MXS-199: Support Causal Read in Read Write Splitting (#164)

* MXS-199: Support Causal Read in Read Write Splitting

* move most causal read logic into rwsplit router and get server type from monitor

* misc fix: remove new line

* refactor, move config to right place, replace ltrim with gwbuf_consume

* refacter a little for previous commit

* fix code style

include/maxscale/buffer.h

@@ -423,4 +423,16 @@ extern void dprintAllBuffers(void *pdcb);
  */
 void gwbuf_hexdump(GWBUF* buffer);
 
+/**
+ * Return pointer of the byte at offset from start of chained buffer
+ * Warning: It not guaranteed to point to a contiguous segment of memory,
+ * it is only safe to modify the first byte this pointer point to.
+ *
+ * @param buffer  one or more chained buffer
+ * @param offset  Offset into the buffer
+ * @return  if total buffer length is bigger than offset then return
+ *      the offset byte pointer, otherwise return null
+ */
+extern uint8_t *gwbuf_byte_pointer(GWBUF* buffer, size_t offset);
+
 MXS_END_DECLS

include/maxscale/server.h

@@ -75,6 +75,12 @@ typedef struct server_version
     uint32_t patch;
 } SERVER_VERSION;
 
+typedef enum
+{
+    SERVER_TYPE_MARIADB,
+    SERVER_TYPE_MYSQL
+} server_type_t;
+
 static inline void server_decode_version(uint64_t version, SERVER_VERSION* server_version)
 {
     uint32_t major = version / 10000;
@@ -120,6 +126,7 @@ typedef struct server
     struct  server *nextdb;        /**< Next server in list attached to a service */
     char           version_string[MAX_SERVER_VERSION_LEN]; /**< Server version string, i.e. MySQL server version */
     uint64_t       version;        /**< Server version */
+    server_type_t  server_type;    /**< Server type */
     long           node_id;        /**< Node id, server_id for M/S or local_index for Galera */
     int            rlag;           /**< Replication Lag for Master / Slave replication */
     unsigned long  node_ts;        /**< Last timestamp set from M/S monitor module */