
+Peer can both connect and bind and mix both of them with the same socket.
+The peer-to-peer pattern is useful to build peer-to-peer networks (e.g zyre, bitcoin, torrent)
+where a peer can both accept connections from other peers or connect to them.
+
+NOTE: Peer-to-peer is still in draft phase.
+
+ZMQ_PEER
+^^^^^^^^
+A 'ZMQ_PEER' socket talks to a set of 'ZMQ_PEER' sockets.
+
+To connect and fetch the 'routing_id' of the peer use linkzmq:zmq_connect_peer[3].
+
+Each received message has a 'routing_id' that is a 32-bit unsigned integer.
+The application can fetch this with linkzmq:zmq_msg_routing_id[3].
+
+To send a message to a given 'ZMQ_PEER' peer the application must set the peer's
+'routing_id' on the message, using linkzmq:zmq_msg_set_routing_id[3].
+
+If the 'routing_id' is not specified, or does not refer to a connected client
+peer, the send call will fail with EHOSTUNREACH. If the outgoing buffer for
+the peer is full, the send call shall block, unless ZMQ_DONTWAIT is
+used in the send, in which case it shall fail with EAGAIN. The 'ZMQ_PEER'
+socket shall not drop messages in any case.
+
+NOTE: 'ZMQ_PEER' sockets are threadsafe. They do not accept the ZMQ_SNDMORE
+option on sends not ZMQ_RCVMORE on receives. This limits them to single part
+data.
+
+[horizontal]
+.Summary of ZMQ_PEER characteristics
+Compatible peer sockets:: 'ZMQ_PEER'
+Direction:: Bidirectional
+Send/receive pattern:: Unrestricted
+Outgoing routing strategy:: See text
+Incoming routing strategy:: Fair-queued
+Action in mute state:: Return EAGAIN
+
+
 Native Pattern
 ~~~~~~~~~~~~~~
 The native pattern is used for communicating with TCP peers and allows

include/zmq.h

@@ -263,7 +263,7 @@ typedef struct zmq_msg_t
 #endif
 } zmq_msg_t;
 
-typedef void(zmq_free_fn) (void *data_, void *hint_);
+typedef void (zmq_free_fn) (void *data_, void *hint_);
 
 ZMQ_EXPORT int zmq_msg_init (zmq_msg_t *msg_);
 ZMQ_EXPORT int zmq_msg_init_size (zmq_msg_t *msg_, size_t size_);
@@ -597,7 +597,7 @@ ZMQ_EXPORT void zmq_atomic_counter_destroy (void **counter_p_);
 
 #define ZMQ_HAVE_TIMERS
 
-typedef void(zmq_timer_fn) (int timer_id, void *arg);
+typedef void (zmq_timer_fn) (int timer_id, void *arg);
 
 ZMQ_EXPORT void *zmq_timers_new (void);
 ZMQ_EXPORT int zmq_timers_destroy (void **timers_p);
@@ -634,7 +634,7 @@ ZMQ_EXPORT unsigned long zmq_stopwatch_stop (void *watch_);
 /*  Sleeps for specified number of seconds.                                   */
 ZMQ_EXPORT void zmq_sleep (int seconds_);
 
-typedef void(zmq_thread_fn) (void *);
+typedef void (zmq_thread_fn) (void *);
 
 /* Start a thread. Returns a handle to the thread.                            */
 ZMQ_EXPORT void *zmq_threadstart (zmq_thread_fn *func_, void *arg_);
@@ -658,6 +658,7 @@ ZMQ_EXPORT void zmq_threadclose (void *thread_);
 #define ZMQ_GATHER 16
 #define ZMQ_SCATTER 17
 #define ZMQ_DGRAM 18
+#define ZMQ_PEER 19
 
 /*  DRAFT Socket options.                                                     */
 #define ZMQ_ZAP_ENFORCE_DOMAIN 93
@@ -694,6 +695,7 @@ ZMQ_EXPORT int zmq_ctx_get_ext (void *context_,
 /*  DRAFT Socket methods.                                                     */
 ZMQ_EXPORT int zmq_join (void *s, const char *group);
 ZMQ_EXPORT int zmq_leave (void *s, const char *group);
+ZMQ_EXPORT uint32_t zmq_connect_peer (void *s_, const char *addr_);
 
 /*  DRAFT Msg methods.                                                        */
 ZMQ_EXPORT int zmq_msg_set_routing_id (zmq_msg_t *msg, uint32_t routing_id);

src/mechanism.cpp

@@ -93,6 +93,7 @@ const char socket_type_dish[] = "DISH";
 const char socket_type_gather[] = "GATHER";
 const char socket_type_scatter[] = "SCATTER";
 const char socket_type_dgram[] = "DGRAM";
+const char socket_type_peer[] = "PEER";
 #endif
 
 const char *zmq::mechanism_t::socket_type_string (int socket_type_)
@@ -106,7 +107,7 @@ const char *zmq::mechanism_t::socket_type_string (int socket_type_)
 #ifdef ZMQ_BUILD_DRAFT_API
       socket_type_server, socket_type_client, socket_type_radio,
       socket_type_dish,   socket_type_gather, socket_type_scatter,
-      socket_type_dgram
+      socket_type_dgram,  socket_type_peer
 #endif
     };
     static const size_t names_count = sizeof (names) / sizeof (names[0]);
@@ -353,6 +354,8 @@ bool zmq::mechanism_t::check_socket_type (const char *type_,
             return strequals (type_, len_, socket_type_gather);
         case ZMQ_DGRAM:
             return strequals (type_, len_, socket_type_dgram);
+        case ZMQ_PEER:
+            return strequals (type_, len_, socket_type_peer);
 #endif
         default:
             break;

src/peer.cpp

+/*
+    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+
+    This file is part of libzmq, the ZeroMQ core engine in C++.
+
+    libzmq is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License (LGPL) as published
+    by the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    As a special exception, the Contributors give you permission to link
+    this library with independent modules to produce an executable,
+    regardless of the license terms of these independent modules, and to
+    copy and distribute the resulting executable under terms of your choice,
+    provided that you also meet, for each linked independent module, the
+    terms and conditions of the license of that module. An independent
+    module is a module which is not derived from or based on this library.
+    If you modify this library, you must extend this exception to your
+    version of the library.
+
+    libzmq is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "precompiled.hpp"
+#include "macros.hpp"
+#include "peer.hpp"
+#include "pipe.hpp"
+#include "wire.hpp"
+#include "random.hpp"
+#include "likely.hpp"
+#include "err.hpp"
+
+zmq::peer_t::peer_t (class ctx_t *parent_, uint32_t tid_, int sid_) :
+    server_t (parent_, tid_, sid_)
+{
+    options.type = ZMQ_PEER;
+}
+
+uint32_t zmq::peer_t::connect_peer (const char *endpoint_uri_)
+{
+    scoped_optional_lock_t sync_lock (&_sync);
+
+    // connect_peer cannot work with immediate enabled
+    if (options.immediate == 1) {
+        errno = EFAULT;
+        return 0;
+    }
+
+    int rc = socket_base_t::connect_internal (endpoint_uri_);
+    if (rc != 0)
+        return 0;
+
+    return _peer_last_routing_id;
+}
+
+void zmq::peer_t::xattach_pipe (pipe_t *pipe_,
+                                bool subscribe_to_all_,
+                                bool locally_initiated_)
+{
+    server_t::xattach_pipe (pipe_, subscribe_to_all_, locally_initiated_);
+    _peer_last_routing_id = pipe_->get_server_socket_routing_id ();
+}

src/peer.hpp

+/*
+    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+
+    This file is part of libzmq, the ZeroMQ core engine in C++.
+
+    libzmq is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License (LGPL) as published
+    by the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    As a special exception, the Contributors give you permission to link
+    this library with independent modules to produce an executable,
+    regardless of the license terms of these independent modules, and to
+    copy and distribute the resulting executable under terms of your choice,
+    provided that you also meet, for each linked independent module, the
+    terms and conditions of the license of that module. An independent
+    module is a module which is not derived from or based on this library.
+    If you modify this library, you must extend this exception to your
+    version of the library.
+
+    libzmq is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef __ZMQ_PEER_HPP_INCLUDED__
+#define __ZMQ_PEER_HPP_INCLUDED__
+
+#include <map>
+
+#include "socket_base.hpp"
+#include "server.hpp"
+#include "session_base.hpp"
+#include "stdint.hpp"
+#include "blob.hpp"
+#include "fq.hpp"
+
+namespace zmq
+{
+class ctx_t;
+class msg_t;
+class pipe_t;
+
+class peer_t ZMQ_FINAL : public server_t
+{
+  public:
+    peer_t (zmq::ctx_t *parent_, uint32_t tid_, int sid_);
+
+    //  Overrides of functions from socket_base_t.
+    void xattach_pipe (zmq::pipe_t *pipe_,
+                       bool subscribe_to_all_,
+                       bool locally_initiated_);
+
+    uint32_t connect_peer (const char *endpoint_uri_);
+
+  private:
+    uint32_t _peer_last_routing_id;
+
+    ZMQ_NON_COPYABLE_NOR_MOVABLE (peer_t)
+};
+}
+
+#endif

src/server.hpp

@@ -45,7 +45,7 @@ class msg_t;
 class pipe_t;
 
 //  TODO: This class uses O(n) scheduling. Rewrite it to use O(1) algorithm.
-class server_t ZMQ_FINAL : public socket_base_t
+class server_t : public socket_base_t
 {
   public:
     server_t (zmq::ctx_t *parent_, uint32_t tid_, int sid_);

src/session_base.cpp

@@ -87,6 +87,7 @@ zmq::session_base_t *zmq::session_base_t::create (class io_thread_t *io_thread_,
         case ZMQ_GATHER:
         case ZMQ_SCATTER:
         case ZMQ_DGRAM:
+        case ZMQ_PEER:
             s = new (std::nothrow)
               session_base_t (io_thread_, active_, socket_, options_, addr_);
             break;

src/socket_base.cpp

@@ -100,6 +100,7 @@
 #include "gather.hpp"
 #include "scatter.hpp"
 #include "dgram.hpp"
+#include "peer.hpp"
 
 void zmq::socket_base_t::inprocs_t::emplace (const char *endpoint_uri_,
                                              pipe_t *pipe_)
@@ -207,6 +208,9 @@ zmq::socket_base_t *zmq::socket_base_t::create (int type_,
         case ZMQ_DGRAM:
             s = new (std::nothrow) dgram_t (parent_, tid_, sid_);
             break;
+        case ZMQ_PEER:
+            s = new (std::nothrow) peer_t (parent_, tid_, sid_);
+            break;
         default:
             errno = EINVAL;
             return NULL;
@@ -228,6 +232,7 @@ zmq::socket_base_t::socket_base_t (ctx_t *parent_,
                                    int sid_,
                                    bool thread_safe_) :
     own_t (parent_, tid_),
+    _sync (),
     _tag (0xbaddecaf),
     _ctx_terminated (false),
     _destroyed (false),
@@ -240,7 +245,6 @@ zmq::socket_base_t::socket_base_t (ctx_t *parent_,
     _monitor_events (0),
     _thread_safe (thread_safe_),
     _reaper_signaler (NULL),
-    _sync (),
     _monitor_sync ()
 {
     options.socket_id = sid_;
@@ -740,7 +744,11 @@ int zmq::socket_base_t::bind (const char *endpoint_uri_)
 int zmq::socket_base_t::connect (const char *endpoint_uri_)
 {
     scoped_optional_lock_t sync_lock (_thread_safe ? &_sync : NULL);
+    return connect_internal (endpoint_uri_);
+}
 
+int zmq::socket_base_t::connect_internal (const char *endpoint_uri_)
+{
     if (unlikely (_ctx_terminated)) {
         errno = ETERM;
         return -1;

src/socket_base.hpp

@@ -205,6 +205,11 @@ class socket_base_t : public own_t,
     //  Delay actual destruction of the socket.
     void process_destroy () ZMQ_FINAL;
 
+    int connect_internal (const char *endpoint_uri_);
+
+    // Mutex for synchronize access to the socket in thread safe mode
+    mutex_t _sync;
+
   private:
     // test if event should be sent and then dispatch it
     void event (const endpoint_uri_pair_t &endpoint_uri_pair_,
@@ -336,9 +341,6 @@ class socket_base_t : public own_t,
     // Signaler to be used in the reaping stage
     signaler_t *_reaper_signaler;
 
-    // Mutex for synchronize access to the socket in thread safe mode
-    mutex_t _sync;
-
     // Mutex to synchronize access to the monitor Pair socket
     mutex_t _monitor_sync;
 

src/zmq.cpp

@@ -40,6 +40,7 @@
 
 #include "macros.hpp"
 #include "poller.hpp"
+#include "peer.hpp"
 
 #if !defined ZMQ_HAVE_POLLER
 //  On AIX platform, poll.h has to be included first to get consistent
@@ -336,6 +337,28 @@ int zmq_connect (void *s_, const char *addr_)
     return s->connect (addr_);
 }
 
+uint32_t zmq_connect_peer (void *s_, const char *addr_)
+{
+    zmq::peer_t *s = static_cast<zmq::peer_t *> (s_);
+    if (!s_ || !s->check_tag ()) {
+        errno = ENOTSOCK;
+        return 0;
+    }
+
+    int socket_type;
+    size_t socket_type_size = sizeof (socket_type);
+    if (s->getsockopt (ZMQ_TYPE, &socket_type, &socket_type_size) != 0)
+        return 0;
+
+    if (socket_type != ZMQ_PEER) {
+        errno = ENOTSUP;
+        return 0;
+    }
+
+    return s->connect_peer (addr_);
+}
+
+
 int zmq_unbind (void *s_, const char *addr_)
 {
     zmq::socket_base_t *s = as_socket_base_t (s_);

src/zmq_draft.h

@@ -45,6 +45,7 @@
 #define ZMQ_GATHER 16
 #define ZMQ_SCATTER 17
 #define ZMQ_DGRAM 18
+#define ZMQ_PEER 19
 
 /*  DRAFT Socket options.                                                     */
 #define ZMQ_ZAP_ENFORCE_DOMAIN 93

tests/CMakeLists.txt

@@ -162,6 +162,7 @@ if(ENABLE_DRAFTS)
     test_app_meta
     test_router_notify
     test_xpub_manual_last_value
+    test_peer
   )
 endif()
 

tests/test_peer.cpp

+/*
+    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+
+    This file is part of libzmq, the ZeroMQ core engine in C++.
+
+    libzmq is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License (LGPL) as published
+    by the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    As a special exception, the Contributors give you permission to link
+    this library with independent modules to produce an executable,
+    regardless of the license terms of these independent modules, and to
+    copy and distribute the resulting executable under terms of your choice,
+    provided that you also meet, for each linked independent module, the
+    terms and conditions of the license of that module. An independent
+    module is a module which is not derived from or based on this library.
+    If you modify this library, you must extend this exception to your
+    version of the library.
+
+    libzmq is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "testutil.hpp"
+#include "testutil_unity.hpp"
+
+SETUP_TEARDOWN_TESTCONTEXT
+
+void test_peer ()
+{
+    size_t len = MAX_SOCKET_STRING;
+    char my_endpoint[MAX_SOCKET_STRING];
+
+    void *peer1 = test_context_socket (ZMQ_PEER);
+    bind_loopback (peer1, false, my_endpoint, len);
+
+    void *peer2 = test_context_socket (ZMQ_PEER);
+    uint32_t peer1_routing_id = zmq_connect_peer (peer2, my_endpoint);
+    TEST_ASSERT_NOT_EQUAL (0, peer1_routing_id);
+
+    {
+        zmq_msg_t msg;
+        TEST_ASSERT_SUCCESS_ERRNO (zmq_msg_init_size (&msg, 1));
+
+        char *data = static_cast<char *> (zmq_msg_data (&msg));
+        data[0] = 1;
+
+        TEST_ASSERT_SUCCESS_ERRNO (
+          zmq_msg_set_routing_id (&msg, peer1_routing_id));
+
+        int rc = zmq_msg_send (&msg, peer2, 0);
+        TEST_ASSERT_EQUAL_INT (1, rc);
+    }
+
+    uint32_t peer2_routing_id;
+    {
+        zmq_msg_t msg;
+        TEST_ASSERT_SUCCESS_ERRNO (zmq_msg_init (&msg));
+
+        int rc = TEST_ASSERT_SUCCESS_ERRNO (zmq_msg_recv (&msg, peer1, 0));
+        TEST_ASSERT_EQUAL_INT (1, rc);
+
+        peer2_routing_id = zmq_msg_routing_id (&msg);
+        TEST_ASSERT_NOT_EQUAL (0, peer2_routing_id);
+
+        TEST_ASSERT_SUCCESS_ERRNO (zmq_msg_close (&msg));
+    }
+
+    {
+        zmq_msg_t msg;
+        TEST_ASSERT_SUCCESS_ERRNO (zmq_msg_init_size (&msg, 1));
+
+        char *data = static_cast<char *> (zmq_msg_data (&msg));
+        data[0] = 2;
+
+        TEST_ASSERT_SUCCESS_ERRNO (
+          zmq_msg_set_routing_id (&msg, peer2_routing_id));
+
+        int rc = zmq_msg_send (&msg, peer1, 0);
+        TEST_ASSERT_EQUAL_INT (1, rc);
+    }
+
+    {
+        zmq_msg_t msg;
+        TEST_ASSERT_SUCCESS_ERRNO (zmq_msg_init (&msg));
+
+        int rc = zmq_msg_recv (&msg, peer2, 0);
+        TEST_ASSERT_EQUAL_INT (1, rc);
+
+        uint32_t routing_id = zmq_msg_routing_id (&msg);
+        TEST_ASSERT_EQUAL_UINT32 (peer1_routing_id, routing_id);
+
+        TEST_ASSERT_SUCCESS_ERRNO (zmq_msg_close (&msg));
+    }
+
+    test_context_socket_close (peer1);
+    test_context_socket_close (peer2);
+}
+
+int main (void)
+{
+    setup_test_environment ();
+
+    UNITY_BEGIN ();
+    RUN_TEST (test_peer);
+    return UNITY_END ();
+}