Fixed crash in connect.misc with embedded server

The problem was that connect tried to recusiverly call
emb_advanced_command(), which was not supported.

Fixed by adding support for recursive calls.

libmysqld/embedded_priv.h

@@ -23,6 +23,8 @@ void init_embedded_mysql(MYSQL *mysql, ulong client_flag);
 void *create_embedded_thd(ulong client_flag);
 int check_embedded_connection(MYSQL *mysql, const char *db);
 void free_old_query(MYSQL *mysql);
+THD *embedded_get_current_thd();
+void embedded_set_current_thd(THD *thd);
 extern MYSQL_METHODS embedded_methods;
 
 /* This one is used by embedded library to gather returning data */

libmysqld/lib_sql.cc

@@ -111,7 +111,7 @@ emb_advanced_command(MYSQL *mysql, enum enum_server_command command,
                      MYSQL_STMT *stmt)
 {
   my_bool result= 1;
-  THD *thd=(THD *) mysql->thd;
+  THD *thd=(THD *) mysql->thd, *old_current_thd= current_thd;
   NET *net= &mysql->net;
   my_bool stmt_skip= stmt ? stmt->state != MYSQL_STMT_INIT_DONE : FALSE;
 
@@ -122,6 +122,8 @@ emb_advanced_command(MYSQL *mysql, enum enum_server_command command,
     else
     {
       free_embedded_thd(mysql);
+      if (old_current_thd == thd)
+        old_current_thd= 0;
       thd= 0;
     }
   }
@@ -179,6 +181,8 @@ emb_advanced_command(MYSQL *mysql, enum enum_server_command command,
 
 end:
   thd->reset_globals();
+  if (old_current_thd)
+    old_current_thd->store_globals();
   return result;
 }
 
@@ -432,12 +436,15 @@ int emb_unbuffered_fetch(MYSQL *mysql, char **row)
 
 static void free_embedded_thd(MYSQL *mysql)
 {
-  THD *thd= (THD*)mysql->thd;
+  THD *thd= (THD*)mysql->thd, *org_current_thd= current_thd;
   server_threads.erase(thd);
   thd->clear_data_list();
   thd->store_globals();
   delete thd;
-  set_current_thd(nullptr);
+  if (thd == org_current_thd)
+    set_current_thd(nullptr);
+  else
+    set_current_thd(org_current_thd);
   mysql->thd=0;
 }
 
@@ -727,6 +734,17 @@ void *create_embedded_thd(ulong client_flag)
 }
 
 
+THD *embedded_get_current_thd()
+{
+  return current_thd;
+}
+
+void embedded_set_current_thd(THD *thd)
+{
+  set_current_thd(thd);
+}
+
+
 #ifdef NO_EMBEDDED_ACCESS_CHECKS
 static void
 emb_transfer_connect_attrs(MYSQL *mysql)

libmysqld/libmysqld.c

@@ -78,7 +78,7 @@ mysql_real_connect(MYSQL *mysql,const char *host, const char *user,
 		   uint port, const char *unix_socket,ulong client_flag)
 {
   char name_buff[USERNAME_LENGTH];
-
+  THD *org_current_thd= embedded_get_current_thd();
   DBUG_ENTER("mysql_real_connect");
   DBUG_PRINT("enter",("host: %s  db: %s  user: %s (libmysqld)",
 		      host ? host : "(Null)",
@@ -200,6 +200,7 @@ mysql_real_connect(MYSQL *mysql,const char *host, const char *user,
       }
     }
   }
+  embedded_set_current_thd(org_current_thd);
 
   DBUG_PRINT("exit",("Mysql handler: %p", mysql));
   DBUG_RETURN(mysql);
@@ -216,6 +217,7 @@ mysql_real_connect(MYSQL *mysql,const char *host, const char *user,
     mysql_close(mysql);
     mysql->free_me=free_me;
   }
+  embedded_set_current_thd(org_current_thd);
   DBUG_RETURN(0);
 }