MXS-1343: send hostname to master with COM_REGISTER_SLAVE

A new option ‘slave_hostname’ allows the setting of hostname in
COM_REGISTER_SLAVE.

SHOW SLAVES HOSTS; in master server can show the hostname set in binlog
router:

MariaDB [(none)]> SHOW SLAVE HOSTS;
+-----------+-----------------------------+------+-----------+
| Server_id | Host                        | Port | Master_id |
+-----------+-----------------------------+------+-----------+
|        93 | maxscale-blr-1.mydomain.net | 8808 |     10124 |
+-----------+-----------------------------+------+-----------+

server/modules/routing/binlogrouter/blr.c

@@ -184,6 +184,7 @@ MXS_MODULE* MXS_CREATE_MODULE()
             {"master_uuid", MXS_MODULE_PARAM_STRING},
             {"master_version", MXS_MODULE_PARAM_STRING},
             {"master_hostname", MXS_MODULE_PARAM_STRING},
+            {"slave_hostname", MXS_MODULE_PARAM_STRING},
             {"mariadb10-compatibility", MXS_MODULE_PARAM_BOOL, "false"},
             {"filestem", MXS_MODULE_PARAM_STRING, BINLOG_NAME_ROOT},
             {"file", MXS_MODULE_PARAM_COUNT, "1"},
@@ -334,6 +335,7 @@ createInstance(SERVICE *service, char **options)
     inst->trx_safe = config_get_bool(params, "transaction_safety");
     inst->set_master_version = config_copy_string(params, "master_version");
     inst->set_master_hostname = config_copy_string(params, "master_hostname");
+    inst->set_slave_hostname = config_copy_string(params, "slave_hostname");
     inst->fileroot = config_copy_string(params, "filestem");
 
     inst->serverid = config_get_integer(params, "server_id");
@@ -344,8 +346,6 @@ createInstance(SERVICE *service, char **options)
     inst->master_uuid = config_copy_string(params, "master_uuid");
     inst->set_master_uuid = inst->master_uuid != NULL;
 
-    inst->set_master_version = NULL;
-    inst->set_master_hostname = NULL;
     inst->send_slave_heartbeat = config_get_bool(params, "send_slave_heartbeat");
 
     /* Semi-Sync support */
@@ -482,6 +482,11 @@ createInstance(SERVICE *service, char **options)
                     MXS_FREE(inst->set_master_hostname);
                     inst->set_master_hostname = MXS_STRDUP_A(value);
                 }
+                else if (strcmp(options[i], "slave_hostname") == 0)
+                {
+                    MXS_FREE(inst->set_slave_hostname);
+                    inst->set_slave_hostname = MXS_STRDUP_A(value);
+                }
                 else if (strcmp(options[i], "mariadb10-compatibility") == 0)
                 {
                     inst->mariadb10_compat = config_truth_value(value);
@@ -938,6 +943,7 @@ free_instance(ROUTER_INSTANCE *instance)
     MXS_FREE(instance->password);
     MXS_FREE(instance->set_master_version);
     MXS_FREE(instance->set_master_hostname);
+    MXS_FREE(instance->set_slave_hostname);
     MXS_FREE(instance->fileroot);
     MXS_FREE(instance->binlogdir);
     /* SSL options */

server/modules/routing/binlogrouter/blr.h

@@ -592,6 +592,7 @@ typedef struct router_instance
     int               master_semi_sync;     /*< Semi-Sync replication status of master server */
     BINLOG_ENCRYPTION_SETUP encryption;     /*< Binlog encryption setup */
     void              *encryption_ctx;      /*< Encryption context */
+    char              *set_slave_hostname;  /*< Send custom Hostname to Master */
     struct router_instance  *next;
 } ROUTER_INSTANCE;
 

server/modules/routing/binlogrouter/blr_master.c

@@ -885,28 +885,55 @@ blr_make_registration(ROUTER_INSTANCE *router)
 {
     GWBUF *buf;
     unsigned char *data;
-    int len = 18;
+    int len = 18;    // Min size of COM_REGISTER_SLAVE payload
     int port = 3306;
+    int hostname_len = 0;
 
-    if ((buf = gwbuf_alloc(len + 4)) == NULL)
+    // Send router->set_slave_hostname
+    if (router->set_slave_hostname && router->set_slave_hostname[0])
+    {
+        hostname_len = strlen(router->set_slave_hostname);
+    }
+
+    // Add hostname len
+    len += hostname_len;
+
+    if ((buf = gwbuf_alloc(len + MYSQL_HEADER_LEN)) == NULL)
     {
         return NULL;
     }
+
     data = GWBUF_DATA(buf);
     encode_value(&data[0], len, 24); // Payload length
     data[3] = 0;                     // Sequence ID
     data[4] = COM_REGISTER_SLAVE;    // Command
     encode_value(&data[5], router->serverid, 32);   // Slave Server ID
-    data[9] = 0;                     // Slave hostname length
+
-    data[10] = 0;                    // Slave username length
+    // Point to hostname len offset
-    data[11] = 0;                    // Slave password length
+    data += 9;
+
+    *data++ = hostname_len;               // Slave hostname length
+
+    // Copy hostname
+    if (hostname_len)
+    {
+        memcpy(data, router->set_slave_hostname, hostname_len);
+    }
+
+    // Point to user
+    data += hostname_len;
+    // Set empty user
+    *data++ = 0;           // Slave username length
+    // Set empty password
+    *data++ = 0;           // Slave password length
+    // Add port
     if (router->service->ports)
     {
         port = router->service->ports->port;
     }
-    encode_value(&data[12], port, 16);  // Slave master port
+    encode_value(&data[0], port, 16);               // Slave master port, 2 bytes
-    encode_value(&data[14], 0, 32);         // Replication rank
+    encode_value(&data[2], 0, 32);                  // Replication rank, 4 bytes
-    encode_value(&data[18], router->masterid, 32);  // Master server-id
+    encode_value(&data[6], router->masterid, 32);   // Master server-id, 4 bytes
 
     // This is hack to get the result set processing in order for binlogrouter
     MySQLProtocol *proto = (MySQLProtocol*)router->master->protocol;
@@ -2202,9 +2229,15 @@ static void blr_log_identity(ROUTER_INSTANCE *router)
 
     /* Seen by the master */
     MXS_NOTICE("%s: identity seen by the master: "
-               "server_id: %d, uuid: %s",
+               "Server_id: %d, Slave_UUID: %s, Host: %s",
                router->service->name,
-               router->serverid, (router->uuid == NULL ? "not available" : router->uuid));
+               router->serverid,
+               router->uuid == NULL ?
+               "not available" :
+               router->uuid,
+               (router->set_slave_hostname && router->set_slave_hostname[0]) ?
+               router->set_slave_hostname :
+               "not set");
 
     /* Seen by the slaves */