MDEV-12070 - Introduce thd_query_safe() from MySQL 5.7

Merged relevant part of MySQL revision:
https://github.com/mysql/mysql-server/commit/565d20b44f24fcc855dc616164d87b03cfad10bc

sql/sql_class.cc

@@ -4509,26 +4509,47 @@ extern "C" const struct charset_info_st *thd_charset(MYSQL_THD thd)
   return(thd->charset());
 }
 
-/**
-  OBSOLETE : there's no way to ensure the string is null terminated.
-  Use thd_query_string instead()
-*/
-extern "C" char **thd_query(MYSQL_THD thd)
-{
-  return (&thd->query_string.string.str);
-}
 
 /**
   Get the current query string for the thread.
 
+  This function is not thread safe and can be used only by thd owner thread.
+
   @param The MySQL internal thread pointer
   @return query string and length. May be non-null-terminated.
 */
 extern "C" LEX_STRING * thd_query_string (MYSQL_THD thd)
 {
+  DBUG_ASSERT(thd == current_thd);
   return(&thd->query_string.string);
 }
 
+
+/**
+  Get the current query string for the thread.
+
+  @param thd     The MySQL internal thread pointer
+  @param buf     Buffer where the query string will be copied
+  @param buflen  Length of the buffer
+
+  @return Length of the query
+
+  @note This function is thread safe as the query string is
+        accessed under mutex protection and the string is copied
+        into the provided buffer. @see thd_query_string().
+*/
+
+extern "C" size_t thd_query_safe(MYSQL_THD thd, char *buf, size_t buflen)
+{
+  mysql_mutex_lock(&thd->LOCK_thd_data);
+  size_t len= MY_MIN(buflen - 1, thd->query_length());
+  memcpy(buf, thd->query(), len);
+  mysql_mutex_unlock(&thd->LOCK_thd_data);
+  buf[len]= '\0';
+  return len;
+}
+
+
 extern "C" int thd_slave_thread(const MYSQL_THD thd)
 {
   return(thd->slave_thread);

sql/sql_class.h

@@ -153,7 +153,7 @@ extern MYSQL_PLUGIN_IMPORT const char **errmesg;
 extern bool volatile shutdown_in_progress;
 
 extern "C" LEX_STRING * thd_query_string (MYSQL_THD thd);
-extern "C" char **thd_query(MYSQL_THD thd);
+extern "C" size_t thd_query_safe(MYSQL_THD thd, char *buf, size_t buflen);
 
 /**
   @class CSET_STRING
@@ -183,7 +183,6 @@ class CSET_STRING
   CHARSET_INFO *charset() const { return cs; }
 
   friend LEX_STRING * thd_query_string (MYSQL_THD thd);
-  friend char **thd_query(MYSQL_THD thd);
 };
 
 

storage/innobase/handler/ha_innodb.cc

@@ -2462,22 +2462,7 @@ innobase_get_stmt_safe(
 	char*	buf,
 	size_t	buflen)
 {
-	LEX_STRING* stmt;
-	size_t length=0;
-
-	ut_ad(buflen > 1);
-
-	stmt =  thd ? thd_query_string(thd) : NULL;
-
-	if (stmt && stmt->str) {
-		length = stmt->length >= buflen ? buflen - 1 : stmt->length;
-		memcpy(buf, stmt->str, length);
-		buf[length]='\0';
-	} else {
-		buf[0]='\0';
-	}
-
-	return (length);
+	return thd_query_safe(thd, buf, buflen);
 }
 
 /**********************************************************************//**

storage/innobase/handler/handler0alter.cc

@@ -4471,11 +4471,13 @@ prepare_inplace_alter_table_dict(
 		       || !innobase_fulltext_exist(altered_table))) {
 		/* InnoDB can perform an online operation (LOCK=NONE). */
 	} else {
+		size_t query_length;
 		/* This should have been blocked in
 		check_if_supported_inplace_alter(). */
 		ut_ad(0);
 		my_error(ER_NOT_SUPPORTED_YET, MYF(0),
-			 thd_query(ctx->prebuilt->trx->mysql_thd));
+			 innobase_get_stmt_unsafe(ctx->prebuilt->trx->mysql_thd,
+						  &query_length));
 		goto error_handled;
 	}