Problem: 2 connects with same sourceip:port to different destip:port fail

Solution: during a connect with a TCP endpoint if a source address is
passed set the SO_REUSEADDR flag on the socket before the bind system
call.
Add unit test to cover this case for both IPv4 and IPv6.

src/tcp_connecter.cpp

@@ -314,6 +314,18 @@ int zmq::tcp_connecter_t::open ()
 
     // Set a source address for conversations
     if (tcp_addr->has_src_addr ()) {
+        //  Allow reusing of the address, to connect to different servers
+        //  using the same source port on the client.
+        int flag = 1;
+#ifdef ZMQ_HAVE_WINDOWS
+        rc = setsockopt (s, SOL_SOCKET, SO_REUSEADDR, (const char*) &flag,
+                sizeof (int));
+        wsa_assert (rc != SOCKET_ERROR);
+#else
+        rc = setsockopt (s, SOL_SOCKET, SO_REUSEADDR, &flag, sizeof (int));
+        errno_assert (rc == 0);
+#endif
+
         rc = ::bind (s, tcp_addr->src_addr (), tcp_addr->src_addrlen ());
         if (rc == -1)
             return -1;

tests/test_reqrep_tcp.cpp

@@ -131,6 +131,73 @@ void test_multi_connect_ipv4 (void)
     assert (rc == 0);
 }
 
+void test_multi_connect_ipv4_same_port (void)
+{
+    void *ctx = zmq_ctx_new ();
+    assert (ctx);
+
+    void *sb0 = zmq_socket (ctx, ZMQ_REP);
+    assert (sb0);
+    int rc = zmq_bind (sb0, "tcp://127.0.0.1:5560");
+    assert (rc == 0);
+
+    void *sb1 = zmq_socket (ctx, ZMQ_REP);
+    assert (sb1);
+    rc = zmq_bind (sb1, "tcp://127.0.0.1:5561");
+    assert (rc == 0);
+
+    void *sc0 = zmq_socket (ctx, ZMQ_REQ);
+    assert (sc0);
+    rc = zmq_connect (sc0, "tcp://127.0.0.1:5564;127.0.0.1:5560");
+    assert (rc == 0);
+    rc = zmq_connect (sc0, "tcp://127.0.0.1:5565;127.0.0.1:5561");
+    assert (rc == 0);
+
+    void *sc1 = zmq_socket (ctx, ZMQ_REQ);
+    assert (sc1);
+    rc = zmq_connect (sc1, "tcp://127.0.0.1:5565;127.0.0.1:5560");
+    assert (rc == 0);
+    rc = zmq_connect (sc1, "tcp://127.0.0.1:5564;127.0.0.1:5561");
+    assert (rc == 0);
+
+    bounce (sb0, sc0);
+    bounce (sb1, sc0);
+    bounce (sb0, sc1);
+    bounce (sb1, sc1);
+    bounce (sb0, sc0);
+    bounce (sb1, sc0);
+
+    rc = zmq_disconnect (sc1, "tcp://127.0.0.1:5565;127.0.0.1:5560");
+    assert (rc == 0);
+    rc = zmq_disconnect (sc1, "tcp://127.0.0.1:5564;127.0.0.1:5561");
+    assert (rc == 0);
+    rc = zmq_disconnect (sc0, "tcp://127.0.0.1:5564;127.0.0.1:5560");
+    assert (rc == 0);
+    rc = zmq_disconnect (sc0, "tcp://127.0.0.1:5565;127.0.0.1:5561");
+    assert (rc == 0);
+
+    rc = zmq_unbind (sb0, "tcp://127.0.0.1:5560");
+    assert (rc == 0);
+
+    rc = zmq_unbind (sb1, "tcp://127.0.0.1:5561");
+    assert (rc == 0);
+
+    rc = zmq_close (sc0);
+    assert (rc == 0);
+
+    rc = zmq_close (sc1);
+    assert (rc == 0);
+
+    rc = zmq_close (sb0);
+    assert (rc == 0);
+
+    rc = zmq_close (sb1);
+    assert (rc == 0);
+
+    rc = zmq_ctx_term (ctx);
+    assert (rc == 0);
+}
+
 void test_single_connect_ipv6 (void)
 {
     void *ctx = zmq_ctx_new ();
@@ -257,6 +324,87 @@ void test_multi_connect_ipv6 (void)
     assert (rc == 0);
 }
 
+void test_multi_connect_ipv6_same_port (void)
+{
+    void *ctx = zmq_ctx_new ();
+    assert (ctx);
+
+    if (!is_ipv6_available ()) {
+        zmq_ctx_term (ctx);
+        return;
+    }
+
+    void *sb0 = zmq_socket (ctx, ZMQ_REP);
+    assert (sb0);
+    int ipv6 = 1;
+    int rc = zmq_setsockopt (sb0, ZMQ_IPV6, &ipv6, sizeof (int));
+    assert (rc == 0);
+    rc = zmq_bind (sb0, "tcp://[::1]:5560");
+    assert (rc == 0);
+
+    void *sb1 = zmq_socket (ctx, ZMQ_REP);
+    assert (sb1);
+    rc = zmq_setsockopt (sb1, ZMQ_IPV6, &ipv6, sizeof (int));
+    assert (rc == 0);
+    rc = zmq_bind (sb1, "tcp://[::1]:5561");
+    assert (rc == 0);
+
+    void *sc0 = zmq_socket (ctx, ZMQ_REQ);
+    assert (sc0);
+    rc = zmq_setsockopt (sc0, ZMQ_IPV6, &ipv6, sizeof (int));
+    assert (rc == 0);
+    rc = zmq_connect (sc0, "tcp://[::1]:5564;[::1]:5560");
+    assert (rc == 0);
+    rc = zmq_connect (sc0, "tcp://[::1]:5565;[::1]:5561");
+    assert (rc == 0);
+
+    void *sc1 = zmq_socket (ctx, ZMQ_REQ);
+    assert (sc1);
+    rc = zmq_setsockopt (sc1, ZMQ_IPV6, &ipv6, sizeof (int));
+    assert (rc == 0);
+    rc = zmq_connect (sc1, "tcp://[::1]:5565;[::1]:5560");
+    assert (rc == 0);
+    rc = zmq_connect (sc1, "tcp://[::1]:5564;[::1]:5561");
+    assert (rc == 0);
+
+    bounce (sb0, sc0);
+    bounce (sb1, sc0);
+    bounce (sb0, sc1);
+    bounce (sb1, sc1);
+    bounce (sb0, sc0);
+    bounce (sb1, sc0);
+
+    rc = zmq_disconnect (sc1, "tcp://[::1]:5565;[::1]:5560");
+    assert (rc == 0);
+    rc = zmq_disconnect (sc1, "tcp://[::1]:5564;[::1]:5561");
+    assert (rc == 0);
+    rc = zmq_disconnect (sc0, "tcp://[::1]:5564;[::1]:5560");
+    assert (rc == 0);
+    rc = zmq_disconnect (sc0, "tcp://[::1]:5565;[::1]:5561");
+    assert (rc == 0);
+
+    rc = zmq_unbind (sb0, "tcp://[::1]:5560");
+    assert (rc == 0);
+
+    rc = zmq_unbind (sb1, "tcp://[::1]:5561");
+    assert (rc == 0);
+
+    rc = zmq_close (sc0);
+    assert (rc == 0);
+
+    rc = zmq_close (sc1);
+    assert (rc == 0);
+
+    rc = zmq_close (sb0);
+    assert (rc == 0);
+
+    rc = zmq_close (sb1);
+    assert (rc == 0);
+
+    rc = zmq_ctx_term (ctx);
+    assert (rc == 0);
+}
+
 int main (void)
 {
     setup_test_environment ();
@@ -265,9 +413,13 @@ int main (void)
 
     test_multi_connect_ipv4 ();
 
+    test_multi_connect_ipv4_same_port ();
+
     test_single_connect_ipv6 ();
 
     test_multi_connect_ipv6 ();
 
+    test_multi_connect_ipv6_same_port ();
+
     return 0 ;
 }