Move RWBackend into a separate file

Moved the RWBackend class implementation into its own file. Made some of
the command type functions a part of the <maxscale/protocol/mysql.h>
header to make it reusable.

server/modules/routing/readwritesplit/rwbackend.hh

@@ -0,0 +1,91 @@
+#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 <map>
+#include <tr1/memory>
+
+#include <maxscale/backend.hh>
+
+namespace maxscale
+{
+
+/** Enum for tracking client reply state */
+enum reply_state_t
+{
+    REPLY_STATE_START,          /**< Query sent to backend */
+    REPLY_STATE_DONE,           /**< Complete reply received */
+    REPLY_STATE_RSET_COLDEF,    /**< Resultset response, waiting for column definitions */
+    REPLY_STATE_RSET_ROWS       /**< Resultset response, waiting for rows */
+};
+
+typedef std::map<uint32_t, uint32_t> BackendHandleMap; /** Internal ID to external ID */
+
+class RWBackend: public mxs::Backend
+{
+    RWBackend(const RWBackend&);
+    RWBackend& operator=(const RWBackend&);
+
+public:
+    RWBackend(SERVER_REF* ref);
+    ~RWBackend();
+
+    inline reply_state_t get_reply_state() const
+    {
+        return m_reply_state;
+    }
+
+    inline void set_reply_state(reply_state_t state)
+    {
+        m_reply_state = state;
+    }
+
+    void add_ps_handle(uint32_t id, uint32_t handle);
+    uint32_t get_ps_handle(uint32_t id) const;
+
+    bool execute_session_command();
+    bool write(GWBUF* buffer, response_type type = EXPECT_RESPONSE);
+    void close(close_type type = CLOSE_NORMAL);
+
+    inline void set_large_packet(bool value)
+    {
+        m_large_packet = value;
+    }
+
+    inline bool is_large_packet() const
+    {
+        return m_large_packet;
+    }
+
+    inline uint8_t current_command() const
+    {
+        return m_command;
+    }
+
+    bool reply_is_complete(GWBUF *buffer);
+
+private:
+    reply_state_t    m_reply_state;
+    BackendHandleMap m_ps_handles; /**< Internal ID to backend PS handle mapping */
+    bool             m_large_packet; /**< Used to store the state of the EOF packet
+                                      *calculation for result sets when the result
+                                      * contains very large rows */
+    uint8_t          m_command;
+};
+
+typedef std::tr1::shared_ptr<RWBackend> SRWBackend;
+typedef std::list<SRWBackend> SRWBackendList;
+
+}