Track session autocommit state

This tracks only what is explicitly set. That is, if autocommit
has been set true then, even if a transaction is started, autocommit
will not be set false.

That is, a user of the session autocommit and transaction states
need to be aware of their semantics. If a transaction is active,
then the state of autocommit is irrelevant.

include/maxscale/session.h

@@ -181,6 +181,7 @@ typedef struct session
     int             refcount;         /*< Reference count on the session */
     bool            ses_is_child;     /*< this is a child session */
     session_trx_state_t trx_state;    /*< The current transaction state. */
+    bool            autocommit;       /*< Whether autocommit is on. */
     skygw_chk_t     ses_chk_tail;
 } SESSION;
 
@@ -289,6 +290,41 @@ static inline bool session_trx_is_read_write(const SESSION* ses)
     return ses->trx_state == SESSION_TRX_READ_WRITE;
 }
 
+/**
+ * Tells whether autocommit is ON or not.
+ *
+ * Note that the returned value effectively only tells the last value
+ * of the statement "set autocommit=...".
+ *
+ * That is, if the statement "set autocommit=1" has been executed, then
+ * even if a transaction has been started, which implicitly will cause
+ * autocommit to be set to 0 for the duration of the transaction, this
+ * function will still return true.
+ *
+ * Note also that by default autocommit is ON.
+ *
+ * @return True if autocommit has been set ON, false otherwise.
+ */
+static inline bool session_is_autocommit(const SESSION* ses)
+{
+    return ses->autocommit;
+}
+
+/**
+ * Sets the autocommit state of the session.
+ *
+ * NOTE: Only the protocol object may call this.
+ *
+ * @param enable True if autocommit is enabled, false otherwise.
+ * @return The previous state.
+ */
+static inline bool session_set_autocommit(SESSION* ses, bool autocommit)
+{
+    bool prev_autocommit = ses->autocommit;
+    ses->autocommit = autocommit;
+    return prev_autocommit;
+}
+
 MXS_END_DECLS
 
 #endif

server/core/session.c

@@ -143,6 +143,7 @@ session_alloc(SERVICE *service, DCB *client_dcb)
     session->state = SESSION_STATE_READY;
 
     session->trx_state = SESSION_TRX_UNKNOWN;
+    session->autocommit = true;
     /*
      * Only create a router session if we are not the listening
      * DCB or an internal DCB. Creating a router session may create a connection to a

server/modules/protocol/MySQL/MySQLClient/mysql_client.c

@@ -916,6 +916,14 @@ gw_read_finish_processing(DCB *dcb, GWBUF *read_buffer, uint64_t capabilities)
         {
             session_set_trx_state(ses, SESSION_TRX_INACTIVE);
         }
+        else if (type & QUERY_TYPE_ENABLE_AUTOCOMMIT)
+        {
+            session_set_autocommit(ses, true);
+        }
+        else if (type & QUERY_TYPE_DISABLE_AUTOCOMMIT)
+        {
+            session_set_autocommit(ses, false);
+        }
 
         /**
          * Feed each statement completely and separately