Account for control character as part of zmq_read_part (sonic-net#906)

Author: zbud-msft

common/events_common.h

@@ -310,16 +310,23 @@ struct serialization
         more = 0;
         zmq_msg_init(&msg);
         int rc = zmq_msg_recv(&msg, sock, flag);
-        if (rc != -1) {
+        if (rc == 1) {
+            char control_character = *(char*)zmq_msg_data(&msg);
+            if (control_character == 0x01 || control_character == 0x00) {
+                SWSS_LOG_INFO("Received subscription/unsubscription message when XSUB connect to XPUB: %c", control_character);
+            } else {
+                SWSS_LOG_DEBUG("Received non subscription based control character: %c", control_character);
+            }
+            rc = 0;
+        } else if (rc != -1) {
             size_t more_size = sizeof (more);
 
             zmq_getsockopt (sock, ZMQ_RCVMORE, &more, &more_size);
 
             rc = zmsg_to_map(msg, data);
             RET_ON_ERR(rc == 0, "Failed to deserialize part rc=%d", rc);
             /* read more flag if message read fails to de-serialize */
-        }
-        else {
+        } else {
             /* override with zmq err */
             rc = zmq_errno();
             if (rc != 11) {
@@ -332,7 +339,7 @@ struct serialization
         return rc;
     }
 
-       
+
     template<typename DT>
     int
     zmq_send_part(void *sock, int flag, const DT &data)

tests/events_common_ut.cpp

@@ -97,9 +97,51 @@ TEST(events_common, send_recv)
     zmq_ctx_term(zmq_ctx);
 }
 
+TEST(events_common, send_recv_control_character)
+{
+#if 0
+    {
+        /* Direct log messages to stdout */
+        string dummy, op("STDOUT");
+        swss::Logger::swssOutputNotify(dummy, op);
+        swss::Logger::setMinPrio(swss::Logger::SWSS_DEBUG);
+    }
+#endif
 
+    char *path = "tcp://127.0.0.1:5570";
+    void *zmq_ctx = zmq_ctx_new();
+    void *sock_p0 = zmq_socket (zmq_ctx, ZMQ_PAIR);
+    EXPECT_EQ(0, zmq_connect (sock_p0, path));
 
+    void *sock_p1 = zmq_socket (zmq_ctx, ZMQ_PAIR);
+    EXPECT_EQ(0, zmq_bind (sock_p1, path));
 
+    string source;
+    map<string, string> m;
+
+    // Subscription based control character test
+    zmq_msg_t sub_msg;
+    zmq_msg_init_size(&sub_msg, 1);
+    *(char*)zmq_msg_data(&sub_msg) = 0x01;
+    EXPECT_EQ(1, zmq_msg_send(&sub_msg, sock_p0, 0));
+    zmq_msg_close(&sub_msg);
+    // First part will be read only and will return as 0, but will not be deserialized event
+    EXPECT_EQ(0, zmq_message_read(sock_p1, 0, source, m));
+    EXPECT_EQ("", source);
+    EXPECT_EQ(0, m.size());
+
+   // Non-subscription based control character test
+    zmq_msg_t ctrl_msg;
+    zmq_msg_init_size(&ctrl_msg, 1);
+    *(char*)zmq_msg_data(&ctrl_msg) = 0x07;
+    EXPECT_EQ(1, zmq_msg_send(&ctrl_msg, sock_p0, 0));
+    zmq_msg_close(&ctrl_msg);
+    // First part will be read only and will return as 0, but will not be deserialized event
+    EXPECT_EQ(0, zmq_message_read(sock_p1, 0, source, m));
+    EXPECT_EQ("", source);
+    EXPECT_EQ(0, m.size());
 
-
-
+    zmq_close(sock_p0);
+    zmq_close(sock_p1);
+    zmq_ctx_term(zmq_ctx);
+}