MXS-1625 Add QueryClassifier class

This is the first step in providing a QueryClassifier class
that is capable of performing context dependent query classification,
where the context is essentially the session state.

include/maxscale/queryclassifier.hh

@@ -0,0 +1,51 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <maxscale/cppdefs.hh>
+#include <maxscale/router.h>
+#include <maxscale/session.h>
+
+namespace maxscale
+{
+
+class QueryClassifier
+{
+    QueryClassifier(const QueryClassifier&) = delete;
+    QueryClassifier& operator = (const QueryClassifier&) = delete;
+
+public:
+    // NOTE: For the time being these must be exactly like the ones in readwritesplit.hh
+    enum
+    {
+        TARGET_UNDEFINED = 0x00,
+        TARGET_MASTER    = 0x01,
+        TARGET_SLAVE     = 0x02,
+        TARGET_ALL       = 0x08
+    };
+
+    QueryClassifier(MXS_SESSION* pSession,
+                    mxs_target_t use_sql_variables_in);
+
+    void set_load_active(bool active);
+    bool load_active() const;
+
+    uint32_t get_route_target(uint8_t command, uint32_t qtype);
+
+private:
+    MXS_SESSION* m_pSession;
+    mxs_target_t m_use_sql_variables_in;
+    bool         m_load_active;
+};
+
+}