Bug #29878 Garbage data generation when executing SESSION_USER() on a slave.

Item_func_user doesn't calculate anything in it's val_str() method,
just returns saved str_value.
Though Item::save_in_field method can destroy str_value, relying on
val_str() return. As a result we get the garbage stored in field.

We cannot use Item::save_in_field implementation for Item_func_user,
reimplement it in simpler way.

mysql-test/r/rpl_session_var.result

@@ -41,3 +41,13 @@ select * from t2 order by b;
 b	a
 1	1
 drop table t1,t2;
+CREATE TABLE t1 (
+`id` int(11) NOT NULL auto_increment,
+`data` varchar(100),
+PRIMARY KEY  (`id`)
+) ENGINE=MyISAM;
+INSERT INTO t1(data) VALUES(SESSION_USER());
+SELECT * FROM t1;
+id	data
+1	
+drop table t1;

mysql-test/t/rpl_session_var.test

@@ -40,3 +40,25 @@ drop table t1,t2;
 save_master_pos;
 connection slave;
 sync_with_master;
+
+#
+# Bug #29878 Garbage data generation when executing SESSION_USER() on a slave. 
+#
+
+connection master;
+CREATE TABLE t1 (
+  `id` int(11) NOT NULL auto_increment,
+  `data` varchar(100),
+  PRIMARY KEY  (`id`)
+ ) ENGINE=MyISAM;
+
+INSERT INTO t1(data) VALUES(SESSION_USER());
+save_master_pos;
+connection slave;
+sync_with_master;
+SELECT * FROM t1;
+connection master;
+drop table t1;
+save_master_pos;
+connection slave;
+sync_with_master;

sql/item.cc

@@ -336,6 +336,37 @@ int Item::save_date_in_field(Field *field)
 }
 
 
+/*
+  Store the string value in field directly
+
+  SYNOPSIS
+    Item::save_str_value_in_field()
+    field   a pointer to field where to store
+    result  the pointer to the string value to be stored
+
+  DESCRIPTION
+    The method is used by Item_*::save_in_field implementations
+    when we don't need to calculate the value to store
+    See Item_string::save_in_field() implementation for example
+
+  IMPLEMENTATION
+    Check if the Item is null and stores the NULL or the
+    result value in the field accordingly.
+
+  RETURN
+    Nonzero value if error
+*/
+
+int Item::save_str_value_in_field(Field *field, String *result)
+{
+  if (null_value)
+    return set_field_to_null(field);
+  field->set_notnull();
+  return field->store(result->ptr(), result->length(),
+		      collation.collation);
+}
+
+
 Item::Item():
   rsize(0), name(0), orig_name(0), name_length(0), fixed(0),
   is_autogenerated_name(TRUE),
@@ -3009,16 +3040,6 @@ my_decimal *Item_copy_string::val_decimal(my_decimal *decimal_value)
 }
 
 
-
-int Item_copy_string::save_in_field(Field *field, bool no_conversions)
-{
-  if (null_value)
-    return set_field_to_null(field);
-  field->set_notnull();
-  return field->store(str_value.ptr(),str_value.length(),
-		      collation.collation);
-}
-
 /*
   Functions to convert item to field (for send_fields)
 */
@@ -4417,6 +4438,12 @@ int Item_null::save_safe_in_field(Field *field)
 }
 
 
+/*
+  This implementation can lose str_value content, so if the
+  Item uses str_value to store something, it should
+  reimplement it's ::save_in_field() as Item_string, for example, does
+*/
+
 int Item::save_in_field(Field *field, bool no_conversions)
 {
   int error;
@@ -4474,10 +4501,7 @@ int Item_string::save_in_field(Field *field, bool no_conversions)
 {
   String *result;
   result=val_str(&str_value);
-  if (null_value)
-    return set_field_to_null(field);
-  field->set_notnull();
-  return field->store(result->ptr(),result->length(),collation.collation);
+  return save_str_value_in_field(field, result);
 }
 
 

sql/item.h

@@ -612,6 +612,7 @@ class Item {
 
   int save_time_in_field(Field *field);
   int save_date_in_field(Field *field);
+  int save_str_value_in_field(Field *field, String *result);
 
   virtual Field *get_tmp_table_field() { return 0; }
   /* This is also used to create fields in CREATE ... SELECT: */
@@ -2166,7 +2167,10 @@ class Item_copy_string :public Item
   my_decimal *val_decimal(my_decimal *);
   void make_field(Send_field *field) { item->make_field(field); }
   void copy();
-  int save_in_field(Field *field, bool no_conversions);
+  int save_in_field(Field *field, bool no_conversions)
+  {
+    return save_str_value_in_field(field, &str_value);
+  }
   table_map used_tables() const { return (table_map) 1L; }
   bool const_item() const { return 0; }
   bool is_null() { return null_value; }

sql/item_strfunc.h

@@ -434,6 +434,10 @@ class Item_func_user :public Item_func_sysconst
   }
   const char *func_name() const { return "user"; }
   const char *fully_qualified_func_name() const { return "user()"; }
+  int save_in_field(Field *field, bool no_conversions)
+  {
+    return save_str_value_in_field(field, &str_value);
+  }
 };