Complementary fix to #694,http://bugs.mariadb.com/show_bug.cgi?id=694

RWSplit router handles query processing errors that happened in router by sending parse error reply to client. routeQuery fails only when backend has failed.

server/core/modutil.c

@@ -32,6 +32,19 @@
 #include <string.h>
 #include <mysql_client_server_protocol.h>
 #include <modutil.h>
+
+/** Defined in log_manager.cc */
+extern int            lm_enabled_logfiles_bitmask;
+extern size_t         log_ses_count[];
+extern __thread log_info_t tls_log_info;
+
+static void modutil_reply_routing_error(
+	DCB*  backend_dcb,
+	int   error,
+	char* state,
+	char* errstr);
+
+
 /**
  * Check if a GWBUF structure is a MySQL COM_QUERY packet
  *
@@ -327,7 +340,7 @@ GWBUF *modutil_create_mysql_err_msg(
 	const char	*msg)
 {
 	uint8_t		*outbuf = NULL;
-	uint32_t		mysql_payload_size = 0;
+	uint32_t	mysql_payload_size = 0;
 	uint8_t		mysql_packet_header[4];
 	uint8_t		*mysql_payload = NULL;
 	uint8_t		field_count = 0;
@@ -528,7 +541,7 @@ modutil_count_signal_packets(GWBUF *reply, int use_ok, int n_found)
     unsigned char* ptr = (unsigned char*) reply->start;
     unsigned char* end = (unsigned char*) reply->end;
     unsigned char* prev = ptr;
-    int pktlen, eof = 0, err = 0, found = n_found;
+    int pktlen, eof = 0, err = 0;
     int errlen = 0, eoflen = 0;
     int iserr = 0, iseof = 0;
     while(ptr < end)
@@ -583,3 +596,57 @@ modutil_count_signal_packets(GWBUF *reply, int use_ok, int n_found)
 
     return(eof + err);
 }
+
+/**
+ * Create parse error and EPOLLIN event to event queue of the backend DCB.
+ * When event is notified the error message is processed as error reply and routed 
+ * upstream to client.
+ * 
+ * @param backend_dcb	DCB where event is added
+ * @param errstr	Plain-text string error
+ */
+void modutil_reply_parse_error(
+	DCB*  backend_dcb,
+	char* errstr)
+{
+	CHK_DCB(backend_dcb);
+	modutil_reply_routing_error(backend_dcb, 1064, "42000", errstr);
+}
+
+/**
+ * Create error message and EPOLLIN event to event queue of the backend DCB.
+ * When event is notified the message is processed as error reply and routed 
+ * upstream to client.
+ * 
+ * @param backend_dcb	DCB where event is added
+ * @param error		SQL error number
+ * @param state		SQL state
+ * @param errstr	Plain-text string error
+ */
+static void modutil_reply_routing_error(
+	DCB*  backend_dcb,
+	int   error,
+	char* state,
+	char* errstr)
+{
+	GWBUF* buf;
+	CHK_DCB(backend_dcb);
+	
+	buf = modutil_create_mysql_err_msg(1, 0, error, state, errstr);
+	free(errstr);
+	
+	if (buf == NULL)
+	{
+		LOGIF(LE, (skygw_log_write_flush(
+			LOGFILE_ERROR,
+			"Error : Creating buffer for error message failed."))); 
+		return;
+	}
+	/** Set flags that help router to identify session commands reply */
+	gwbuf_set_type(buf, GWBUF_TYPE_MYSQL);
+	gwbuf_set_type(buf, GWBUF_TYPE_SESCMD_RESPONSE);
+	gwbuf_set_type(buf, GWBUF_TYPE_RESPONSE_END);
+	/** Create an incoming event for backend DCB */
+	poll_add_epollin_event_to_dcb(backend_dcb, buf);
+	return;
+}

server/include/modutil.h

@@ -50,6 +50,7 @@ extern int	modutil_send_mysql_err_packet(DCB *, int, int, int, const char *, con
 GWBUF* 		modutil_get_next_MySQL_packet(GWBUF** p_readbuf);
 GWBUF*          modutil_get_complete_packets(GWBUF** p_readbuf);
 int 		modutil_MySQL_query_len(GWBUF* buf, int* nbytes_missing);
+void 		modutil_reply_parse_error(DCB* backend_dcb, char* errstr);
 
 GWBUF *modutil_create_mysql_err_msg(
 	int		packet_number,

server/include/router.h

@@ -43,6 +43,11 @@
  */
 typedef void *ROUTER;
 
+typedef enum error_action {
+	ERRACT_NEW_CONNECTION = 0x001,
+	ERRACT_REPLY_CLIENT   = 0x002,
+	ERRACT_RESET	      = 0x004
+} error_action_t;
 
 /**
  * @verbatim
@@ -66,13 +71,6 @@ typedef void *ROUTER;
  *
  * @see load_module
  */
-typedef enum error_action {
-        ERRACT_NEW_CONNECTION = 0x001,
-        ERRACT_REPLY_CLIENT   = 0x002,
-	ERRACT_RESET	      = 0x004
-} error_action_t;
-
-
 typedef struct router_object {
 	ROUTER	*(*createInstance)(SERVICE *service, char **options);
 	void	*(*newSession)(ROUTER *instance, SESSION *session);

server/modules/protocol/mysql_backend.c

@@ -358,7 +358,6 @@ static int gw_read_backend_event(DCB *dcb) {
                                                 GWBUF_LENGTH(dcb->delayq))) != NULL);
                                 }
                                 spinlock_release(&dcb->delayqlock);                                
-                                
                                 {
                                         GWBUF* errbuf;
                                         bool   succp;
@@ -1464,7 +1463,7 @@ static int gw_change_user(
 			rv = 0;
 			goto retblock;			
 		}
-		/** Set flags that help router to identify session commans reply */
+		/** Set flags that help router to identify session commands reply */
 		gwbuf_set_type(buf, GWBUF_TYPE_MYSQL);
 		gwbuf_set_type(buf, GWBUF_TYPE_SESCMD_RESPONSE);
 		gwbuf_set_type(buf, GWBUF_TYPE_RESPONSE_END);

server/modules/protocol/mysql_client.c

@@ -865,7 +865,7 @@ int gw_read_client_event(
                                 rc = SESSION_ROUTE_QUERY(session, read_buffer);
                         }
                                        
-                        /** succeed */
+                        /** Routing succeed */
                         if (rc)
 			{
                                 rc = 0; /**< here '0' means success */
@@ -874,25 +874,6 @@ int gw_read_client_event(
 			{
 				bool   succp;
 				GWBUF* errbuf;
-
-				/** 
-				 * Create error to be sent to client if session
-				 * can't be continued.
-				 */
-				errbuf = mysql_create_custom_error(
-					1, 
-					0, 
-				       "Routing query to backend failed. See "
-				       "the error log for further details.");
-				
-				router->handleError(
-						router_instance,
-						session->router_session, 
-						errbuf, 
-						dcb,
-						ERRACT_REPLY_CLIENT,
-						&succp);
-				free(errbuf);
 				/** 
 				 * Create error to be sent to client if session
 				 * can't be continued.

server/modules/routing/readwritesplit/readwritesplit.c

@@ -1972,7 +1972,16 @@ retblock:
 }
 
 
-
+/**
+ * Routing function. Find out query type, backend type, and target DCB(s). 
+ * Then route query to found target(s).
+ * @param inst		router instance
+ * @param rses		router session
+ * @param querybuf	GWBUF including the query
+ * 
+ * @return true if routing succeed or if it failed due to unsupported query.
+ * false if backend failure was encountered.
+ */
 static bool route_single_stmt(
 	ROUTER_INSTANCE*   inst,
 	ROUTER_CLIENT_SES* rses,
@@ -2162,6 +2171,8 @@ static bool route_single_stmt(
 		if (TARGET_IS_MASTER(route_target) || 
 			TARGET_IS_SLAVE(route_target))
 		{
+			backend_ref_t* bref = rses->rses_backend_ref;
+			
 			char* query_str = modutil_get_query(querybuf);
 			char* qtype_str = skygw_get_qtype_str(qtype);
 			
@@ -2181,9 +2192,22 @@ static bool route_single_stmt(
 						   "modification from other "
 						   "servers. <")));
 			
+			while (bref != NULL && !BREF_IS_IN_USE(bref))
+			{
+				bref++;
+			}
+			
+			if (bref != NULL && BREF_IS_IN_USE(bref))
+			{
+				modutil_reply_parse_error(
+					bref->bref_dcb,
+					strdup("Routing query to backend failed. "
+					"See the error log for further "
+					"details."));
+			}			
 			if (query_str) free (query_str);
 			if (qtype_str) free(qtype_str);
-			succp = false;
+			succp = true;
 			goto retblock;
 		}
 		/**