Replaced write system function with wrapper gw_write. It allows for generating failures by using telnet commands, fail backendfd, fail clientfd, which are available in debug build only.

server/modules/protocol/httpd.c

@@ -267,7 +267,9 @@ httpd_write_event(DCB *dcb)
 static int
 httpd_write(DCB *dcb, GWBUF *queue)
 {
-	return dcb_write(dcb, queue);
+        int rc;
+        rc = dcb_write(dcb, queue);
+	return rc;
 }
 
 /**

server/modules/protocol/mysql_backend.c

@@ -149,11 +149,10 @@ static int gw_read_backend_event(DCB *dcb) {
 
         CHK_DCB(dcb);        
 	CHK_SESSION(dcb->session);
-        ss_info_dassert(dcb->session != NULL,
-                        "Backend dcb doesn't have session");
         
         backend_protocol = (MySQLProtocol *) dcb->protocol;
-
+        CHK_PROTOCOL(backend_protocol);
+        
         /** return only with complete session */
         current_session = gw_get_shared_session_auth_info(dcb);
         ss_dassert(current_session != NULL);
@@ -180,7 +179,8 @@ static int gw_read_backend_event(DCB *dcb) {
                         	current_session->db,
                         	current_session->user,
                         	current_session->client_sha1,
-                        	backend_protocol) != 0) {
+                        	backend_protocol) != 0)
+                        {
 				backend_protocol->state = MYSQL_AUTH_FAILED;
                 		rc = 1;
 			} else {
@@ -411,6 +411,7 @@ static int
 gw_MySQLWrite_backend(DCB *dcb, GWBUF *queue)
 {
 	MySQLProtocol *backend_protocol = dcb->protocol;
+        int rc;
 
         /**
          * Don't write to backend if backend_dcb is not in poll set anymore.
@@ -444,8 +445,8 @@ gw_MySQLWrite_backend(DCB *dcb, GWBUF *queue)
         memcpy(&dcb->command, &queue->command, sizeof(dcb->command));
 
 	spinlock_release(&dcb->authlock);
-
-	return dcb_write(dcb, queue);
+        rc = dcb_write(dcb, queue);
+	return rc;
 }
 
 /**
@@ -631,6 +632,7 @@ static void backend_set_delayqueue(DCB *dcb, GWBUF *queue) {
 static int backend_write_delayqueue(DCB *dcb)
 {
 	GWBUF *localq = NULL;
+        int   rc;
 
 	spinlock_acquire(&dcb->delayqlock);
 
@@ -644,8 +646,8 @@ static int backend_write_delayqueue(DCB *dcb)
         memcpy(&dcb->command, &localq->command, sizeof(dcb->command));
 
 	spinlock_release(&dcb->delayqlock);
-
-	return dcb_write(dcb, localq);
+        rc = dcb_write(dcb, localq);
+	return rc;
 }
 
 

server/modules/protocol/mysql_client.c

@@ -461,7 +461,7 @@ int	w, saved_errno = 0;
 		{
 			len = GWBUF_LENGTH(queue);
 			GW_NOINTR_CALL(
-                                w = write(dcb->fd,GWBUF_DATA(queue), len);
+                                w = gw_write(dcb->fd,GWBUF_DATA(queue), len);
                                 dcb->stats.n_writes++);
 			saved_errno = errno;
 			if (w < 0)
@@ -642,12 +642,17 @@ int gw_read_client_event(DCB* dcb) {
                  /* len = GWBUF_LENGTH(queue); */
                 ptr_buff = GWBUF_DATA(queue);
                 
-                /* get mysql commang at fourth byte */
+                /* get mysql commang at fifth byte */
                 if (ptr_buff) {
                         mysql_command = ptr_buff[4];
                 }
 
                 if (mysql_command  == '\x03') {
+                        /**
+                         * SQL Trace here.
+                         * Length can be calculated and it must be passed as
+                         * argument.
+                         */
                         /* this is a standard MySQL query !!!! */
                 }
                 /**
@@ -716,27 +721,43 @@ return_rc:
 ///////////////////////////////////////////////
 // client write event to Client triggered by EPOLLOUT
 //////////////////////////////////////////////
+/** 
+ * @node Client's fd became writable, and EPOLLOUT event
+ * arrived. As a consequence, client input buffer (writeq) is flushed. 
+ *
+ * Parameters:
+ * @param dcb - in, use
+ *          client dcb
+ *
+ * @return constantly 1
+ *
+ * 
+ * @details (write detailed description here)
+ *
+ */
 int gw_write_client_event(DCB *dcb)
 {
 	MySQLProtocol *protocol = NULL;
 
         CHK_DCB(dcb);
 
+        ss_dassert(dcb->state != DCB_STATE_DISCONNECTED);
+        
 	if (dcb == NULL) {
 		fprintf(stderr, "DCB is NULL, return\n");
-		return 1;
+		goto return_1;
 	}
-        ss_dassert(dcb->state != DCB_STATE_DISCONNECTED);
 
 	if (dcb->state == DCB_STATE_DISCONNECTED) {
-		return 1;
+		goto return_1;
 	}
-	if (dcb->protocol) {
-		protocol = DCB_PROTOCOL(dcb, MySQLProtocol);
-	} else {
-                goto return_1;
+        
+	if (dcb->protocol == NULL) {
+	        goto return_1;
 	}
-
+        protocol = (MySQLProtocol *)dcb->protocol;
+        CHK_PROTOCOL(protocol);
+        
 	if (protocol->state == MYSQL_IDLE ||
             protocol->state == MYSQL_WAITING_RESULT)
         {

server/modules/protocol/mysql_common.c

@@ -504,7 +504,7 @@ int gw_send_authentication_to_backend(char *dbname, char *user, uint8_t *passwd,
 
 	// write to backend dcb
 	// ToDO: handle the EAGAIN | EWOULDBLOCK
-	rv = write(dcb->fd, GWBUF_DATA(buffer), bytes);
+	rv = gw_write(dcb->fd, GWBUF_DATA(buffer), bytes);
 
 	gwbuf_consume(buffer, bytes);
 

server/modules/protocol/telnetd.c

@@ -224,7 +224,9 @@ telnetd_write_event(DCB *dcb)
 static int
 telnetd_write(DCB *dcb, GWBUF *queue)
 {
-	return dcb_write(dcb, queue);
+        int rc;
+        rc = dcb_write(dcb, queue);
+	return rc;
 }
 
 /**