Allow collection of prepared statement responses

The backend MySQL protocol can now collect prepared statement preparation
responses as well as result sets. This removes the need to parse and
collect the preparation responses at the router level.

include/maxscale/protocol/mysql.h

@@ -95,6 +95,21 @@ MXS_BEGIN_DECLS
 #define GW_MYSQL_SCRAMBLE_SIZE 20
 #define GW_SCRAMBLE_LENGTH_323 8
 
+/**
+ * Prepared statement payload response offsets for a COM_STMT_PREPARE response:
+ *
+ * [0]     OK (1)            -- always 0x00
+ * [1-4]   statement_id (4)  -- statement-id
+ * [5-6]   num_columns (2)   -- number of columns
+ * [7-8]   num_params (2)    -- number of parameters
+ * [9]     filler
+ * [10-11] warning_count (2) -- number of warnings
+ */
+#define MYSQL_PS_ID_OFFSET     MYSQL_HEADER_LEN + 1
+#define MYSQL_PS_COLS_OFFSET   MYSQL_HEADER_LEN + 5
+#define MYSQL_PS_PARAMS_OFFSET MYSQL_HEADER_LEN + 7
+#define MYSQL_PS_WARN_OFFSET   MYSQL_HEADER_LEN + 10
+
 /** Name of the default server side authentication plugin */
 #define DEFAULT_MYSQL_AUTH_PLUGIN "mysql_native_password"
 
@@ -437,6 +452,15 @@ bool mxs_mysql_is_ok_packet(GWBUF *buffer);
  */
 bool mxs_mysql_is_result_set(GWBUF *buffer);
 
+/**
+ * @brief Check if the buffer contains a prepared statement OK packet
+ *
+ * @param buffer Buffer to check
+ *
+ * @return True if the @c buffer contains a prepared statement OK packet
+ */
+bool mxs_mysql_is_prep_stmt_ok(GWBUF *buffer);
+
 /**
  * @brief Check if the OK packet is followed by another result
  *