MDEV-21049 Segfault in create federatedx table with empty hostname

Use my_localhost instead of NULL for share->hostname.

mysql-test/suite/federated/federatedx.result

@@ -2283,6 +2283,22 @@ connection default;
 connection master;
 CREATE TABLE t1 (a INT) ENGINE=FEDERATED CONNECTION='mysql://@127.0.0.1:SLAVE_PORT/federated/t1';
 ERROR HY000: Can't create federated table. Foreign data src error:  database: 'federated'  username: ''  hostname: '127.0.0.1'
+#
+# MDEV-21049 Segfault in create federatedx table with empty hostname
+#
+connection master;
+CREATE TABLE federated.t1 (x int) ENGINE=FEDERATED
+CONNECTION='mysql://root@:SLAVE_PORT/federated/t1';
+ERROR HY000: Can't create federated table. Foreign data src error:  database: 'federated'  username: 'root'  hostname: 'localhost'
+connection slave;
+CREATE TABLE federated.t1(x int);
+connection master;
+CREATE TABLE federated.t1 (x int) ENGINE=FEDERATED
+CONNECTION='mysql://root@:SLAVE_PORT/federated/t1';
+DROP TABLE federated.t1;
+connection slave;
+DROP TABLE federated.t1;
+connection default;
 connection master;
 DROP TABLE IF EXISTS federated.t1;
 DROP DATABASE IF EXISTS federated;

mysql-test/suite/federated/federatedx.test

@@ -2010,4 +2010,25 @@ connection master;
 --error ER_CANT_CREATE_FEDERATED_TABLE
 eval CREATE TABLE t1 (a INT) ENGINE=FEDERATED CONNECTION='mysql://@127.0.0.1:$SLAVE_MYPORT/federated/t1';
 
+--echo #
+--echo # MDEV-21049 Segfault in create federatedx table with empty hostname
+--echo #
+connection master;
+--replace_result $SLAVE_MYPORT SLAVE_PORT
+--error ER_CANT_CREATE_FEDERATED_TABLE
+eval CREATE TABLE federated.t1 (x int) ENGINE=FEDERATED
+  CONNECTION='mysql://root@:$SLAVE_MYPORT/federated/t1';
+
+connection slave;
+CREATE TABLE federated.t1(x int);
+connection master;
+--replace_result $SLAVE_MYPORT SLAVE_PORT
+eval CREATE TABLE federated.t1 (x int) ENGINE=FEDERATED
+  CONNECTION='mysql://root@:$SLAVE_MYPORT/federated/t1';
+
+DROP TABLE federated.t1;
+connection slave;
+DROP TABLE federated.t1;
+connection default;
+
 source include/federated_cleanup.inc;

storage/federatedx/ha_federatedx.cc

@@ -798,12 +798,12 @@ static int parse_url(MEM_ROOT *mem_root, FEDERATEDX_SHARE *share,
       goto error;
 
     if (share->hostname[0] == '\0')
-      share->hostname= NULL;
+      share->hostname= strdup_root(mem_root, my_localhost);
 
   }
   if (!share->port)
   {
-    if (!share->hostname || strcmp(share->hostname, my_localhost) == 0)
+    if (0 == strcmp(share->hostname, my_localhost))
       share->socket= (char *) MYSQL_UNIX_ADDR;
     else
       share->port= MYSQL_PORT;
@@ -3385,8 +3385,7 @@ int ha_federatedx::create(const char *name, TABLE *table_arg,
     goto error;
 
   /* loopback socket connections hang due to LOCK_open mutex */
-  if ((!tmp_share.hostname || !strcmp(tmp_share.hostname,my_localhost)) &&
-      !tmp_share.port)
+  if (0 == strcmp(tmp_share.hostname, my_localhost) && !tmp_share.port)
     goto error;
 
   /*