MDEV-15530: Variable replicate_rewrite_db cannot be found in "show global variables"

- Add `replicate_rewrite_db` status variable, that may accept comma
separated key-value pairs.
- Note that option `OPT_REPLICATE_REWRITE_DB` already existed in `mysqld.h`
  from this commit 23d8586dbf

Reviewer:Brandon Nesterenko <brandon.nesterenko@mariadb.com>

sql/rpl_filter.cc

@@ -48,7 +48,7 @@ Rpl_filter::~Rpl_filter()
     free_string_array(&wild_ignore_table);
   free_string_list(&do_db);
   free_string_list(&ignore_db);
-  free_list(&rewrite_db);
+  free_string_pair_list(&rewrite_db);
 }
 
 
@@ -470,14 +470,6 @@ Rpl_filter::set_wild_ignore_table(const char* table_spec)
 }
 
 
-void
-Rpl_filter::add_db_rewrite(const char* from_db, const char* to_db)
-{
-  i_string_pair *db_pair = new i_string_pair(from_db, to_db);
-  rewrite_db.push_back(db_pair);
-}
-
-
 int 
 Rpl_filter::add_table_rule(HASH* h, const char* table_spec)
 {
@@ -520,6 +512,70 @@ Rpl_filter::add_wild_table_rule(DYNAMIC_ARRAY* a, const char* table_spec)
 }
 
 
+int
+Rpl_filter::add_string_pair_list(const char* spec)
+{
+  /* See also OPT_REWRITE_DB handling in client/mysqlbinlog.cc */
+  char* from_db, *to_db;
+  const char *ptr, *val_ptr;
+  size_t len;
+
+  // Remove pre-space in key
+  while(*spec && my_isspace(system_charset_info, (unsigned char)*spec)) spec++;
+
+  if (!(ptr= strstr(spec, "->")))
+  {
+    // Bad syntax, missing ->
+    return 1;
+  }
+
+  // value
+  val_ptr= ptr + 2;
+
+  // Skip blanks at the end of spec
+  while(ptr > spec && my_isspace(system_charset_info, ptr[-1])) ptr--;
+
+  if (ptr == spec)
+  {
+    // Bad syntax: empty FROM db (key)
+    return 1;
+  }
+
+  // key
+  len= (size_t)(ptr - spec);
+  if (! (from_db= (char *) my_malloc(PSI_NOT_INSTRUMENTED, len + 1, MYF(0))))
+  {
+    return 1;
+  }
+  memcpy(from_db, spec, len);
+  from_db[len]='\0';
+
+  // Remove pre-space in val
+  while(*val_ptr && my_isspace(system_charset_info, (unsigned char)*val_ptr)) val_ptr++;
+  // Value ends with \0 or space
+  if (!strlen(val_ptr))
+  {
+    // Bad syntax: Empty value \n"
+    my_free(from_db);
+    return 1;
+  }
+
+  for (ptr= val_ptr; *ptr && !my_isspace(system_charset_info, *ptr); ptr++){}
+  // value
+  len= (size_t)(ptr - val_ptr);
+  if(! (to_db= (char *) my_malloc(PSI_NOT_INSTRUMENTED, len + 1, MYF(0))))
+  {
+    my_free(from_db);
+    return 1;
+  }
+  memcpy(to_db, val_ptr, len);
+  to_db[len]='\0';
+  i_string_pair *db_pair = new i_string_pair(from_db, to_db);
+  rewrite_db.push_back(db_pair);
+  return false;
+}
+
+
 int
 Rpl_filter::add_string_list(I_List<i_string> *list, const char* spec)
 {
@@ -541,6 +597,14 @@ Rpl_filter::add_string_list(I_List<i_string> *list, const char* spec)
 }
 
 
+int
+Rpl_filter::add_rewrite_db(const char* table_spec)
+{
+  DBUG_ENTER("Rpl_filter::add_rewrite_db");
+  DBUG_RETURN(add_string_pair_list(table_spec));
+}
+
+
 int
 Rpl_filter::add_do_db(const char* table_spec)
 {
@@ -557,6 +621,14 @@ Rpl_filter::add_ignore_db(const char* table_spec)
 }
 
 
+int
+Rpl_filter::set_rewrite_db(const char* db_spec)
+{
+  free_string_pair_list(&rewrite_db);
+  return parse_filter_rule(db_spec, &Rpl_filter::add_rewrite_db);
+}
+
+
 int
 Rpl_filter::set_do_db(const char* db_spec)
 {
@@ -665,6 +737,21 @@ Rpl_filter::free_string_list(I_List<i_string> *l)
 }
 
 
+void
+Rpl_filter::free_string_pair_list(I_List<i_string_pair> *l)
+{
+  i_string_pair *tmp;
+
+  while ((tmp= l->get()))
+  {
+    my_free((void *) tmp->key);
+    my_free((void *) tmp->val);
+    delete tmp;
+  }
+
+  l->empty();
+}
+
 /*
   Builds a String from a HASH of TABLE_RULE_ENT. Cannot be used for any other 
   hash, as it assumes that the hash entries are TABLE_RULE_ENT.
@@ -749,6 +836,34 @@ Rpl_filter::rewrite_db_is_empty()
 }
 
 
+I_List<i_string_pair>*
+Rpl_filter::get_rewrite_db()
+{
+  return &rewrite_db;
+}
+
+
+void
+Rpl_filter::db_rewrite_rule_ent_list_to_str(String* str, I_List<i_string_pair>* list)
+{
+  I_List_iterator<i_string_pair> it(*list);
+  i_string_pair* s;
+
+  str->length(0);
+
+  const char *delimiter= ",";
+  size_t delim_len= 0;
+  while ((s= it++))
+  {
+    str->append(delimiter, delim_len);
+    str->append(s->key, strlen(s->key));
+    str->append(STRING_WITH_LEN("->"));
+    str->append(s->val, strlen(s->val));
+    delim_len= 1;
+  }
+}
+
+
 const char*
 Rpl_filter::get_rewrite_db(const char* db, size_t *new_len)
 {
@@ -769,18 +884,6 @@ Rpl_filter::get_rewrite_db(const char* db, size_t *new_len)
 }
 
 
-void
-Rpl_filter::copy_rewrite_db(Rpl_filter *from)
-{
-  I_List_iterator<i_string_pair> it(from->rewrite_db);
-  i_string_pair* tmp;
-  DBUG_ASSERT(rewrite_db.is_empty());
-
-  /* TODO: Add memory checking here and in all add_xxxx functions ! */
-  while ((tmp=it++))
-    add_db_rewrite(tmp->key, tmp->val);
-}
-
 I_List<i_string>*
 Rpl_filter::get_do_db()
 {
@@ -815,6 +918,13 @@ Rpl_filter::db_rule_ent_list_to_str(String* str, I_List<i_string>* list)
 }
 
 
+void
+Rpl_filter::get_rewrite_db(String* str)
+{
+  db_rewrite_rule_ent_list_to_str(str, get_rewrite_db());
+}
+
+
 void
 Rpl_filter::get_do_db(String* str)
 {