MXS-2485 PacketTracker utility class.

Several TODOs in PacketTracker.

maxutils/maxsql/include/maxsql/CMakeLists.txt

@@ -1,3 +1,4 @@
 install_header(mariadb.hh devel)
 install_header(ccdefs.hh devel)
-
+install_header(packet_tracker.hh devel)
+install_header(mysql_plus.hh devel)

maxutils/maxsql/include/maxsql/packet_tracker.hh

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2019 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: 2022-01-01
+ *
+ * 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.
+ */
+
+#pragma once
+
+#include <maxscale/ccdefs.hh>
+
+struct GWBUF;
+
+namespace maxsql
+{
+
+class ComResponse;
+
+// Minimal class to track the lifetime of a query.
+// TODO add documentation
+class PacketTracker
+{
+public:
+    enum class State {FirstPacket, Field, FieldEof, ComFieldList, Row, Done, ErrorPacket, Error};
+
+    PacketTracker() = default;
+    explicit PacketTracker(GWBUF* pQuery);      // Track this query
+
+    void  update(GWBUF* pPacket);       // Update as packets are received.
+    State state() const;
+    bool  expecting_more_packets() const;
+
+private:
+    // State functions.
+    State first_packet(const ComResponse& com_packet);
+    State field(const ComResponse& com_packet);
+    State field_eof(const ComResponse& com_packet);
+    State com_field_list(const ComResponse& com_packet);
+    State row(const ComResponse& com_packet);
+    State expect_no_more(const ComResponse& com_packet);        // states: Done, ErrorPacket, Error
+
+    State m_state = State::Error;
+    bool  m_client_packet_bool = false;
+    bool  m_server_packet_bool = false;
+
+    int m_command;
+    int m_total_fields;
+    int m_field_count;
+};
+
+inline PacketTracker::State PacketTracker::state() const
+{
+    return m_state;
+}
+
+std::ostream& operator<<(std::ostream&, PacketTracker::State state);
+}