Bug#30671

  "ALTER SERVER can cause server to crash"
  While retrieving values, it would erronously set the socket value
  to NULL and attempt to use it in strcmp().
  Ensure it is correctly set to "" so that strcmp may not crash.

mysql-test/r/federated_server.result

@@ -253,6 +253,14 @@ drop user guest_usage@localhost;
 drop user guest_select@localhost;
 drop table federated.t1;
 drop server 's1';
+create server 's1' foreign data wrapper 'mysql' options (port 3306);
+alter server 's1' options
+(host 'localhost', database '', user '',
+password '', socket '', owner '', port 3306);
+alter server 's1' options
+(host 'localhost', database 'database1', user '',
+password '', socket '', owner '', port 3306);
+drop server 's1';
 # End of 5.1 tests
 use test;
 create procedure p1 ()
@@ -262,7 +270,7 @@ DECLARE e INT DEFAULT 0;
 DECLARE i INT;
 DECLARE CONTINUE HANDLER FOR SQLEXCEPTION SET e = e + 1;
 SET i = sleep(5);
-WHILE v < 20000 do
+WHILE v < 10000 do
 CREATE SERVER s
 FOREIGN DATA WRAPPER mysql
 OPTIONS (USER 'Remote', HOST '192.168.1.106', DATABASE 'test');

mysql-test/t/federated_server.test

@@ -2,7 +2,7 @@
 # if federated can utilise the servers table
 # should work with embedded server after mysqltest is fixed
 -- source include/not_embedded.inc
--- source include/federated.inc;
+-- source include/federated.inc
 -- source include/big_test.inc
 
 connection slave;
@@ -282,6 +282,18 @@ drop user guest_select@localhost;
 drop table federated.t1;
 drop server 's1';
 
+#
+# Bug#30671 - ALTER SERVER causes the server to crash
+#
+create server 's1' foreign data wrapper 'mysql' options (port 3306);
+alter server 's1' options
+  (host 'localhost', database '', user '',
+  password '', socket '', owner '', port 3306);
+# The next statement would crash unpatched server
+alter server 's1' options
+  (host 'localhost', database 'database1', user '',
+  password '', socket '', owner '', port 3306);
+drop server 's1';
 
 --echo # End of 5.1 tests
 

sql/sql_servers.cc

@@ -289,7 +289,7 @@ get_server_from_table_to_cache(TABLE *table)
 {
   /* alloc a server struct */
   char *ptr;
-  char *blank= (char*)"";
+  char * const blank= (char*)"";
   FOREIGN_SERVER *server= (FOREIGN_SERVER *)alloc_root(&mem,
                                                        sizeof(FOREIGN_SERVER));
   DBUG_ENTER("get_server_from_table_to_cache");
@@ -312,7 +312,7 @@ get_server_from_table_to_cache(TABLE *table)
   server->port= server->sport ? atoi(server->sport) : 0;
 
   ptr= get_field(&mem, table->field[6]);
-  server->socket= ptr && strlen(ptr) ? ptr : NULL;
+  server->socket= ptr && strlen(ptr) ? ptr : blank;
   ptr= get_field(&mem, table->field[7]);
   server->scheme= ptr ? ptr : blank;
   ptr= get_field(&mem, table->field[8]);