MXS-1555: Fix persistent pool qualification

When packets were routed individually, the qualification for the
persistent pool was done before the current command was updated. In
addition to this, the previous commit doesn't seem like it can even build.

server/modules/protocol/MySQL/MySQLClient/mysql_client.c

@@ -957,6 +957,30 @@ gw_read_normal_data(DCB *dcb, GWBUF *read_buffer, int nbytes_read)
     return gw_read_finish_processing(dcb, read_buffer, capabilities);
 }
 
+/**
+ * Check if a connection qualifies to be added into the persistent connection pool
+ *
+ * @param dcb The client DCB to check
+ */
+void check_pool_candidate(DCB* dcb)
+{
+    MXS_SESSION *session = dcb->session;
+    MySQLProtocol *proto = (MySQLProtocol*)dcb->protocol;
+
+    if (proto->current_command == MYSQL_COM_QUIT)
+    {
+        /** The client is closing the connection. We know that this will be the
+         * last command the client sends so the backend connections are very likely
+         * to be in an idle state.
+         *
+         * If the client is pipelining the queries (i.e. sending N request as
+         * a batch and then expecting N responses) then it is possible that
+         * the backend connections are not idle when the COM_QUIT is received.
+         * In most cases we can assume that the connections are idle. */
+        session_qualify_for_pool(session);
+    }
+}
+
 /**
  * @brief Client read event, common processing after single statement handling
  *
@@ -977,25 +1001,10 @@ gw_read_finish_processing(DCB *dcb, GWBUF *read_buffer, uint64_t capabilities)
     /** Reset error handler when routing of the new query begins */
     dcb->dcb_errhandle_called = false;
 
-    if (proto->current_command == MYSQL_COM_QUIT)
-    {
-        /** The client is closing the connection. We know that this will be the
-         * last command the client sends so the backend connections are very likely
-         * to be in an idle state.
-         *
-         * If the client is pipelining the queries (i.e. sending N request as
-         * a batch and then expecting N responses) then it is possible that
-         * the backend connections are not idle when the COM_QUIT is received.
-         * In most cases we can assume that the connections are idle. */
-        session_qualify_for_pool(session);
-    }
-
     if (rcap_type_required(capabilities, RCAP_TYPE_STMT_INPUT))
     {
         /**
-         * Feed each statement completely and separately
+         * Feed each statement completely and separately to router.
-         * to router. The routing functions return 1 for
-         * success or 0 for failure.
          */
         return_code = route_by_statement(session, capabilities, &read_buffer) ? 0 : 1;
 
@@ -1010,9 +1019,10 @@ gw_read_finish_processing(DCB *dcb, GWBUF *read_buffer, uint64_t capabilities)
     }
     else if (NULL != session->router_session || (rcap_type_required(capabilities, RCAP_TYPE_NO_RSESSION)))
     {
-        /** Feed whole packet to router, which will free it
+        /** Check if this connection qualifies for the connection pool */
-         *  and return 1 for success, 0 for failure
+        check_pool_candidate(dcb);
-         */
+
+        /** Feed the whole buffer to the router */
         return_code = MXS_SESSION_ROUTE_QUERY(session, read_buffer) ? 0 : 1;
     }
     /* else return_code is still 0 from when it was originally set */
@@ -1437,6 +1447,30 @@ retblock:
     return 1;
 }
 
+/**
+ * Update protocol tracking information for an individual statement
+ *
+ * @param dcb    Client DCB
+ * @param buffer Buffer containing a single packet
+ */
+void update_current_command(DCB* dcb, GWBUF* buffer)
+{
+    MySQLProtocol *proto = (MySQLProtocol*)dcb->protocol;
+    uint8_t cmd = (uint8_t)MYSQL_COM_QUERY;
+
+    /**
+     * As we are routing individual packets, we can extract the command byte here.
+     * Empty packets are treated as COM_QUERY packets by default.
+     */
+    gwbuf_copy_data(buffer, MYSQL_HEADER_LEN, 1, &cmd);
+    proto->current_command = cmd;
+
+    /**
+     * Now that we have the current command, we can check if this connection
+     * can be a candidate for the connection pool.
+     */
+    check_pool_candidate(dcb);
+}
 
 /**
  * Detect if buffer includes partial mysql packet or multiple packets.
@@ -1496,12 +1530,10 @@ static int route_by_statement(MXS_SESSION* session, uint64_t capabilities, GWBUF
              */
             gwbuf_set_type(packetbuf, GWBUF_TYPE_SINGLE_STMT);
 
-            /** As we are routing packets, we can extract the command byte here.
+            /**
-             * Empty packets are treated as COM_QUERY packets by default. */
+             * Update the currently command being executed.
-            uint8_t cmd = (uint8_t)MYSQL_COM_QUERY;
+             */
-            gwbuf_copy_data(packetbuf, MYSQL_HEADER_LEN, 1, &cmd);
+            update_current_command(session->client_dcb, packetbuf);
-            MySQLProtocol *proto = (MySQLProtocol*)dcb->protocol;
-            proto->current_command = cmd;
 
             if (rcap_type_required(capabilities, RCAP_TYPE_CONTIGUOUS_INPUT))
             {