[php-src] Issue #9787: Mysqlnd: packet headers bigger than buffer (4096) miss DB errors and put driver in inconsistent state

Issue: https://github.com/php/php-src/issues/9787 Author: wiebeytec ### Description The following was observed when using MySQL to communicate with Vitess, a MySQL database sharding layer. It is much more verbose in its errors (it prints the query back), so the following is triggered. I realize it's with Vitess, but mysqlnd shouldn't rely on conciseness of errors to keep from failing. The situation: The mysqlnd driver reserves 4096 bytes for the header buffer and when it's too big, it gives an error only visible in debug tracing. See [here](https://github.com/php/php-src/blob/ec55d341bff6a05e8f9dc257262e9b03b43ef358/ext/mysqlnd/mysqlnd_wireprotocol.c#L302). You then get a PHP warning "Error reading result set's header". This is a warning, not an exception, even though PDO is set to exceptions. Because it didn't finish parsing the packet, **it now doesn't realize this query failed**. Vitess rejected a NULL in a NOT NULL column. All php did was print a warning about the header, and then *next* queries complain about active queries in unbuffered mode (which is required for Vitess). The following code triggers it *but only on Vitess*: ``` create table mychars(val text not null); ``` ``` <?php // Won't fail on stock MySQL, but will on Vitess function connect_to_database_base($host, $user, $password, $dbname) : PDO { $db = new PDO('mysql:host=' . $host . ';dbname=' . $dbname, $user, $password, array( PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION, PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8 COLLATE utf8_unicode_ci', PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => false )); return $db; } function connect_to_database() : PDO { return connect_to_database_base("172.31.4.54", "user_dev", "password", "dbname"); } $db = connect_to_database(); // Create a long query, with invalid data. $myquery = "INSERT INTO mychars(val) VALUES ('first'), ('bla "; for ($i = 0; $i < 800; $i++) { $myquery .= " bla "; } $myquery .= "'), (NULL)"; print("I'm going to perform this query:\n\n$myquery\n\n"); $db->exec($myquery); print("\nAs you can see, it generated an uncatchable 'warning'. PDO will now not see that it was an error.\n"); print("The only reason this error is detected, because we can't keep using the unbuffered connection. Doing a select:\n\n"); $db->query('SELECT * FROM mychars LIMIT 1'); print("End\n"); ?> ``` Resulted in this output: ``` I'm going to perform this query: INSERT INTO mychars(val) VALUES ('first'), ('bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla '), (NULL) Warning: PDO::exec(): Error reading result set's header in /root/reproduce_truncated_result_header_longtext.php on line 27 As you can see, it generated an uncatchable 'warning'. PDO will now not see that it was an error. The only reason this error is detected, because we can't keep using the unbuffered connection. Doing a select: Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 2014 Cannot execute queries while other unbuffered queries are active. Consider using PDOStatement::fetchAll(). Alternatively, if your code is only ever going to run against mysql, you may enable query buffering by setting the PDO::MYSQL_ATTR_USE_BUFFERED_QUERY attribute. in /root/reproduce_truncated_result_header_longtext.php:32 Stack trace: #0 /root/reproduce_truncated_result_header_longtext.php(32): PDO->query('SELECT * FROM m...') #1 {main} thrown in /root/reproduce_truncated_result_header_longtext.php on line 32 ``` But I expected this instead: ``` I'm going to perform this query: INSERT INTO mychars(val) VALUES ('first'), ('bla bla bla '), (NULL) Fatal error: Uncaught PDOException: SQLSTATE[23000]: Integrity constraint violation: 1048 target: vitess_production_clone.0.primary: vttablet: rpc error: code = InvalidArgument desc = Column 'val' cannot be null (errno 1048) (sqlstate 23000) (CallerID: userData1): Sql: "insert into mychars(val) values (:vtg1), (:vtg2), (null)", BindVars: {vtg1: "type:VARCHAR value:\"first\""vtg2: "type:VARCHAR value:\"bla bla bla \""} in /root/reproduce_truncated_result_header_longtext.php:27 Stack trace: #0 /root/reproduce_truncated_result_header_longtext.php(27): PDO->exec('INSERT INTO myc...') #1 {main} thrown in /root/reproduce_truncated_result_header_longtext.php on line 27 ``` * I expect that the fact that the query gave an error was properly registered (*it is not now*) * I also expect that the connection doesn't keep a cursor open and so doesn't fail on subsequent queries. Tested with 8.1.11 tarball, compiled with debugging. ### PHP Version PHP 8.1.11, compiled debug version ### Operating System Ubuntu 22.04